Dictionary of Ichthyology

Brian W. Coad and Don E. McAllister^†

Revised: 08 March 2009

D

D = 1) abbreviation for dorsal fin (rays).

D = 2) Devonian, a geological period within the Palaeozoic Era ca. 413-365 million years ago; called the Age of Fishes.

D1 = abbreviation for first dorsal fin (rays).

D2 = abbreviation for second dorsal fin (rays).

D3 = abbreviation for third dorsal fin (rays).

D30 = number of dorsal fin rays to the 31st vertebra, e.g. in Carapidae.

D200 = number of dorsal fin rays to the 201st vertebra, e.g. in Nemichthyidae.

d bone = coronomeckelian (a small bone on the postero-lateral part of Meckel's cartilage of the lower jaw. Often a point of insertion of the adductor mandibulae muscle. Also called sesamoid angular, supraangular, sesamoid articular, articular sesamoid, splenial or os meckeli).

D-rig = a fishing rig where the bait is tied to a D-shaped loop on the back of the hook shank.

D-zone = that part of a microincrement of an otolith that is dark in transmitted light or is a depressed region when acid-etched and seen with a scanning electron microscope. It has more organic matrix and less calcium carbonate than the L-zone, q.v. Also called discontinuous zone or matrix-rich zone.

dab = 1) a common name for various species of flatfishes (Order Pleuronectiformes). Origin unknown.

dab = 2) the drowned corpse of an outcast woman (riverside thieves' slang, England).

dabber = dap (2).

dabbling = working a lure or bait up and down in the same spot repeatedly. Usually carried out from behind cover such as a bush or tree.

dacker = the ripple in water caused by the rapid motion of fish under the surface (Scottish dialect).

dacriform = tear-drop shaped.

dactylogyrosis = infestation with trematodes (Dactylogyrus spp.) causing the fish to secrete more mucus, paling of gills, opening of the operculum, difficulty in respiration and gill dropsy.

daeng = gutted and split milkfish (Chanos chanos) or Indian mackerel (Rastrelliger spp.) brined and sundried (Philippines).

Dagon = the fish god of the Philistines, the upper half being a man and the lower half a fish. The fish half represented fertility. The name is from the word dag, meaning fish. The Babylonians had a myth of a being who emerged from the Erythraean Sea, being part fish and part man. Also found in Assyrian sculpture.

Dahlgren's neuron = one of a series of nerve cells which are neurosecretory and located in the caudal neurosecretory system. The cells may be neurosecretory giant-cells, two or three times as large as ordinary neurons, and may exceed 100 microns in diameter. They have a nucleus which is polymorphic. Very small fishes may have Dahlgren's cells which are very small and not histologically distinguishable.

dahn = a small, flagged buoy attached to the end of fixed gear to mark its position.

daily growth increment = daily increment.

daily increment = a D- and L-zone on an otolith formed in a day. Also called daily ring, daily growth increment.

daily limit = the number of fish that an angler can retain from a day's fishing.

daily limit 0 = for conservation purposes, fish caught by anglers must be returned alive to the water. Also called catch and release, closed to retention and non-retention.

daily ration = amount of food consumed in a day.

daily retardation of tides = the amount of time by which a tide grows later day by day; about 50 minutes.

daily ring = a growth increment of one day on an otolith or scale in young fish, formed as a result of a circadian rhythm. Not found in adults or under conditions of poor growth. Daily increment is a preferred term.

daliane = a structure of wood or netting directing fish into a trap. Made to intercept large schools of tuna or mullets in the Black Sea and dependent on a watchman to close the trap entrance or lift the net floor after the school enters.

dam = a barrier controlling the flow of water and backing up water. Forms a lacustrine habitat (the reservoir) for fish where one did not exist before. Initially fish production is very high when stocked but declines as nutrients from flooded terrestrial ecosystems are used up. Release of water from reservoirs may radically affect fish downstream by changes in temperature regimes, flushing of habitats, and changes in silt loads. Storage dams store water and diversion dams divert water.

dambo = a shallow depression, having water seasonally and usually found near a river (South-central Africa).

Dame Juliana Berners = reputed author of "A Treatyse of Fysshynge with an Angle" from "The Boke of St. Albans" in 1496, the first evidence of fishing as a sport and the first literary treatment.

damp = a low grade of dried and salted cod (Newfoundland).

damp fishes = a checklist used by English Heritage Inspectors when making a description of a building to be preserved:- B, building type; D, date; A, architect; M, materials; P, plan; F, facade; I, interiors; S, subsidiary features; H, history; E, extras; S, sources.

damper - dap (2).

dan leno = a part of a trawl, the short pole or spreader to which each wing end was attached (probably from a corruption of the French word guindineau).

dan leno arm = butterfly (an L-shaped steel plate shackled between the dan leno spindle and legs. Also called arm, banana, boomerang, dan leno bracket, dan leno spreader, devil's elbow, spreader bar).

dan leno board = a small otter board.

dan leno bobbin = a large and hollow steel ball on a trawl between the otter boards and the net; functions to prevent the trawl wings from becoming entangled with small objects.

dan leno bracket = butterfly (an L-shaped steel plate shackled between the dan leno spindle and legs. Also called arm, banana, boomerang, dan leno arm, dan leno spreader, devil's elbow, spreader bar).

dan leno hoop = a hoop-shaped dan leno made of bent wood with short rigging ropes wired to the outer circumference. Also called dan leno ring, geer, hoop, hoop bridle, round dan leno and yoke hoop.

dan leno ring = dan leno hoop.

dan leno spindle = a steel spindle through a dan leno bobbin. Also called axle or spindle.

dan leno spreader = butterfly (an L-shaped steel plate shackled between the dan leno spindle and legs. Also called arm, banana, boomerang, dan leno arm, dan leno bracket, devil's elbow, spreader bar).

dan leno stick = a ballasted wood pole with short rigging ropes attached, functioning like the dan leno bobbin.

dan leno triangle = a triangular piece of steel, functioning like a bobbin.

dance = 1) fish dance (a dance of Great Lakes Indians involving flipping motions of the hands and feet).

dance = 2) fish dance (any of a variety of dances world-wide involving fish and fishing, meant to improve catches by propitiating gods or celebrating a way of life).

dance = 3) a general term for reproductive behaviour involving stylised and formalised movements by the male and female pair.

dandy = 1) a paternoster (a fishing rig where the hooklength branches from the mainline. Various styles exist and may have rigid wire branches with several hooklengths. St. Peter is supposed to have used a paternoster ("our father") rig to catch fish, hence the name).

dandy = 2) the wire or rope used to bring the aft end of the trawl beam alongside when hauling.

dandy bridle = dandy (2).

dandy line = a fishing line, specifically for herring with bare white hooks, suspended by whalebone kept in place by a lead (Shetland Isles dialect).

dandy winch = the small winch positioned aft, used when bringing the trawl beam alongside. Also called dandy wink.

dandy wink = dandy winch.

Danish jar = a wide-mouth glass container with a snap-on polyethylene lid. Also called Copenhagen jar.

Danish pond = an aquaculture pond made by excavation or by constructing dykes, usually 10 times longer than wide, with a bottom that may require sealing or lining to prevent water loss. Also called earthern pond.

Danish seine = a seine or cone-shaped otter trawl which is hauled over an area of about 2 square kilometres to a stationary vessel from an anchor buoy, the very long towing ropes disturbing clouds of mud which help herd the fish into the net. Also called anchor seine, Danish seine trawl, Danish trawl.

Danish seine trawl = Danish seine.

Danish trawler = a vessel 60-65 feet long, over 10 gross tons, with a crew of two or three. The wheelhouse, engine and accommodations are forward and the fish hold is aft. The hauling ropes of the Danish seine are coiled into the well decks.

Danish trawl = Danish seine.

danleno = dan leno.

danleno spreader = dan leno.

dap = 1) to fish by letting a fly or baited hook touch the water surface, using a short piece of line on a long rod.

dap = 2) to fish for cod with a hand-line, weighted hook and bait near the surface of the water (Newfoundland).

Daphnia = water fleas are used as food for fish in aquaria.

dapping = touching a fly to the water surface immediately over where a fish lies, using a short piece of line on a long rod.

dark meat = 1) a commercial measure of fish flesh colour, e.g. canned tuna is dark meat or dark tuna when it does not meet the colour requirements of light meat, q.v.

dark meat = 2) muscle from just under the skin on each side of a fish that is darker and richer in fat than other flesh. Also called blood meat, brown muscle, dark muscle, red muscle.

dark muscle = dark meat (2).

darne = a cut of steak of round fish cut on the bone.

dart (noun) = 1) an Inuit harpoon used to kill salmon and char (and seals).

dart (verb) = 2) to kill fish and seals with a spear or harpoon.

darter = 1) a member of the family Percidae, small colourful fishes found only in North America.

darter = 2) a type of plug used in angling. It floats when at rest but on retrieval submerges and wobbles and weaves. Used especially for bass (Centrarchidae).

darting = the spearing of fish.

darting speed = burst speed (the maximum speed a fish can maintain for a short period (5-10 seconds). Used in seizing prey or escaping a predator).

Darwen salmon = dogfish (Squalus acanthias) dried in air with the skin removed to disguise it; sold as salmon in the Highlands of Scotland and known by this name in Lancashire down to the 1950s.

Darwin fish = a car bumper sticker or symbol comprising the outline of a fish with short legs and the word Darwin in the centre of the fish body. Shows that the person believes in evolution. A parody of the Christian fish symbol.

Darwin's Nightmare = a 2005 movie about the exotic Nile perch in Lake Victoria, flash-frozen for export to wealthy countries, and the devastating effect this introduced fish has had on the people of the region and the native cichlid species flock.

dash = an elongate or streak-like melanophore in larval fishes.

dasher = a device used to scare fish into nets, either by making noise or by its reflective surface flashing light (Newfoundland). See also douser, thrasher and trouncer.

data (singular datum) = facts that result from measurements or observations.

data base = a consistent set of data that can used for analysis, e.g. counts and measurements of fish structures used in defining and diagnosing species. Also refers to the computer software in which the data is stored.

data deficient = in the IUCN Criteria for threatened species, a taxon is Data Deficient when there is inadequate information to make a direct, or indirect, assessment of its risk of extinction based on its distribution and/or population status. Abbreviated as DD. A taxon in this category may be well studied, and its biology well known, but appropriate data on abundance and/or distribution is lacking. Data Deficient is therefore not a category of threat or Lower Risk. Listing of taxa in this category indicates that more information is required and acknowledges the possibility that future research will show that threatened classification is appropriate. It is important to make positive use of whatever data are available. In many cases great care should be exercised in choosing between DD and threatened status. If the range of a taxon is suspected to be relatively circumscribed, if a considerable period of time has elapsed since the last record of the taxon, threatened status may well be justified.

data set = data and accompanying documentation which relate to a specific theme, e.g. catches by vessel type for a certain year, counts and measurements used in describing a fish species.

database = data base.

dataless management = management of a fishery based on the available information, without delay due to lack of technical data.

date fish = not a fish but a bivalve, Pholas.

date of collection = the calendar date on which a specimen was collected in the field. Accession dates and catalogue dates may be months or years later.

date of publication = the first day, reckoned according to the Gregorian calendar, on which copies of the publication became available by purchase or free distribution (not necessarily the date printed on the work itself). This applies to a work (and to a contained name and nomenclatural act). If the actual date is not known, the date to be adopted is regulated by the provisions of the International Code of Zoological Nomenclature.

datum = 1) the singular of data.

datum = 2) any position or element in relation to which others are measured, e.g. water levels in rivers, tides.

daughterless = a gene that can be inserted into fish eggs producing 80% males. This may be used as a means of controlling invasive fish species as long as the gene cannot move between species.

day = fish day (a day on which fish is eaten according to religious requirements; a fast day).

day boat = a boat making a one day fishing trip.

day length = the duration of the light period in a given 24 hours. Day length or daylength may be manipulated for aquaculture purposes such as early smoltification and breeding.

day ticket = a fishery where anglers purchase a ticket for the day's fishing on arrival.

day-class = the cohort of fish spawned or hatched on a given day or date. May be date of spawning or date of hatching.

day-degree = a unit taking temperature and time in days into consideration to indicate degree of development. Calculated by adding the average daily temperature for each day, e.g. if the average daily temperatures that a 3-day-old trout egg has been subjected to are 11, 12 and 13 degrees centigrade, the eggs are at the 36 day degree stage. This is abbreviated 36 D. Abbreviation Dº.

de- (prefix) = down, away, from.

de-listing = removal of a species from a list of threatened and endangered species.

deaccession = 1) a specimen removed permanently from a museum collection.

deaccession = 2) the process of removing a specimen from a museum collection. Material may be deaccessioned if it is found to belong to another institution, is to be donated to another institution, has deteriorated beyond any use, is required for destructive analysis, etc.

dead as a herring = 1) quite dead.

dead as a herring = 2) dead as a shotten herring.

dead as a shotten herring = an expression based on the perception that a spawned-out herring dies quickly (obsolete).

dead cat on a line = an indication that something is amiss or fishy. Derived from trot-fishing for catfish; if there is a dead catfish on the line then the line has not been checked by the fisherman for some time, indicating that something is awry.

dead drift = the way artificial flies drift with the current so as to appear natural; this requires that no part of the line and rig cause unnatural drag, frightening away the fish.

dead fish polo = a game involving canoes and a "fish" (really a sponge). The aim is to fling the "fish" into an opponents canoe using a paddle; if the "fish" lands in your canoe, you are out of the game.

dead lake = an ageing lake, overgrown with aquatic vegetation.

dead salmon = a proprietary paint colour, the name coming from a painting bill for the Library at Kedleston in 1805. Similar to smoked trout, a pinkish grey.

dead sock = a sock-shaped, lower extension of the net in a fish cage used in aquaculture.

dead spot = an area of a water body where circulation is minimal and anaerobic conditions develop, e.g. in an aquaculture pond.

dead water = 1) unmoving water in a water body.

dead water = 2) the eddy water behind the stern of a boat.

dead zone = a very large dead spot in the ocean, e.g. the seasonally-depleted oxygen levels (< 2mg/l) in the Gulf of Mexico covering 18,000 sq km (increasing each year - expected to be 22,126 sq km in 2007). Fish can swim away from such areas if onset is gradual but many invertebrates die. Caused by algal blooms dying and sinking to the bottom where the decay process depletes oxygen. The algal bloom can be caused by runoff fertilisers.

deadbait = dead fish used as bait in angling.

deadfall = dead trees fallen into the water providing cover for fishes.

deadfish grind = a move in inline skating by which the skater’s leading foot slides sideways while the trailing foot rolls on only the front wheel.

deadhead = a submerged log close to the surface but not lodged in the river bottom. Dangerous to motorised traffic. Sometimes used as a mooring buoy. See also planter (3).

dealer = 1) a middleman between the fishermen of a locality and fish merchants in a central community (Newfoundland).

dealer = 2) a fisherman operating under a credit or truck system (q.v.) (Newfoundland).

death assemblage = thanatocoenosis (an assemblage of organisms or their parts brought together after their deaths, e.g. fish bones by flowing water).

death rate = ratio of death to population, usually given as a percentage.

deboned fish = the flesh of a fish separated from skin and bones by mechanical means (see bone separator). Also called minced fish, mechanically recovered fish, recovered fish flesh, boneless fish and boneless fish meat.

debris catcher = trash collector (a wire fence across a stream used to retain debris and create a dam and a plunge pool; makes habitat for fish and collects gravel for spawning habitat. Also called trash catcher or grizzly).

debut line = the name of the first line thrown out of a boat to a man on the bank, as the boat is pulled across a river, casting out a net all the way. A Severn River, England salmon-fishing term. See also muntle.

decalcification = the absorption of calcium from bone, making the skeleton fragile, e.g. unbuffered formalin can become acidic and decalcify bone.

dechlorinating compound = a substance used to remove chlorine and neutralize chloramines from tap water for use in an aquarium. Charcoal does not remove chloramine.

deciduous = loosely fixed, easily detached, e.g. scales of Clupea.

decision analysis = a method that evaluates the expected outcomes, e.g. average catch, constancy of catch, probability of rebuilding to a given biomass target, etc., of alternative management controls used when there is uncertainty. A decision analysis can also address management consequences under different plausible assumptions about the status of the stock.

decision rule = control rule (a protocol for specifying harvest rates in relation to stock status and limit and target reference points. A harvest strategy expected to result in a long-term average catch approximating the maximum sustainable yield. Also called harvest control laws).

deck glass = a heavy sheet of glass in the bottom of a boat for viewing or spotting fish.

deck weight = deck-load.

deck-load = a pile of fish on the deck of a vessel.

deckhand = the all-purpose worker aboard a ship, usually paid a share of the profits on a fishing vessel.

Declaration = a minor and provisional amendment to the International Code of Zoological Nomenclature for immediate incorporation, published in the Bulletin of Zoological Nomenclature, to remain in force until ratified or rejected by future International Zoological Congresses.

decline = a reduction in the number of individuals, or a decrease of the area of distribution, the causes of which are either not known or not adequately controlled. Does not include natural fluctuations nor a planned fishery.

declivous = sloping downwards, declining.

decommissioning = removing a vessel from service and from the fishing register in the United Kingdom.

decompression sickness = gas bubble disease (supersaturated gases (>125%) in water entering the the body fluids of fish causing bubbles, an embolism). Also called bends or Caisson's disease.

decoy = an imitation of a fish used to attract fish close enough to be speared. Used in ice fishing in North America.

decumbent = bent downwards.

decurved = curved downward, usually in reference to the lateral line, e.g. in such cyprinids as Richardsonius, Notemigonus, Hemiculter, Aspius.

decussating = x-shaped, intersecting.

dee = deese.

Dee's disease = bacterial kidney disease (a bacterial infection with Renibacterium salmoninus or Corynebacterium sp. affecting salmonids, usually when temperatures are falling. The disease may be chronic or acute and has no treatment. Causes swelling of internal organs (oedematous, grey and corrugated kidneys with off-white lesions) and haemorrhages. Lesions may occur also in the liver and spleen and muscle contractions occur. External symptoms may be absent or include exophthalmy, skin darkening, abdominal swelling, and skin ruptures and vesicles. Also called Corynebacterial disease and kidney disease).

deem = used in taxonomy to indicate something that is not strictly true, e.g. a publication is deemed to be published by the author rather than by the actual publisher.

deep = 1) areas of deeper water between the shallower banks where fish are found and fished. Also called deeps.

deep =2) the number of meshes in one direction of a net.

deep cell = a cell in the blastodisc or blastoderm that is completely covered by other cells.

deep cell layer = a layer of deep cells of fairly uniform thickness that forms during early epiboly on conversion of the blastodisc to the blastoderm. This layer gives rise to the epiblast and hypoblast during gastrulation.

deep fore reef = the deepest seaward part of a coral reef; a vertical cliff beginning at a depth of about 60 m.

deep longline = a horizontal line with hooks lying on the sea floor.

deep sand bed = a filtration method in marine aquaria consisting of layers of sand up to 6 inches deep where anaerobic bacteria can grow and convert unwanted nitrates to nitrogen gas. Associated invertebrates burrow in the sand and facilitate a deeper penetration of the water.

deep scattering layer = a layer in mid-depths of the sea detected by echo sounders, which rises at night and sinks during the day. Composed of organisms, many of which have a gas filled chamber, such as certain jellyfish and fishes. Also called false bottom. Abbreviated as DSL.

deep sea (adjective deepsea) = the deeper parts of the ocean.

deep shelf and terrace = an insular horizontal habitat in the sea found at about 40 to 500 m. Interrupts a steeper slope and may occur in a series extending seaward from the shelf of an island or bank.

deep slope = an insular vertical habitat in the sea from about 40 to 500 m.

deep trap net = a pound net held in place under water by anchors and buoys.

deep water (adjective deepwater) = 1) permanent fresh water 2 metres below low water or the edge of emergent macrophytes, whichever is deeper.

deep water (adjective deepwater) = 2) ocean water where waves are not affected by bottom conditions; water deeper than one half a surface wave length.

deep-abyssal = waters of the sea below a depth of about 2,000 metres.

deep-drop = bottom fishing in deep water, sometimes in excess of 300 m, using a very large weight and circle hooks.

deep-sea = portion of the oceans below 200 metres or for deep-sea fish below 1000 m.

deep-sea trawl = the equipment used by a deep-sea trawler.

deep-sea trawler = a large long-distance trawler, not a vessel that fishes the deep-sea.

deep-skinned = fish prepared with the skin and the underlying fat layer removed. This gives a milder flavour and improves shelf life.

deepin worker = a net weaver.

deeping = 1) a section of a drift net twenty meshes deep, to which other sections are attached to the requisite depth.

deeping = 2) a strengthening band along the sole of a trawl, a score of meshes deep.

deeping = 3) the bag of a salmon net.

deeps = 1) the deepest parts of the oceans, where the bottom is below 3000 fathoms (5487 m).

deeps = 2) deep (1).

deepsea = adjective for referring to the deeper parts of the ocean.

deepsea trawl = the equipment used by a deep-sea trawler.

deepsea trawler = deep-sea trawler.

deepwater = 1) adjective for referring to deep water.

deepwater = 2) often used for any water of considerable, unpsecified depth.

deepwater species = in the sea, fish found at depths below 400 metres (bathypelagic, mesopelagic and benthopelagic fishes).

deese = a place where herrings are dried, the fish being hung on sticks (Sussex dialect) (deese may be the plural of dee). Also called herring hang.

deficiency disease = deficiency syndrome.

deficiency syndrome = improper feeding leading to abnormalities in behaviour, internal anatomy and function, growth and development.

definition = a statement of the characters that distinguish a taxon.

definitive host = the fish in which a parasite passes it adult or reproductive phase. Also called final or primary host.

deflector screen = a wire mesh screen installed where water is diverted from a stream or river to keep fish from entering the diversion channel or pipe. Also called diversion screen.

degenerate = said of a character or structure that has evolved to a less developed state from its ancestral state.

deglutition = the act or power of swallowing.

degree = 1) 1/360 of a circle or 60 minutes. The symbol here and below is °.

degree = 2) 60 nautical miles, 69.05 statute miles or 111.12 km.

degree = 3) a temperature unit (Celsius or Fahrenheit). Strictly 10°C is an actual temperature while 10C° is a range (from say 23 to 33°C).

degree = 4) water hardness, see degrees of water hardness.

degree day = see day-degree.

degree of digestion = digestibility.

degrees of water hardness = dGH (water hardness expressed in degrees of hardness. 0-4 is very soft, 5-8 soft, up to 30 which is extremely hard water). Note that different countries use different measures: 1 English (Clark) degree is 14.3 p.p.m. calcium carbonate, 1 American degree is 17.1 p.p.m. calcium carbonate and 1 French degree (fh) is 10.0 p.p.m. calcium carbonate. However 1 German degree (dh) is 17.9 p.p.m. calcium oxide. Confusingly the German dh is used generally for degrees of hardness.

dehydrated fish = fish that have been dried under controlled conditions with or without machinery but not be exposure to the climate.

dehydration = a white or yellow abnormality on the surface of frozen fish which masks the colour of the flesh and penetrates below the surface. It is caused by the sublimation process and the abnormality can only be removed by trimming away the affected parts.

deioniser = a device for filtering aquarium water using ion exchange resins.

delagic trawl = a trawl that can be fished demersally or pelagically without the gear having to be changed.

delay difference model = a type of biomass dynamic model used in fisheries that includes biologically meaningful parameters and accounts for time delays due to growth and recruitment.

delayed release = a change in the migration pattern of farmed salmonids, e.g. by feeding smolts in sea net cages before release to enhance the return rate.

delicatessen fish = fish prepared with salt, vinegar an spices, or smoked or salted and ready to eat but with a limited shelf-life.

délice = a neatly folded fish fillet.

delimitation = a statement of the character states which define the limits of a taxon; diagnosis.

delivery = casting an artificial fly to a fish or to an area of water suspected of holding fish.

delta = a fan-shaped or triangular alluvial deposit at a river mouth formed by the deposition of successive layers of sediment.

demand curve = relationship of price charged for a unit good such as fish per kg to the number of units a customer is willing to buy at that price.

demand feeder = a device allowing measured amounts of food to be delivered when triggered by fish in aquaculture. Also called pendulum feeder.

deme = an isolated population of a species tending not to interbreed (because of geographical barriers) with other populations; a local interbreeding group. Differs slightly in morphology or life history but not given taxonomic status.

demersal = sinking; bottom (e.g. eggs which sink to the bottom or are deposited on the bottom); dependent on the bottom. Said of fish that live near the bottom of the ocean, of a lake or of a river, but are capable of active swimming. Opposite of pelagic.

demersal fishery = a fishery concentrating on the capture of demersal species.

demersal pair trawling = pair trawling (bottom trawling by two vessels towing the same net. Very large nets can be towed in this manner by relatively small boats and the net is generally hauled alternately aboard the two vessels for processing of the catch. The net mouth is kept open by the outward pull of the two vessels).

demersal trawling = bottom trawling, e.g. otter trawl, beam trawl.

demersed = situated or growing under water, e.g. aquatic plants.

demi-sel = hareng saur or salted herring, partially desalted and cold smoked, whole ungutted or gibbed, also heads and gut removed. The curing time with salt is 2-3 weeks (France) It is called demi-sel when subject to prolonged desalting for more than 46 hours and lightly cold-smoked.

demi-vegetarian = a vegetarian who eats fish. See also pesco-vegetarian and pescatarian.

demography = the study of birth and death rates, age distributions and population sizes.

demophora = growth in demands on the freshwater supply and other finite environmental resources.

denatant = swimming, drifting or migrating with the current. Movement of eggs and larvae away from the spawning area. Opposite of contranatant, q.v.

denatured alcohol = ethanol rendered unfit for human consumption by addition of methanol (methyl alcohol or wood alcohol) or other substances. Used in some fish collections.

dendiculate = tooth bearing or having denticles. Also spelled denticulate.

dendric = a tree-like pattern; used to refer to branching of streams.

dendriform = a structure resembling a tree or shrub, branching extensively. See also dendritic and dendric.

dendritic = tree-like, branching. Used in reference to melanophores or to drainages.

dendritic drainage system = the commonest type of drainage system comprising a main river with tributaries that themselves have tributaries. Such a system usually occurs on a gentle slope. See also annular, deranged, parallel, rectangular and trellis drainage systems.

dendritic organ = a small arborescent organ found between the anus and the anal fin in certain Plotosidae (e.g. Plotosus, Cnidoglanis and Euristhmus). Organ with two main cell types, those with parallel groups of cytoplasmic tubules and many mitochondria, and clear cells with a network of cytoplasmic tubules. May have an osmoregulatory function. Also called arborescent organ.

dendrogram = a branching diagram that depicts the relationships between a group of items sharing a common set of variables. A phylogenetic dendrogram is called a cladogram, q.v.

denied name = nomen negatum (a denied name, an unavailable name which has incorrect original spellings as defined by the International Code of Zoological Nomenclature).

DeNiel fishway = a chute with lateral baffles that reduce the water's energy and leave a clear passage for fish to swim over the low barrier. There are no resting areas although pools may be provided for this purpose or to reduce flow velocity. See also pool-and-weir ladder, rock-ramp fishway and vertical slot fish passage.

denil fishway = DeNiel fishway.

denitrification filter = an aquarium filter that provides nitrate (NO₃) removal using anaerobic bacteria that separate nitrogen from oxygen.

dennage = dinnage.

dens acrodontis (plural dentes acrodontes) = acrodont (type of tooth ankylosed to the jaw along the midline of the jawbone, rather than to the inner edge, the condition in most fishes. Attachment is by connective collagenous tissue with impregnated calcium salts and, in maxillary and mandibular teeth, by a bony piece between the tooth and the bone).

dens incisoris (plural dentes incisores) = incisiform tooth (compressed and wedge-shaped tooth with a cutting edge resembling incisors of higher vertebrates, e.g. in Serrasalmus, the beak of Scaridae).

dens molariformis (plural dentes molariformes) = molariform teeth, shaped like a molar in mammals being round and flattened, used for crushing molluscs and crustaceans.

density = the number or weight of organisms per unit area or volume.

density dependence = the dependence of a factor influencing population dynamics (such as survival rate or reproductive success) on population density. The effect is usually in the direction that contributes to the regulative capacity of a stock.

dental formula = the number of teeth in a fish jaw, expressed as left and right (separated by a hyphen) and upper and lower (separated by a line). Symphysial teeth of different morphology may be interspersed between these counts. Counts are usually based on and expressed as ranges, seen over a sample of the species concerned, as individual counts differ. See also pharyngeal tooth count.

dentale = dentary.

dentary = the anterior, paired, dermal bone in the lower jaw. Usually the only tooth-bearing bone in the mandible, the two halves have a V-shape and meet at the jaw tip or mandibular symphysis. Posteriorly it has a coronoid process directed dorsally and a ventral process bearing the mandibular sensory canal on its outer face.

dentary elevation = the knob at the tip of the lower jaw at the junction of the dentaries which usually fits into an opposing indentation in the upper jaw.

dentate = having teeth or tooth-like points; serrate.

dentes acrodontes = plural of dens acrodontis.

dentes incisores = plural of dens incisoris.

dentes molariformes = plural of dens molariformis.

denticle = a small tooth-like body; also used for the placoid scale of Elasmobranchii. Also called dermal denticle.

denticular teeth = teeth on the snout and lower jaw of male Lophiiformes used to attach to the female.

denticulate = tooth bearing or having denticles. Also spelt dendiculate.

dentiform process= a tooth-like projection at the symphysis of the upper jaw in Balitoridae. It may fit into a notch in the lower jaw. Also called processus dentiformis.

dentigerous = tooth-bearing dermal bones, sometimes associated with endochondral bones. These bones are found on the mandibles, the tongue, the mouth cavity and the branchial apparatus. The teeth are formed independently of the bones but later in development join them by means of an intermediate tooth plate or by connective fibres.

dentigerous palatine = superficial bone bearing teeth covering the autopalatine.

dentine = a hard mesodermal material in teeth and some scales (cosmoid, ganoid and placoid scales) produced by odontoblasts. Like bone but without cells as the odontoblasts retreat leaving behind dentinal tubules (canaliculi) for protoplasmic processes.

dentition = tooth pattern, including arrangement and shape.

dento-spleniale = dentary.

depauperate = impoverished; said of ichthyofaunas or areas with little diversity in numbers or species.

dependent species = a species dependent on another for survival, e.g. a predator on a prey, commensalism.

depensation = mortality is depensatory when its rate (i.e. the proportion of population affected) increases as the size of the population decreases. Depensation may explain why marine fish populations like the Atlantic cod are slow to recover even when fishing is halted. Per capita mortality may increase because of changes in predator-prey interactions, mate availability may be reduced, fertilisation success may be lowered, operational sex ratios may change, and there may be a reduced intensity of social interactions during spawning. Compare compensatory mortality where the mortality rate decreases as the population size decreases. Depensation is also called the Allee effect.

depensatory = the adjective for depensation.

depleted = a very low abundance level of a stock caused by fishing as compared to historical levels.

depletion = for renewable resources, the part of the catch above the sustainable level of the resource stock.

depletion-based assessment technique = a prediction of how large the total (cumulative) removal would have to be in order to drive the relative abundance to zero. This predicted total removal is then an estimate of the initial stock size before removal begins.

deposit feeding = benthic feeding on plant and animal debris on or just below the bottom surface.

depredate = to capture prey (predate is not a verb unless you are dating before; the noun predation being often transformed into a verb meaning to capture prey).

depressed = flattened from top to bottom, e.g. Rajidae. Opposite to compressed.

depressed length = the length of a fin from its origin to the posteriormost point, measured when it is pressed against the body.

depressed fishery = a fishery with a declining population trend having occurred over a period of time appropriate to that fishery. The condition of a fishery that exhibits declining fish population abundance levels below those consistent with maximum sustainable yield.

depressed stock = a stock of fish whose production is below expected levels based on available habitat and natural variations in survival levels, but above the level where permanent damage to the stock is likely.

depressiform = depressed.

depression = any lower area, such as on the ocean floor.

depth = vertical distance through, height, e.g. body depth, caudal peduncle depth, head depth, etc., q.v.

depth contour = a map line connecting all points having the same water depth.

depth control = in angling, controlling the depth at which a lure or bait is fished.

depth finder = a sonar device used to determine depth and bottom structure and to locate fish.

deranged drainage system = a system without any obvious or coherent pattern as a result of much geological disturbance, as in areas cleared of soil cover by ice ages. The drainage patterns are still being determined and the glaciers left much water that accumulates in low points as lakes. See also annular, dendritic, parallel, rectangular and trellis drainage systems.

derby = a fishing competition with money and prizes for the best catches; used in North America.

derby style fishing = race-to-fish (a pattern of fishing characterized by an increasing number of highly efficient vessels fishing at an increasing pace, with season length becoming shorter and shorter; a management system where individual boats race to take as much of the total allowable catch before the fishery closes. Also called olympic fishing).

Derceto = the Syrian fertility goddess who fell into a lake at Bambyce near the Euphrates River in Syria. She was saved by a large fish and as a result ancient Syrians did not eat fish but worshiped their images as gods. Also known as Atargatis in Greek, whose temples contained fish ponds, the goddess punishing anyone who ate them by making them ill although her priests ate fish fish freely in a daily ritual.

derived = a character or character state not present in the ancestral stock; apomorphic. The term should not be applied to organisms or taxa since they are a mix of plesiomorphic and derived character states.

dermal = relating to the skin - the innermost of the two layers which arises from mesoderm.

dermal basihyal = basihyal (the cartilage supporting the tongue at the anterior end of the hyal series in Elasmobranchii. It is the anteriormost median endochondral bone of the basibranchial series, joining both branches of the hyoid series and forming the tongue skeleton in Teleostei. Dorsally is may have a dermal tooth plate called the glossohyal. The basihyal does not always ossify, e.g. in Salmonidae. Also called basihyobranchial).

dermal bone = any of the the superficial bones in Teleostomi derived from the dermis and overlying the deeper elements of the skull. Primitive fishes have more dermal bones than higher ones, e.g. the armour of Ostracodermi. Dermal bones are a form of membrane bones, i.e. they arose directly from connective tissue membranes without the cartilaginous precursors which precede endochondral bones. They may be divided into laterosensory canal bones that develop in relation to the sensory canals, bones derived from mesenchymous tissue and anamestic bones (q.v.). Also called achondral, membrane, investing and covering bones.

dermal crest = the adipose fin in Cobitidae and Balitoridae.

dermal denticle = a small, tooth-like, dermal scale in the skin of Elasmobranchii (except Torpedinidae) and the claspers of Holocephali. Also called more commonly placoid scale, although dermal denticle is more correct anatomically.

dermal ethmoid = supraethmoid (one of the paired dermal bones above the ethmoid, anterior to the frontals. Also called dermethmoid, mesethmoid and dermal mesethmoid rostral).

dermal flap = a small skin flap, e.g. in some Syngnathidae.

dermal fold = a flap distinct from the pectoral fin on the side of the head in Squatina.

dermal mesethmoid rostral = supraethmoid (one of the paired dermal bones above the ethmoid, anterior to the frontals. Also called dermethmoid, dermal ethmoid and mesethmoid).

dermal process = a conical process on the tip of the upper, and sometimes the lower, jaw, e.g. in some Gempylidae and Trichiuridae.

dermal supraoccipital = dermosupraoccipital.

dermarticular = the dermal bone of the lower jaw laterally covering and often fusing with the angular or retroarticular.

dermatocranium = the skeleton of the cranium derived from dermal bone that includes most of the superficial cranium bones. See also chondrocranium and splanchnocranium.

dermatone = a segment of skin innervated by one spinal nerve.

dermatotrich = dermatotrichium (1).

dermatotrichium = 1) dermotrichium.

dermatotrichium = 2) a secondary ray distal to a lepidotrichium also originating as a scale. Usually forked and lying on the edge of the fin, e.g. Doras and Synodontis in Siluriformes.

dermentoglossum = lingual plate (a dermal toothed bone covering and sometimes fusing with the basihyal, e.g. in Osteoglossidae. Also called glossohyal, entoglossum, os entoglossum, supralingual or basihyal dental plate).

dermestid colony = a colony of beetles (usually Dermestes) used for cleaning large fish skeletons of flesh. Also called bug colony.

dermethmoid = 1) supraethmoid (one of the paired dermal bones above the ethmoid, anterior to the frontals. Also called dermal ethmoid, mesethmoid and dermal mesethmoid rostral).

dermethmoid = 2) ethmoid (the deep, embryonic, perichondral, cartilaginous bone ossifying in and around the nasal septum. Later covered by the nasals, prevomer, adnasals (and rostrals) and located anterior to the orbit. It may not ossify in some Teleostei. Also called hypethmoid).

dermintermedial process = a small to large process on the floor or wall of the naris in some Sarcopterygii. May be covered in cosmine.

dermis = the innermost of the two layers of the skin, the outer being the epidermis. Contains the scales, blood vessels, nerves, chromatophores, connective tissue. Also called the corium. Of mesodermal origin.

dermocrania = plural of dermocranium.

dermocranium (plural dermocrania) = the superficial portion of the skull overlying the endocranium and consisting of a series of dermal bones over the outside of the skull.

dermohyal = the bone located between the opercular and preopercular in Palaeoniscidae.

dermopalatine = the paired dermal bone covering the undersurface of the autopalatines (q.v.) which are commonly called palatines, especially when the dermopalatine and autopalatine fuse.

dermopterotic = supratemporal-intertemporal (a dermal bone overlaying the pterotic (or autopterotic). Also called intertemporal and membranopterotic).

dermoskeleton = the bones of dermal origin, including scales, teeth, the dermocranium and the dermal pectoral girdle.

dermosphenotic = a superficial dermal bone behind the eye comprising the sixth infraorbital or suborbital; the dermal representative of the autosphenotic. Bears part of the suborbital and sometimes the conjunction of temporal, and supra- and suborbital sensory canals.

dermosupraoccipital = the superficial, paired dermal bone covering the supraoccipital with which it may fuse. In many Teleostei it is a hinge for the skull articulation with the circumorbital ring. Siluridae have a posterior toothed process that secures the nuchal disc. Also called parietooccipital, postparietal or dermal supraoccipital.

dermotrich = dermotrichium.

dermotrichia = plural of dermotrichium.

dermotrichium (plural dermotrichia) = the fin ray, of 4 types:- ceratotrich (in cartilaginous fishes), actinotrich (in cartilaginous and bony fishes), lepidotrichs (only in bony fishes) and camptotrichs (in Dipnoi and Crossopterygi). Spiny rays in Actinopterygii may be called acanthotrichs. Also called dermatotrich.

Derris = jewel vine, the plant from which the fish poison rotenone, q.v., is extracted. Also used as the word for the poison.

dervonic acid = docosahexaenoic acid.

descaling = 1) a condition in which a fish has lost a certain amount of scales.

descaling = 2) the removal of scales before cooking. Fins are usually removed first and scales are scraped away from tail to head using the back side of a knife; messy.

descargamento = lean meat from the area of the backbone of unspawned tuna, or any portions of flesh of spawned tuna, except belly flesh (Spain).

descr. = abbreviation of descriptione, meaning description.

description = a more or less complete statement of the observed characters of a taxon, without any special emphasis on those which distinguish it from other closely related taxa. The original description is the first, formal description of a new taxon.

descriptione = description, usually appearing as its abbreviation descr.

descriptotype = in taxonomy, that element or elements on which the original description was based.

deserticolous = living in desert regions; more applicable to terrestrial organisms than aquatic ones.

desiccated = completely dried; some specimens in museum collections may suffer this fate.

desiccated cod = small pickle cured cod, or trimmings obtained in boneless cod preparations, reduced to small fibres in a shredding machine and dried.

desiderata = wanted specimens or items.

designated unit = an infraspecific group which can be distinguished from the species and which has a different extinction probability.

designation = the act of an author or the International Commission on Zoological Nomenclature in fixing, by express statement, the type of a newly or previously established nominal taxon of the genus or the species group. The original designation is the designation of the name-bearing type of a nominal taxon when it is established. Subsequent designation is the designation of the name-bearing type of a nominal taxon published after the nominal taxon was established.

designation = the original designation is the designation of the type of a taxon when first established while the subsequent designation is the designation of the type of a taxon in a work published subsequent to the establishment of the taxon.

destructive sampling = removal or part or all of a museum specimen for some form of analysis (e.g. molecular work, toxicology) which gives results but destroys the sample.

det. = determiner.

det. = 1) abbreviation for determinavit, meaning (s)he identified or determined. Often used for identification notes in museum collections.

det. = 2) abbreviation for determiner.

detached breakwater = a breakwater (q.v.) not attached to the shore.

detention basin = an area that holds water for a limited period as a spillover from a larger basin to prevent flooding. All the water contained in the basin is released a short period of time. Not usually a fish habitat, cf. retention basin.

detention dam = a dam for temporary storage of water for later controlled release.

determinavit = meaning (s)he identified or determined. Often used for identification notes in museum collections as the abbreviation det.

determiner = the person who identifies a specimen. Abbreviated as det.

deterministic = a process that has no stochastic (random) components, e.g. the population model of some stock assessment methods assumes that population growth due to recruitment follows a deterministic formulation.

detrition = worn away by friction.

detritivore = feeder on detritus.

detritophagy = feeding on detritus.

detritus = 1) debris, disintegrated material or particulate material that enters into an aquatic system. If derived from decaying organic matter it is organic detritus.

detritus = 2) fragments formed by detrition, especially in fish gills.

detritus = 3) dead vegetal matter, faecal pellets and uneaten food forming a greyish gunk on the bottom of aquaria and in filter mechanisms. Rich in nutrients, it promotes algal growth and should be removed. Also called mulm.

detritus pool = the total accumulation of non-living organic matter in streams or rivers.

detrivore = detritivore.

deuterotype = a replacement type specimen.

devalid name = a name that is not valid because it was published before the starting date of the group concerned.

developed fishery = a fishery close to its maximum sustainable yield; a fishery operating at or near the level consistent with ecologically sustainable development in accordance with a management plan.

developing fishery = a fishery that is rapidly increasing often through increased fishing capacity.

development of shoreline = the ratio of shoreline length to the length of the circumference of a circle of the same area as the lake. Important in assessing fish habitat.

devil's elbow = butterfly (an L-shaped steel plate shackled between the dan leno spindle and legs. Also called arm, banana, boomerang, dan leno arm, dan leno bracket, dan leno spreader, spreader bar).

devil's thumb print = a dark blotch on the anterior flank above the pectoral fin of the haddock, Melanogrammus aeglefinus. The fish managed to escape the devil's grasp, which left the mark. Also called Saint Peter's mark.

Devon = two or more hooks embedded in a small artificial lure used in trolling.

Devonian = a geological period within the Palaeozoic Era ca. 413-365 million years ago; called the Age of Fishes. Abbreviated as D.

Devon spinner = Devon.

dextral = right-handed, e.g. referring to flatfishes having the right-hand side uppermost.

DFO = number of vertebrae anterior to the dorsal fin origin, e.g. in larval fishes.

dGH = water hardness expressed in degrees of hardness. 0-4 is very soft, 5-8 soft, up to 30 which is extremely hard water.

dh = DH.

dH = DH.

DH = hardness, expressed in degrees (Germany, from Deutsche harte). 1 DH = 17.86 p.p.m.

dhan = the marker buoy used as an anchor from which ropes and nets are set in, e.g. Scottish seining and fly dragging, q.v.

dhow = a traditional Arab sailing vessel, used for transporting fish in the Indian Ocean.

di- (prefix) = two, twice.

dia- (prefix) = across, through.

diacmic = having two maxima, e.g. during a growing season.

diacritic marks = diacritic marks, apostrophes or diaereses are not to be used in a taxonomic name and are to be deleted from such names originally published with them, e.g. the German umlaut sign is deleted from a vowel and should be replaced by an 'e' inserted after the vowel, but only for taxonomic names based on German words and published before 1985.

diadromous = those fishes which regularly migrate between fresh and salt water during a definite period of the life-cycle. Includes anadromous and catadromous fishes, e.g. Petromyzon, Alosa, Oncorhynchus, some Galaxias, Anguilla, Sicydium (Myers, 1949; McDowall, 1968).

diagnosis = a succinct and formal statement of the characters that distinguish a taxon.

diagnostic character = any character or character state that clearly differentiates one taxon from another.

diagonal file = fish teeth arranged in an in-between direction. Such teeth are at different developmental stages and derived from different tooth bud positions, cf. row and file.

diagonal scale row = the almost vertical row of scales slanting backwards and downwards across the sides of the body. Divided into scales above the lateral line starting at the front of the dorsal fin (from, but not including, the scale in the middorsal row, to but not including, the lateral line scales) and below the lateral line similarly ending at the front of the anal fin. The number of transverse rows themselves along the body may also be counted.

diamond cut = Aberdeen cut (a cut of fish from a frozen block, rhombus-shaped with the sides often squared off or cut with a tapered edge. Usually breaded and battered. Also called French cut).

diamond sinker = an elongate, diamond-shaped lead weight streamlined for trolling. Sometimes with a hook on one end and used for jigging.

diandric = adjective for diandry.

diandry = possessing two different types of males, a large, brightly-coloured and aggressive terminal phase (TP) and a smaller, drab and relatively non-aggressive initial phase (IP), e.g. in Thalassoma lunare (Labridae). The TP has priority access to food and spawning females. On the death or removal of a TP, the first-ranking IP becomes the next TP (after first checking the reef thoroughly to make sure the TP is gone). The two pathways of diandry are adult sex change as in monandry and also by direct male development from the juvenile phase with no adult sex change.

diapause = arrested development in the eggs of annual Cyprinodontidae. The temporary pool habitat dries up completely leaving the eggs to develop in the mud.

diaphanous = thin and translucent; semi-transparent.

diaphragm = a membrane between two chambers of the gas bladder which can be opened and closed by circular and radial muscles. Found in physoclist q.v. fishes but not Cyprinidae.

diaphragm pump = the most common type of aquarium air pump.

diapositive = a transparent photographic positive, a colour slide, a transparency.

diarthrosis = an articulation that allows free bone movement; cf. amphiarthrosis and synarthrosis.

diastema = a gap, e.g. in a tooth row such as in the upper jaw teeth into which a lower jaw canine fits.

diatom filter = diatomaceous earth used to remove very fine particles from the water in aquaria. They clog quickly and are only used occasionally as water polishers rather than continuously.

dibber = a small float with a bulbous tip, made of balsa or a peacock quill, and fished in canal shallows with casters as bait for roach (Rutilus rutilus).

dibble = skimming a wet fly leader or a bushy dry fly across the water surface to attract a bite.

diced fish = fish flesh cut into small cubes.

dichotomous key = an identification key using a series of alternative choices, each pair forming a couplet, that eventually lead to a species identity; the usual form of keys for fish identification.

dichotomy = bifurcation (a node in a tree connecting three branches. If one branch is directed or rooted, then one branch represents an ancestral lineage and the other two branches are descendent lineages).

dichromatic = having two colour forms.

dicht = to clean fish and prepare them for cooking (Scottish dialect, archaic English).

die-off = large numbers of dead fish through natural or unknown factors.

diel = daily, a 24-hour period.

diel vertical migration = a daily vertical migration.

diencephalon = a division of the brain, q.v. Major derivatives are the eye cups, the brain pretectal region, the thalamus, hypothalamus and epithalamus (including the habenula and epiphysis).

diet = 1) the food of a fish.

diet = 2) in aquaculture, a balanced mix of nutrients for normal health and growth usually provided on a schedule.

dietary efficiency = the efficiency at which a ration is converted to fish tissue.

dietary gill disease = a disease of fish caused by a deficiency in pantothenic acid.

dieter = 1) a person receiving winter board and accommodation against the promise of cash or service in the next fishing season (Newfoundland).

dieter = 2) a person helping in the preparatory work of the fishing season in exchange for board (Newfoundland).

differential diagnosis = diagnosis.

differentiation = becoming different in morphology, behaviour, physiology, etc., either within an organism's development or within a lineage of organisms.

diffuse spring = a spring fed by groundwater from many small cracks in the rocks and soil.

Digby chick = not a young bird but whole herring with guts heavily salted and cold smoked for 2-3 weeks until hard (red herring) prepared at Digby, Nova Scotia.

digestibility = 1) the degree to which a particular food can be digested and absorbed by a fish.

digestibility = 2) the nutrients absorbed by a fish, e.g. nutrient intake - nutrient remaining in faeces/nutrient intake, expressed as a percentage.

digestion coefficient = relationship of protein intake in a food to absorbed protein, expressed as a percent.

digestion efficiency = measured as the proportion of food that does not survive passage through the gut.

digestion rate = the time taken to digest food or the rate of passage through the gut.

digestive tract = alimentary canal (the passage through which food passes and is digested and absorbed; includes the mouth, oesophagus, stomach, intestine and anus. Also called alimentary tract and gut, although the latter might be more restrictive being areas of chemical processing and absorption only and not manipulation as with mouth and oesophagus and associated structures).

dight = dicht.

digit bias = a bias arising from the tendency of people to round off numbers to end in 0 or 5; important in angler surveys where catches are recorded from interviews. Also called rounding bias.

digitiform gland = rectal gland (an evagination of the terminal portion of the intestine of Elasmobranchii. Function formerly thought to be related to digestion or excretion, but now considered to secrete high concentrations of excess sodium chloride. Found also in the coelacanth Latimeria chalumnae).

dignathic = heterodont tooth morphology, differing in shape in the upper and lower jaws.

dike = 1) a protective wall around a fish pond.

dike = 2) a wall, levee or embankment to prevent flooding.

dilated = expanded.

dilator operculi = a muscle originating on the sphenotic posterior to the levator hyoideus and inserting on the dorsal medial surface of the operculum.

dim fish = dun fish.

dimethyl sulphide = a harmless chemical contaminant of Scomber scombrus, derived from eating pelagic snails. It gives an odour of petroleum products.

dimethylsulphoniopropionate = a chemical released by phytoplankton and benthic algae, associated with coral reefs, when eaten. Planktivorous reef fishes use this chemical as a foraging clue. Abbreviated as DMSP.

dimictic = a lake having two seasonal periods (fall and spring) of overturn with free circulation so surface and deep waters mix and the thermocline is disrupted.

dimorphic = having two forms.

dimpling = fish breaking the water surface, to feed on insects or attempting to escape predators, e.g. American shad, Alosa sapidissima.

dinghy = a small open boat.

dinglebar troll gear = one or more lines pulled through the water while the vessel is under way. The lines are set and retrieved using a troll gurdy with a weight from which one or more leaders with lures or baited hooks.

dink = 1) bass (Micropterus spp., Centrarchidae) too short to meet tournament standards; usually less than 14 inches (ca. 36 cm). Also called baby, throw back, nubbin, pop corn, and slick.

dink = 2) any very small fish.

dinmont = a an immature cod (Scottish dialect).

dinnage = brushwood, branches, boughs, bark, etc, placed as a mat on which dried fish is laid in a vessel's hold or spread on a flake (q.v.) (Newfoundland). Also spelled dennage, dynnage and dunnage.

dinogunellin = lipostichaerin (a toxic lipoprotein found in the Japanese Stichaeus grigorjewi (Stichaeidae). Probably analogous to "lipovitellin" in hen egg yolk. Called dinogunellin when the species was placed in the genus Dinogunellus.

dioecious = specie sin which the sexes are separate.

dip = 1) a bath treatment in which aquarium fish are immersed in a concentrated treatment solution for a short time to remove parasites or aid in disease cures.

dip = 2) immersion in a chemical solution or additive to improve shelf life and prevent moisture loss of fish prepared as food.

dip = 3) transferring fish from one holding area to another with a net.

dip = 4) the quantity of fish moved in a dip (3).

dip = 5) immersing nets and sails in a tanning liquid as a preservative (Newfoundland).

dip-net = 1) a bag-shaped net held open by a square, triangular or rounded frame on the end of a long pole. Used to scoop fish from the water, either on small scale in streams or ponds or commercially from large catches. May be quite large and pivoted on a scaffold or lifted by ropes or pivoted from the end of boat. Also called scoop or scoop net.

dip-net = 2) a net placed on the water bottom or suspended and lifted up when fish swim over it. More correctly lift net.

dip-net fishery = a traditional native fishery for salmonids where fish are captured using long-handled dip-nets, usually at waterfalls or other obstructions, which congregate the fish and make them more vulnerable to harvest.

diphagous = fish that eat in two different ways, e.g. Chauliodus sloanei.

diphycercal = an internally and externally symmetrical tail fin, e.g. in Dipnoi. May be secondarily acquired from the homocercal condition by loss of the real caudal fin and the gaining of a new one from dorsal and anal elements, e.g. in Gadidae.

diphyllobothriasis = a parasitic, intestinal disease of humans caused by eating raw of lightly processed fish. The parasite is a tapeworm (Diphyllobothrium) and man is the definitive host, fish the intermediate host. Also called Jewish housewife's disease or Scandinavian housewife's disease.

diplo- (prefix) = double, twofold.

diplodont = an early form of shark tooth, found in xenacanths for example, characteristically having two prongs or cusps. See also cladodont, hybodont and symmorid.

diplospondylous = referring to the double vertebrae formed when the anterior and posterior elements (sclerotomes) have not fused, e.g. caudal vertebrae of Amia. Two types of centra are present, a precentrum lacking neural and haemal arches and a postcentrum having these arches.

diplospondyly = the condition of a diplospondylous vertebra.

diplostomiasis = infestation of the fish eye by metacercaria of the fluke Diplostomum sp., eventually resulting in blindness. Snails are the intermediate host and piscivorous birds the final host. See also eye fluke disease.

diplotype = genoholotype (the primary type of the type species of the genus, designated by the author in the original description of the genus).

dippen net = dip-net (1) (English dialect).

dipping tub = a wooden tub used for immersing cod after being headed, gutted and split in Newfoundland.

dipsey sinker = a teardrop lead weight used for bottom fishing. The shape stops it catching on rocks.

dipsy = the float of a fishing line (Pennsylvania). See also dobber.

dipterex = dylox.

direct length = measurements of body parts are taken as the shortest distance between two points, not around the curve of the body.

direct methods = fishery independent research surveys used to estimate abundance and collect other biological data. Aims to avoid biases found in commercial catch data.

direct runoff = the runoff entering a channel promptly after precipitation.

directed fishery = a commercial effort aimed at catching a certain species or group of species. May also apply to a sport fishery.

Direction = a statement published by the International Commission on Zoological Nomenclature, completing or correcting an earlier decision given in an Opinion, a term now abandoned and replaced by Official Corrections.

dirty = said of transparent sea water in Newfoundland that has abundant large marine organisms which clog nets forming slub (q.v.), but lacks plankton which attract fish. See also clean.

dirty fishing = bycatch (fishes caught incidental to the target species; also called incidental catch or accidental catch. These fishes are usually of lesser value than the target species, and are often discarded. Some bycatch species are of commercial value and are retained for sale. The bycatch often consists of the juveniles of commercial species, and their loss has a deleterious impact on the overall yield obtained from a certain area. In a commercial fishery there are economic discards (fish thrown away for economic reasons, e.g. too small, damaged, not enough commercially value, etc.) and regulatory discards (fish thrown away because of the regulations as to size or species allowed to the fishery). Fish released alive under catch-and-release management programmes are not considered as bycatch. Also spelled by-catch).

dirty water = green or muddy water with highly reduced visibility; an angling term.

disappearance = the rate of decline in numbers of fish caught as fish become less numerous or less available. Often calculated from catch curves. Abbreviated as Z'.

disarticulated = 1) a fossil where the bones are separated and not together as in life.

disarticulated = 2) said of a fish skeleton prepared in a bug colony (q.v.) where the bones become separated after treatment or where bones are separated before exposure to the bugs to facilitate flesh removal.

disc = disk.

disc lamella = one of the flattened overlapping folds derived from fin rays on the head of remoras (Echeneidae) forming the sucker for attachment to other fishes and to whales.

disc teeth = teeth in the buccal cavity of Petromyzontidae.

discard = the part of a fish catch that is thrown overboard, but which may be of important ecological or commercial value. Also the act of throwing fish overboard. The discard typically consists of "non-target" species, damaged specimens or undersized specimens. The fish may be alive or dead, whole or in parts. Estimates of discards are made by observers and logbook records. Also called discarded catch. Discarding lower value fish to increase the value of a catch is called high grading.

discarded catch = the portion of a catch returned to the sea as a result of economic, legal or other considerations.

discard mortality = discard mortality rate multiplied by discarded catch.

discard mortality rate = the proportion of the discarded catch that dies as a result of catching or handling.

discard rate = the proportion of total catch which is discarded. Rates can be for individual species or groups of species.

discharge = flow of water in a river or drainage basin, measured in cubic feet per second (cfs) or cubic metres per second passing a certain point.

discharge area = the part of a catchment where groundwater appears as springs.

disciform = disc-shaped.

disclaimer = a statement in a work, by an author, editor or publisher, that the entire work or all, or specified, names and nomenclatural acts in it are to be excluded for purposes of zoological nomenclature.

disco maggot = a fluorescent-dyed maggot used as bait in angling in Europe.

discoidal = disc-shaped; flat and rounded.

discoidal organ = the modified pelvic fins formed into an adhesive disk.

discolouration = any of suite of abnormal colourings of commercial fish products other than liver stains (q.v.), e.g. blackening, browning, bruising, measured by area.

discontinuous zone = D-zone.

discontinuity = 1) an interruption; an obstacle to a stream continuum.

discontinuity = 2) check (a mark on a scale or other hard structure used for aging, caused by cessation of growth and absorption of deposited material due to spawning (hence a spawning check), injury, disease, parasites, or unseasonal lack of food).

discontinuity layer = thermocline (the zone of rapidly changing temperature between the warm upper layer (epilimnion) and the lower cold layer (hypolimnion). Characterized by a temperature change of 1C° or more per metre).

discrete fishery = a fishing region, or a fishery directed to a stock or species.

disgorger = a device of varying form, usually j-shaped with a slotted head to slide over the hook, used to extract hooks from a fish's mouth.

dish = a dish-shaped utensil used in hatcheries.

dished out = 1) a stream bank with an angle greater than 90 degrees. Also called laid back.

dished out = 2) any structure with a scooped out, dish-like form.

disjunct = distinctly separate; said of ranges that are discontinuous so that discrete, but potentially interbreeding, populations cannot interbreed.

disk (disc) = 1) the area surrounding the mouth in lampreys (Petromyzontiformes).

disk (disc) = 2) the roundish body of skate and rays (Rajiformes) excluding the tail and pelvic fins but including the pectoral fins that merge more seamlessly with the body.

disk (disc) = 3) an adhesive disk modified from the pelvic fins in, for example, clingfishes (Gobiesocidae), gobies (Gobiidae) and snailfishes (Liparidae).

disk drag = a system on fly reels that increases line resistance as a fish pulls it out. The resistance slows down and tires out the fish. The disk system is smoother than a click drag and line breakage is less likely.

disk length = the length from the snout tip to the posteriormost margin of the pectoral fin in Rajiformes.

disk width = the greatest distance between the lateral tips of the pectoral fins in Rajiformes.

dispersal = 1) an accidental migration, the outward spread of organisms from their point of origin.

dispersal = 2) the removal of copies of museum records and databases to a separate building from the originals as a safeguard against loss.

disphotic zone = dysphotic zone.

displacement = the behavior exhibited in an inappropriate situation occurring usually where there is conflict between incompatible instincts, e.g. aggression and flight, or when the external situation necessary for the completion of an activity does not appear (when a female stickleback does not follow a leading male).

disruptive colouration = an irregular colour pattern, often patches of light and dark, functioning as camouflage. The colour pattern disguises the fish's shape by breaking it up into visually distinct parts unlike a fish. Examples include eye stripes and ocelli. Even the stripes on a fish, individually distinctive, blend together and create the illusion of one large fish when schooling.

dissimilarity = a generic measure of the difference between two objects, measured on a scale of 0 to 1.

dissolved organic matter = minute organic matter.

dissolved oxygen = the amount of oxygen freely available in water and necessary for aquatic life and the oxidation of organic materials. For fish, ideal levels are about 7-9 mg/l and most fish cannot survive levels below 3 mg/l. Cold water contains more dissolved oxygen than warm and water too rich in bacteria and other aquatic organisms may use the oxygen up leaving none for fish. At 5°C brook trout use 50-60 mg of oxygen per hour but at 25°C they require 250-360 mg/hour as their metabolic rate increases. A value of 4-5 p.p.m. of dissolved oxygen is the minimum that will support a diverse fish community and values around 9 p.p.m. are preferred. Abbreviated as DO.

dissolved solids = very small pieces of organic and inorganic material contained in water. Excessive amounts make water less habitable for fish, unfit to drink or limit its use in industrial processes. Abbreviated as DS.

distad = in the direction away from the center of the body; remote from point of attachment, toward the outer edge. Opposite of proximad.

distal = at or near the outer edge or margin. Opposite of proximal.

distance = a measure of the difference between two objects, usually measured on a scale of 0 to infinity.

distance function = a measure of the "distance" between two populations in terms of the differences used in discriminatory analysis.

distant water fishery = a fishery carried out hundreds to thousands of kilometres from the home port of the fishing vessels, e.g. tuna fishery.

distavore = an eater of food from far away, opposite of locavore which is more politically and environmentally correct, e.g. a distavore in North America or Europe would eat Chilean sea bass from South Georgia.

distended scales = erected scales, a symptom of various fish diseases involving swellings such as dropsies.

distensible = capable of being extended or dilated.

distilled smoke = smoke with a high moisture content produced by slow burning wood, used to smoke fish.

distributary = 1) a diverging stream which does not return to the main stream but into another water body.

distributary = 2) a channel taking water from a canal for irrigation.

distrophic = dystrophic.

disturbance pattern = moving an artificial fly in such a way that it causes a disturbance in the water attractive to fish.

disturbance regime = the characteristics of natural disruptions such as a flood, in terms of timing, duration, intensity, etc.

ditch = a small artificial channel, a permanent or temporary habitat for fishes.

diter = dieter.

ditermous = having two nostril openings, anterior and posterior, the commonest condition in fishes. Monotermous is a single opening.

dither fish = a fish added to an aquarium with shy or nervous fish. A dither fish has a relaxed behaviour which encourages the other fish to come come out of hiding or to commence breeding.

diurnal = pertaining to daylight, active during the day; daily.

diurnal inequality = 1) the difference in height of the two high waters or of the two low waters of each day.

diurnal inequality = 2) the difference in velocity between the two daily flood or ebb currents of each day.

diurnal oscillation = the diurnal movement of plankton up and down in the water column, often mirrored by fish feeding on them.

diurnal tide = a tide with one high water and one low water in a tidal day (24.84 hours).

dive-caught = fish caught by hand, hand-held net or spear gun using a snorkel or scuba equipment. Highly selective and least damaging fishery method if carried out responsibly.

diver = in angling, a fly that dives below the water surface and floats back up on the retrieve. Used for bass and pike.

diver gill net = a gill net that drifts along the bottom, its weights being calculated to allow this, e.g. used in rivers for salmon.

divergence = the evolutionary process of branching lineages.

diverse = taxa or biota with many members, a wide range of morphology or of life histories.

diversion = the transfer of water from a stream, lake, aquifer, or other source of water by a canal, pipe, well, or other conduit to another watercourse or to the land, as in the case of an irrigation system. Often deleterious to fish populations.

diversion pond = a pond supplied by water by diversion of a stream.

diversion screen = a wire mesh screen installed where water is diverted from a stream or river to keep fish from entering the diversion channel or pipe. Also called deflector screen.

diversity = 1) a parameter describing, in combination, the species richness and evenness of a collection of species. Low diversity means few species or unequal abundance, high diversity many species or equal abundance. Diversity is often used as a synonym for species richness.

diversity = 2) the absolute number of species.

diversity = 3) variation in a trait or character, e.g. as in morphology.

diversity gradient = a regular change in diversity correlated with a geographic space or gradient of some environmental factor.

diversity index = a measure of the number of species in community and their relative abundances.

diverter = 1) fish diverter (an electrical device that prevents fish from entering sensitive areas, e.g. power dams).

diverter = 2) a ditch made to direct waste water from a given body of water.

diverticulum = an outpocketing or blind-ending tube from a cavity or blind sac.

diverticulum pharyngealis = epibranchial organ (a paired dorsal diverticulum at the posterior limit of the pharynx in certain microphagous fishes. Also called gill-helix, pharyngeal organ, or pharyngeal pocket. In all forms with these organs, except some characids, prominent gill rakers extend into the organ dividing its cavity into two parts, one confluent with the pharynx, and one with the opercular cavity. Small food particles, generally plankton, are retained by the rakers, consolidated by mucus and squeezed out into the oesophagus. Found in Heterotidae, Characidae, Chanoidei, Gonorhynchoidei, Clupeidae and Engraulidae).

division = a sea area designated for fishery management purposes, e.g. in the northwest Atlantic Ocean the sea is divided into seven subareas indicated by numbers and subareas into divisions indicated by letters, such that 0A and 0B are in Davis Strait while 3LNO covers the Grand Banks and nearby waters off Newfoundland.

djirim = heavily salted and dried flesh of sturgeons, an inferior form of balik (q.v.)(former Soviet Union).

DLS = abbreviation for double-layered spiral.

Dn = a photophore in front of and above the eye and the olfactory capsule of Myctophidae.

DO = abbreviation for dissolved oxygen (the amount of oxygen freely available in water and necessary for aquatic life and the oxidation of organic materials. For fish, ideal levels are about 7-9 mg/l and most fish cannot survive levels below 3 mg/l).

do-daudi = a simple drag net used on the Ganges River of India to catch small fishes. Operated by one person at each end having a bamboo pole attached to the net.

do-nothing rig = a rig comprised of a light-wire hook, a bead and a small brass sinker fished in clear water and often left alone. Bait is usually small worms.

doach = a salmon weir on the Scottish River Dee, also the name for the rocky stretch here. Also spelled doagh and dough.

doagh = doach.

doalie = a fisherman (Scottish dialect).

dobber = the float of a fishing line (New York). See also dipsy.

Dobriyal index = cube root of average gonad weight in grammes, used as a measure of reproductive capacity, determination of spawning season, sexual maturity and frequency of spawning (Dobriyal et al., 1999). Unlike the gonadosomatic index (q.v.), it does not involve body weight which is dependent on feeding intensity, food availability and environmental and physiological stress.

dobson = large brown aquatic larva of the dobsonfly; used as fishing bait.

dock = the waterway between two piers or a cut into the land for receiving ships.

docosahexaenoic acid = an omega-3-fatty acid found in fish which protects ageing rodent brains from the clumping seen in Alzheimer's disease. This chemical is formed in microalgae of the genus Schizochytrium and concentrated up the food chain to fish and other organisms. Chemical name is all-cis-docosa-4,7,10,13,16,19-hexaenoic acid. May account for the reduction in risk of dementia and stroke in humans as a diet of fish replaces DHA lost in ageing. Also called dervonic acid. Abbreviated as DHA.

doctor = a parasitic or other copepod which attaches itself to the wound of a fish (Newfoundland).

doctor fish = 1) any of a series of unrelated fish species that are supposedly helpful to other fishes, e.g. tench (Tinca tinca, Cyprinidae) slime is said to cure wounds; Garra rufa and Cyprinion macrostomum (Cyprinidae) in Turkish hot springs in the Kangal area clean dead skin fragments from humans with psoriasis; the circumpolar Gymnelus viridis or fish doctor may be a cleaner fish but the reason for its name is unknown.

doctor fish = 2) Acanthurus chirurgus, a member of the family Acanthuridae which is named for an extensible spine on each side of the caudal peduncle, resembling a scalpel in its sharpness. The spine is used in defence against predators and in dominance fights with members of its own species.

Doctor Fish Cafe = a chain of cafes and spas in South Korea where doctor fish are available for treatment of skin conditions in people. Spa resorts are now set up in various countries (China, Japan, Croatia, Singapore) with various names (not listed here). See also Fisho.

documentation = additional, supporting evidence on the identification, history, condition, scientific value, catch locality, etc. of a museum specimen or collection. May include paper records, photographs, old labels, field notes, other museum's catalogue data, etc.

doe = female salmon (in British Columbia).

dog hold = the hatchway in a jack-boat (q.v.) from which a man fishes (Newfoundland).

dog buoy = a buoy used to float fishing nets made from a dog skin. Dog skin lacked pores and was easily sealed with tar, e.g. used on the Moray Firth in Scotland.

dog ear = triangular pieces of netting fixed into the angle formed by the forward edge of a trawl having all bars along the hanging end points on the wings.

dog fishing = the Ainu of northern Japan taught their dogs to catch migrating salmon. The dogs are called Ainu dogs or Hokkaido inu.

dogfish = common name for various shark species, usually members of the Squaliformes which has about 100 species. Some species have commercial importance. The name may come from the fish being deemed unsuitable for human consumption but suitable for dogs or from the large schools of dogfish which fishermen called "packs".

dogfish head bones = chewed, these are folk cure for kidney troubles.

dogger = a two-masted fishing vessel, used by the Dutch.

doitsu = ornamental carp or koi (q.v.), with two lines of mirror scales.

dol net = a stationary net resembling a trawl using tidal flow to capture fish in India.

dole-fish = the share of fish allotted to each one of a company of fishermen in a catch.

doling = a fishing boat with two masts, each carrying a sprit-sail (Sussex dialect).

Dolly Varden = 1) the salmonid, Salvelinus malma, named for a female character in Charles Dickens' Barnaby Rudge who was colourfully dressed. A pink-spotted calico was called Dolly Varden during Dickens' visit to North America and the charr was likened to the material.

dolly varden = 2) a large earthenware crock used by fisherman in Newfoundland to drink tea.

dolphin = 1) one of a group of species of marine and riverine mammals.

dolphin = 2) confusingly, a fish, Coryphaena hippurus (Coryphaenidae).

dolphin-friendly tuna = tuna caught for food by methods that do not entangle or drown dolphins in the fishing nets.

domed-top float = a stick float used in angling for its greater visibility at distance. Also more buoyant and stable for fishing over depths.

domestic annual harvest = the domestic annual fishing capacity, modified by such factors as economics, which will determine estimates of what the fishing fleets will harvest.

domestic annual processing = the amount of fish that will be processed domestically, based on physical capacity but including such variables as demonstrated intent, markets, other fisheries, the effects of domestic harvesting, etc.

domestic fishery = 1) a fishery within national waters operated by nationals.

domestic fishery = 2) fishing for domestic consumption, subject to regulations.

domestic observer = privately employed individuals placed aboard fishing vessels to insure the legal catch of different commercial fish.

domesticated fish = a fish selected and adapted for aquaculture, for the aquarium or for pond keeping.

domhof knot = a knot used in angling to tie spade-end hooks to line. Various websites have animated steps showing how to tie this knot.

dominant = 1) the most numerous species in a community at a given time.

dominant = 2) used to describe a male fish which is the chief spawner and which endeavours to exclude other males from the spawning act.

dominant year class = a year class that predominates in the fishery, often continuing over several years.

domoic acid = an amino acid which is a neurotoxin. Found in algal blooms and can be eaten and concentrated by fish and transmitted to humans eating the fish.

donkey = a wooden barrel or cask for the export of dried and salted cod (Newfoundland).

donor = a person or organisation which has given a specimen or collection to a museum.

doondie = 1) a large lean cod (Orkney and Shetland dialect).

doondie = 2) a diseased cod (Orkney and Shetland dialect).

doondie = 3) a cod after spawning (Orkney and Shetland dialect).

door = 1) the entrance to a fish trap.

door = 2) a large, steel or alloy, door-shaped structure attached to the wire in front of a net (such as a trawl) to spread the net open by hydrodynamic action.

door legs = backstrop (a short wire or chain system between the otter board and bridle on an otter trawl. Also called backboard becket, backstrop, board bridle, board leg, board strop, door strop and sling).

door sling ring = backstrop link (a triangular steel link with rounded corners on the back of a trawl's otter board. The backstrop is attached here. Also called board link, shearboard link and VD link).

door strop = backstrop (a short wire or chain system between the otter board and bridle on an otter trawl. Also called backboard becket, backstrop, board bridle, board leg, board strop, door legs and sling).

doormat = a large flounder.

doorway = door (1).

doppel zentner = 100 kg. Abbreviated as dz.

dorie = a lead sinker on a mackerel line (Scottish dialect). See also dorro-bullet.

dorro (noun) = 1) a trailing cord with hooked lines attached used in catching cod, mackerel, ling, etc., jigged while the boat is rowed slowly along (Scottish dialect).

dorro (verb) = 2) to fish with a dorro (Scottish dialect).

dorro (verb) = 3) to fish in shallow water with a floating hand line (Scottish dialect).

dorro = 4) a wooden frame on which fishing lines and hooks are wound (Scottish dialect). See also grind.

dorro-bullet = a lead sinker at the end of a mackerel line, usually in the shape of a bell (Scottish dialect).

dorsad = above; toward the back; dorsal to.

dorsal = of or pertaining to the back, usually the upward side of a fish (except in flatfishes where the side uppermost in adults is a flank). Often used as an abbreviation for the dorsal fin. Opposite of ventral.

dorsal aorta = the principal, unpaired median artery of the trunk, extending into the tail as the caudal artery. Branches from this artery serve the viscera and the body muscles.

dorsal blade = a keel-like, medial structure anterior to the dorsal fin formed from the dorsal fin radials, e.g. in Sternoptychidae.

dorsal cerathyal = epihyal (the deep, endochondral bone at the upper end of the hyoid arch below the interhyal. It joins the hyomandibular and the symplectic through the interhyal, and articulates with the ceratohyal by a suture in some fishes, e.g. Gadidae. May bear a dentigerous plate. Also called posterohyal. It is called dorsal ceratohyal as it is considered to be the dorsal ossification of the ceratohyal. May or may not be homologous with the epal element of the branchial arches).

dorsal ciliated groove = hyperpharyngeal groove (the longitudinal ciliated groove on the upper wall of the pharynx which sweeps food particles to the oesophagus in Amphioxi and in the ammocoetes stage of Petromyzontiformes).

dorsal field = the uppermost area on a fish scale, between the anterior and posterior fields. Also called lateral field.

dorsal fin(s) = the unpaired fin(s) on the midline of the back. Also called the notopterygium. In Pleuronectiformes it is on the opposite side to the anus. In Centriscidae the hind end of the fish has been rotated under the fish so the dorsal fin is on the under surface. Abbreviated as D, D1, D2, or D3 respectively for the only, first, second or third dorsal fins (or their rays and spines). It functions to prevent rolling.

dorsal fin base length = the distance between the origin and the insertion of the dorsal fin; the length of that portion of the dorsal fin in contact with the body.

dorsal fin depressed length = the distance from the origin to the farthest posterior tip when the fin is flattened back down against the body.

dorsal fin height = the distance from the origin of the fin to the tip of the anterior lobe. Sometimes measured as the greatest vertical distance from the base.

dorsal fin ray count = enumeration of the dorsal fin rays. In fishes where the smaller rays in front gradually grade into larger rays, these smaller anterior rays are included in the count, e.g. Ictaluridae, Esocidae, Gadidae. Where the first small rays abruptly change to larger ones or where the first small rays are very variable or difficult to count these are not included; the first unbranched ray reaching nearly to the tip of the fin and the remainder of the rays are then counted - this is called the principal ray count. Where the last two rays are closely approximated at the base some authors consider them as a branched ray counting them as one (although they are not really a single branched ray). In fishes where the last two rays are not closely placed at the base, the rays are usually both counted. However some authors again count the last two rays as one. In some studies, only the branched rays of the dorsal fin are counted. It may readily be seen that if published counts are to be of use to others the method of counting should be stated. Dorsal fin spines, when present, are usually enumerated separately from soft or branched rays. The dorsal fin may be comprised of two connected parts, spiny and soft, counted separately, or there may be two dorsal fins, the first spiny.

dorsal rib = epipleural bone (rib)(one of a series of bones found in the horizontal septum (separating the upper and lower muscle masses of the body - epaxials and hypaxials). Epipleural ribs may be associated with the anterior pleural ribs, e.g. in Perca or the vertebra, e.g. in Gobiidae. Also called intermuscular bone).

dorsal stripe = the longitudinal arrangement of melanophores found along the dorsal side of the embryo underlying the median fin fold. The melanophores are in the midline of the anterior trunk and tail and are in two rows in the head and posterior trunk.

dorsicrania = plural of dorsicranium.

dorsicranium (plural dorsicrania) = a collective term for the endochondral and membrane bones of the dorsal skull region.

dorsohyal = dorsal hypohyal (see hyoid arch).

dorsolateral = between the back and the middle of the side, the upper area of the side.

dorsonasal photophore = light organ above the nasal aperture in front of the eye in Myctophidae. Abbreviated as Dn.

dorsum = the back or upper surface.

dory = a small, flat-bottomed, flared side and open but very stable rowboat often used in trolling and jigging. In Atlantic Canada, these 15 foot boats could be stacked on the deck of schooner and easily lowered over the side when the fishing grounds were reached. Two men fished from a dory, which could hold their gear, the catch and some food and water. A small sail could be raised. Each man operated 10 lines in the cod fishery, the lines being 52-55 fathoms long. The lines were connected together to form the trawl, 20 lines long or about one mile in length. Hooks were attached by gangings (branch lines), about 3.5 feet apart for a total of 1800 hooks on each trawl. The trawl was anchored at each end, marked by buoys. When the lines were hauled in by under-running (q.v.), one man removed the fish from the hooks and the other man re-baited them. Four sets would be made in a day. Dories were replaced by automated trawls in the 1960s but are still used inshore and as tenders.

dory banker = the dory used on the Grand Banks, Newfoundland.

dory banking = fishing with dories on the Grand Banks, Newfoundland.

dory boat = a larger form of dory used on the Grand Banks, Newpoundland, equipped with a 3-5 h.p. engine.

dory buff = yellow, the colour dories were often painted.

dory fishing = see dory.

dory hat = a waterproof hat with the brim the same size all around.

dory hook = part of the tackle used to lower a dory into the water and hoist it back onto the ship.

dory jig = a hook forming part of the hoisting tackle. See dory hook.

dory man = a fisherman who used dories.

dory master = the person in charge of the dory while it was away from the main vessel.

dory mate = fishermen who operated a dory together.

dory piggin = a bailing device, shaped like a dustpan, used to remove water from a dory.

dory pin = pegs on the side of a dory to keep the oars from sliding around.

dory schooner = the large vessel carrying dories for the Newfoundland cod fishery.

dory scoop = dory piggin.

dory skipper = the owner of a dory.

dosing pump = a pump which can supply a very slow drip used to add trace elements or make up water lost from evaporation in aquaria. The most common type is a peristaltic pump.

dosse = a pannier in which fish are carried on horseback (Sussex dialect).

dorsel = dosse.

dotting = in angling, the addition of small lead weights (shot) to the line so that only the tip of the float is visible above the water surface.

double bagging = splitting a catch in two when the catch is too heavy to deal with as a single unit.

double beam trawl = two beam trawls towed by one trawler.

double blood knot = a knot used in angling to tie together two pieces of line of similar or dissimilar diameters. Various websites have animated steps showing how to tie this knot.

double codend = two codends joined at the leading edge. Used on rough grounds to reduce the chance of total loss of a catch.

double cropping = having two populations in an aquaculture pond, cropped simultaneously or alternately, one of the crops not necessarily being fish.

double ebb = a tidal ebb current having two maxima of velocity separated by a smaller ebb velocity.

double emarginate = a caudal fin pointed at the end in the mid-line with the margins above and below that point indented.

double fillet = block fillet (a fillet comprising muscle mass from the side of the fish, usually joined at the back or belly. Also called angel fillet, butterfly fillet, etc.).

double flood = a tidal flood current having two maxima of velocity separated by a smaller flood velocity.

double half-hitch = a knot for tying up a boat. Bend the line around a post or through a ring and then pass its end over or under the standing part and up through the loop formed by the turn; doing this twice makes the double half-hitch. Various websites have animated steps showing how to tie this knot.

double haul = a fly cast where the angler quickly pulls and releases the line on both the back cast and the forward cast creating a greater line speed and casting farther or cutting through wind.

double hook = a hook with two points used in trolling.

double linnet = the overlap of netting formed when a cod trap is drawn to the surface (Newfoundland).

double loop clinch knot = a knot used in angling for tying on swivels when trolling. Various websites have animated steps showing how to tie this knot.

double mark = double zone (two rings on an otolith that are close together relative to the size of the calcified stricture and the distance between two annuli. Considered as one annulus).

double mesh = net mesh made with double twine where special strengthening is necessary.

double nail knot = a knot often used in saltwater fly-fishing to join leader sections of the same or slightly different diameter, being less bulky than a blood knot when using heavy leader material. A nail is used to help form the knot. See also nail knot and offset nail knot. Various websites have animated steps showing how to tie this knot.

double naping = cutting through both sides of the body wall of a fish.

double pump = the process employed by fish to move water over the gills for oxygen and waste exchange. The jaw and mouth are lowered and expanded, inhaling water into the oral pump or mouth cavity. Movement outward of the operculum expands the opercular pump or cavity and valves prevent a backflow of water. The two pumps are coordinated to provide a smooth flow of water over the gills.

double rigging = using outriggers to tow 2-4 trawls at once.

double ring = double zone (two rings on an otolith that are close together relative to the size of the calcified stricture and the distance between two annuli. Considered as one annulus).

double stick net = a form of scoop net with netting strung between two sticks and usually operated by one person. Used like a skimming net, q.v.

double surgeon's knot = a knot used to attach a tippet to a leader in fly fishing. A loop is made, a single overhand knot tied, and doubled. Various websites have animated steps showing how to tie this knot.

double taper = a fly line reduced in diameter on both ends; when one end wears out it can be taken off the reel and the other end used. Available in floating and sinking styles and good for short to moderate length casts and for roll casting.

double tide = a high water consisting of two maxima of nearly the same height separated by a relatively small depression, or a low water consisting of two minima separated by a relatively small elevation.

double truncate = a caudal fin pointed at the end in the mid-line with the margins above and below that point straight.

double turl knot = used on large flies or tippets as a single turl knot using synthetic lines tends to creep out because of their smooth finish. Various websites have animated steps showing how to tie this knot.

double zone = two rings on an otolith that are close together relative to the size of the calcified stricture and the distance between two annuli. Considered as one annulus. Also called double ring and double mark.

double-ender = a type of boat used in fishing, having a sharp stern as well as a pointed bow. Fishermen believed that following seas would not swamp such a boat, although this did not always work out in practice. Such boats were hauled up on the beach, e.g. in the Gaspé region on the south shore of the St. Lawrence River, and having a pointed stern made them easier to launch though surf. The Gaspé boat, Tancook whaler and Labrador boat are of this type.

double-frozen = fish frozen at sea then thawed for processing onshore and then re-frozen. Also called twice-frozen or refrozen.

double-layered spiral = a material made by rolling up a polyester pad and plastic wire mesh. It is used in both biological and mechanical filters in aquaria.

doubtful name = nomen dubium.

dough = doach.

dour = reluctance of fish to bite (Scottish dialect).

douse the killick = lowering an anchor with float attached to indicate occupancy of a particular fishing ground (Newfoundland). See also throw away one's grapnel.

douser = a device used to drive fish in a desired direction by thrashing the water (Newfoundland). See also dasher, thrasher and trouncer. A douser was a twelve or fourteen inch bolt of iron with four iron rings fastened through the bolt at three or four inch intervals. Dousers were bounced off the ocean floor to drive cod into the bag of a seine. Often, four or five douser were used at a time.

Dover cut = American cut (fish portions or fillets with tapering or beveled edges, rather than square-cut sides).

Dover sauce = Berwick sauce (the water in which a salmon has been boiled, served as a sauce).

Dover sole goujons = goujonettes de sole (sole filets baked or fried in bread crumbs and a light batter; the origin of fish sticks, q.v.).

dow = fish that are not fresh or that have been drying for a day or two (Scottish dialect).

dowe = dow.

down = 1) in the Newfoundland fishery, a location further out to sea, e.g. down the shore.

down = 2) in the Newfoundland fishery, describes the direction north so any place to the north of a particular location is down from it, e.g. down on the Labrador, down north.

downer = a steelhead salmon returning to the ocean. Also called snake.

downrigger = 1) a metal structure resembling an oversized fishing rod mounted on a boat and capable of being raised and lowered. Used to present lures in deep water on tight lines.

downrigger = 2) an electric or hand-powered winch used to lower a wire line with a cannonball (heavy weight) to a selected depth; a fishing line from a separate rod and reel is attached with a quick release clip. When a fish is hooked, the fishing line is released from the downrigger mainline so the fish can be played on tackle without a weight.

downrigger ball = a cannonball-shaped device with a fin used to keep a trolled bait far beneath the boat.

downriver = kelt (a spawned out or spent Salmo salar or other salmonid up until the time it enters salt water. A name used in British Columbia. Also called dropback).

downrunner = a fish returning to sea after spawning, e.g. American shad, Alosa sapidissima.

downshotting = dropshotting.

downstream = in the direction of water flow.

downstream angler harvest = that portion of a watershed's harvest that is taken downstream of the watershed.

downstream drift = allowing a fly to drift past the angler and rise to the surface downstream.

downwelling = a downward movement of surface water caused by onshore transport, converging currents, or dense water overlying less dense water. May carry fish to lower depths.

drab = a colour description of fish or body parts, meaning dull grey to yellowish brown, light olive brown or khaki, or faded and dull.

draft = 1) an old measure of dried, salt cod for sale, two quintals or 224 lbs or 101.6 kg. Also called draught.

draft = 2) a collective noun (a noun that denotes a collection of persons or things regarded as a unit) for eels.

draft barrow = 1) a flat, rectangular wooden frame with handles at each end for two men to carry dried cod (Newfoundland).

draft barrow = 2) a draft barrow frame used in weighing fish (Newfoundland).

draft netting = encircling fish with a net deployed from shore by a boat and then hauled into shore. Use to catch salmon in estuaries, especially in Ireland.

drag = 1) a device in the mechanism of fishing reels that puts pressure on the line as it is pulled off the reel, allowing a hooked fish to pull line without breaking it, and to restrain a running fish. Also called slipping clutch.

drag = 2) movement of an artificial fly at a rate different from the water current causing the line to form a v-shape at the surface and discouraging fish from biting.

drag = 3) to pull fishing gear through the water.

drag net = pull net (any net where fish are caught by horizontal dragging, e.g. seine, trawl, scoop net).

drag seine = beach seine (a net used to encircle fish in shallow water; usually operated by two people wading out from shore, the net has lead weights to keep the bottom on the sea floor and floats to keep the top of the net at or near the surface; there may be a bag extending back from the centre of the nets length to increase capture efficiency. The seine may be set from a boat but hauled in from the land. Also called shore seine, draw net, haul seine, yard seine and sweep net).

dragger = a trawler, a fishing boat that uses a trawl net or drag net to catch fish. Of varying sizes with a small crew of about three to eight people. The trawl is usually worked from the starboard side from winches geared to the main engine of the vessel.

dragger trawl = otter trawl (a towed net that strains demersal fish out of the water. Rectangular otter boards of wood or steel on the tow ropes plane through the water and help keep the mouth open and give the trawl its name; floats on the headrope and weights on the ground line also assist in this).

dragging = the operation of a trawl (a bag-shaped net towed behind a ship either along the sea floor or in midwater, having a buoyed head rope and a weighted foot rope to keep the net mouth open).

dragman = a fisherman who fished by dragging a net along the bottom of the water (archaic).

dragnet = drag net.

drail = 1) a heavy, boomerang-shaped lead weight with a ring at each end used as a keel when fishing in deep water.

drail = 2) a heavily-weighted hook and line used for dragging in deep water.

drailing = 1) trolling for mackerel with hook and line while under sail.

drailing = 2) drunk emailing.

drain = a ditch allowing improved drainage from fields, either artificially constructed or a modified natural watercourse. Often a habitat for fishes. Drains may also be a closed system of tiles buried in the ground.

drain box = monk (a weir structure used to regulate water depth in a pond with a screen to retain fish).

drain channel = a system for draining water; often a habitat for fishes either temp or permanently.

drain water = water drained off, especially by an artificial drainage system.

drain-bulk = a stage in the curing of cod in Newfoundland in which the split and salted fish are laid in piles to drain before being moved to the flake (q.v.) to dry.

drainable pond = a pond from which the water can be taken out, but not to an extenms that eventually enter the sea or the main chbasin. Includes any ponds or lakes.

drainage basin = the total surface land area drained by a stream or river; often used in the sense of the water bodies in the basin. Not a watershed which is strictly an elevated boundary area separating tributaries draining to different river systems.

drainage ditch = drain channel.

drainage lake = a lake fed primarily by streams and with outlets into streams. Such a lake has a shorter residence time than a seepage lake and is more subject to surface runoff problems.

drainage system = several types of drainage system for rivers are recognised, namely annular, dendritic, deranged, parallel, rectangular and trellis (all q.v.).

draining = draining surplus brine from a brined fish by leaving the fish hanging. Also called dripping.

draught = 1) draft.

draught = 2) a catch of fish in one drawing or pulling in of a net.

draught = 3) the act of drawing in fish.

draught = 4) a collective noun (a noun that denotes a collection of persons or things regarded as a unit) for fishes.

draught = 5) a collective noun (a noun that denotes a collection of persons or things regarded as a unit) for salmon.

draught bar = draught barrow.

draught barrow = a flat wooden barrow with handles for two people, used mainly for carrying dried fish in Newfoundland, slightly larger and stronger than a hand barrow for carrying a draught (two quintals) of dried fish and was used mainly on mercantile premises. Also called draught bar.

draught of fish = a haul of fish.

drave = a shoal of fish (archaic).

draven = decomposed, rotten or decayed fish (Scottish dialect). Also spelled dravin.

dravin = draven.

draw = 1) a tributary valley or gully, shallower than a gorge, and usually having water only after rain. Not usually a fish habitat.

draw = 2) to haul in a fishing net.

draw = 3) the selection by lot of a fishing location in the inshore fishery of Newfoundland.

draw = 4) to take fish out of pickle preparatory to washing and drying (Scottish dialect).

draw = 5) to catch fish with a handline.

draw net = beach seine, q.v., or a trawl, q.v.

drawdown = the release of water from the reservoir of a dam for power generation, flood control, irrigation or other water management activity. Also the vertical distance the water is lowered or the reduction in the pressure head. Often with deleterious consequences for fish both within the reservoir and downstream.

drawdown zone = the shore zone between full and lower levels in a reservoir.

drawing a red herring across the path = trying to divert attention from the main question by some side-issue. Derived from the use of a red herring drawn across a fox’s path, destroying the scent and leading the hounds astray.

drawing twine = the small mesh of the bunt in a cod trap where the fish collect when the trap is hauled to the surface (Newfoundland). See also drying twine, drawing up area and drying up area.

drawing up area = drawing twine.

drawn = eviscerated. Drawn fish may still need to be scaled.

dream fish = a Kyphosus species (Kyphosidae) of Norfolk Island, hallucinogenic if eaten because of dimethyltryptamine content.

dreams of fish = a dream seeing fish in clear-water stream shows favour from the rich and powerful; dead fish signifies loss of wealth and power through some disaster; eating fish denotes warm and lasting attachments, etc.

dredge barrow = barrow (a flat, rectangular wooden frame with handles at each corner, made for two men to carry cod. Also called fish barrow and drudge).

dredging = 1) the removal of material from the bottom of water bodies using a scooping machine. This disturbs the ecosystem and causes silting that can kill fish.

dredging = 2) retrieving a crankbait such that it digs into the bottom, stimulating strikes by fish.

dress = the process of dressing (1).

dress gang = the group on a fishing vessel responsible for cleaning, dressing and salting fish.

dress-out percentage = the percentage weight of the whole fish remaining after removal of the viscera, and sometimes also the head and tail as well.

dressed = 1) a fish with viscera, head and tail removed (some fish may have the tail on) but with skin and bone retained. Some dressed fish may have scales removed. A kitchen-ready fish. See also dressing.

dressed = 2) a lure or jig with feathers, fur, plastic or other additions meant to attract fish.

dressed green fish = split fish ready for washing and salting (North America).

dressed or dressing weight = the weight of a dressed fish, q.v. Fish are usually dressed at sea. Abbreviated as DWT.

dressing = the process of preparing fish and game for eating. Fifteenth century words no longer in use for fish include:-

bined = sole,

chined = salmon,

gobbetted = trout,

sauced = tench,

sided = haddock,

splated = pike,

splaved = bream,

trouchened = eel, and

tusied = barbel.

drew = 1) in knitting or making a fish net, a certain number of meshes formed in a row.

drew = 2) a quantity of dried and salted cod equal to the length of a storage pound.

dribble = a very small, barely continuous stream (Newfoundland).

driddle = dribble.

dried fish = fish preserved with a water content less than 25% (no bacterial growth) and 15% (no mould growth).

dried salted fish = fish preserved by salting and drying. Works best with non-fatty fish.

dried-up pond = a pond from which water can be totally removed, leaving the bottom available for cultivation, thus making the pond more fertile when refilled.

drier = fish flake (a rack on which fish are dried, often of spruce boughs on a framework of poles in North America).

drift = 1) to be carried along by water currents.

drift = 2) displacement by currents of invertebrates and plant material which is seized on by fish as food drift organisms.

drift = 3) a collective noun (a noun that denotes a collection of persons or things regarded as a unit) for fishes.

drift anchor = an anchor in the water column like a kite that slows the movement of an angler's boat through a fishing area.

drift bay = drift anchor.

drift boat = a river fishing boat with a flat bottom, rigid hull and upswept prow about 14-18 feet long. Also called a Mackenzie River dory.

drift castnet = a castnet in which half is lowered into the water from a boat, the other half resting on the gunwhale. The boat drifts with the current which keeps the net open. When the fisherman feels a fish touch the net through the vibration of a rope attached to his foot, he releases his hold on the net so it falls to the river bottom, trapping the fish.

drift current = a broad and shallow, slow-moving current in a lake or the ocean.

drift fish = drift food.

drift fishing = 1) using a series of gill nets which are allowed to drift in the open ocean.

drift fishing = 2) angling from a boat allowed to move with the current, wind or tide.

drift fishing = 3) casting a weighted bait upstream and allowing it to drift downstream. The weight and bait bounce along the bottom.

drift food = fish washed up on shore, e.g. capelin (Mallotus villosus) and cod (Gadus morhua) in Iceland where they drift-fish rights (q.v.) existed.

drift line = drifting longline.

drift maker = a person who made drift nets (archaic).

drift net = an unanchored gill net floating free with water currents or attached to a boat. Lost drift nets continue to catch and kill fish and marine mammals (called "walls of death") and large ones (50 km large scale pelagic driftnets) have been curtailed or banned on the high seas since 1991 by the Wellington Driftnet Convention and the 1993 UN General Assembly moratorium on large-scale drift nets. Also called drift gill net.

drift of fish = a concentration of cod (Newfoundland).

drift sinker = a lead weight that is attached to a fishing line and drifted, dragged or retrieved across the bottom. Available in various patterns.

drift sock = a large, sock-shaped, drift anchor.

drift-fish right = the allocation of the right to collect fish washed on shore, e.g. in 12 century Iceland where this fishery was crucial to survival in late winter when food supplies ran low and sea fishing was not possible because of the adverse weather conditions.

driftage = material that has been carried or deposited by a water current.

drifter = a vessel fishing with drift nets.

driftfood = drift food.

drifting fish aggregating device = natural or artificial free-drifting objects that attract pelagic fishes, such as tunas. Natural ones are logs and branches and objects of human origin such as oil drums and buoys. Artificial ones are deliberately constructed, such as bamboo rafts with purse-seine corks to aid in flotation and strength and with netting hanging down to act both as a drift anchor and as a concealment for smaller fishes. Artificial devices can have a radio or satellite-linked transmitting buoy so it can be located by fishers.

drifting longline = a longline kept near the surface or at a certain depth by means of regularly spaced floats. Drifting longlines may be of considerable length, and the snoods are usually longer and more widely spaced than for the bottom longlines. Some drifting longlines are set vertically, each line hanging from a float at the surface. They are usually worked in groups of several lines operated by a single boat. Also called drift line.

driftophagy = feeding on drift, e.g. Salmonidae.

drilled bobbin = a light-weight, hollow bobbin on the footrope of a bottom trawl with holes to allow flooding. Also called alloy bobbin.

drilling = mixing fish and salt by stirring in a trough so as to better incorporate the salt with the blood and juices (Scottish dialect).

drink like a fish = to drink too much alcohol.

drip = shrink (loss of weight in fish due to fluids draining from the food product. Also called purge).

drip bag = a device allowing the slow drip of pogey oil (q.v.) from a boat to attract fish.

drip incubator = an incubator used for water-hardened trout eggs where water drips from one tray to the next.

drip loss = liquid exuding from fish flesh when thawed.

dripping = draining surplus brine from a brined fish by leaving the fish hanging before smoking. Also called draining.

drive-in fishery = a net set usually in rocky or reef areas where active gear cannot be used, and/or where fish numbers entering passive nets is low, or where fish captured by a passive net would soon die as in tropical waters. Fish are driven into the net by various means such as beating the water with poles or using frightening lines (q.v.).

drive-in net = a lift net or pouch net into which fish are scared.

droch = droke.

drogue = 1) the British term for the American sea anchor, namely a drag, usually a canvas-covered conical frame, floating behind a vessel to prevent drifting or to maintain a heading into the wind.

drogue = 2) droke.

droke = a steep-sided valley with a small stream (Newfoundland). Also spelled droch, drogue (2) and drook.

dromous = running in a direction, used with prefixes for describing fish migratory habits, e.g. anadromous, catadromous.

droo = drew (1 and 2).

drook = droke.

drop back indicator = a device to detect a hooked fish swimming towards the angler - normally the line goes slack and the movement cannot be detected. The indicator can be electronic with a beeping alarm or a simple clip. The indicator is positioned on the rear bank stick and a free hanging open clip is hooked onto the line between the reel and the first rod guide. A fish swimming away from the angler pulls the clip up while one swimming towards the angler will cause the clip to drop down.

drop line = a handline used without a rod for catching fish.

drop loop = a high strength knot forming a loop off the main fishing line used to attach sinkers. Various websites have animated steps showing how to tie this knot.

drop shot = a hook tied directly to the fishing line from a few centimetres to a metre or more above the sinker. The hook is tied such that it is at a 90° angle to the line with the hook point up.

drop-net = 1) a net that catches fish by dropping, without being cast.

drop-net = 2) a modified fyke net used in winter.

drop-off = a rapid increase in water depth, an underwater precipice.

dropback = kelt (a spawned out or spent Salmo salar or other salmonid up until the time it enters salt water. A name used in British Columbia. Also called downriver).

dropline = a deepwater fishing method involving the use of a weighted vertical line bearing rows of baited hooks, operated by hand or by a mechanical device.

dropout = fish that fall out of a net while it is in the water or while it is being hauled in. The fish are often injured or dead and may be numerous.

dropper line = a short branch line from the main fishing line carrying hook and bait.

dropper loop = the knot forming a dropper line. A loop is formed above the sinker, standing out at right angles to the line. Various websites have animated steps showing how to tie this knot.

dropper shot = in angling, small lead weights spread out along the line between the hook and the float or hook and the bulk shot. They serve in bite detection as the float is very sensitive to any movement of the hook and bait.

dropshotting = a hook is tied on a line with a Palomar knot, the line looped through the eye from the top and, instead of being trimmed off, a section 6-24 inches long is left with a weight at the end. Looping the line through the eye leaves the hook point up. Also called downshotting.

dropsy = a swelling of the fish's body usually caused by bacterial infection, and also by viral infection, osmoregulatory problems, a flagellate protozoan (Hexamita), aggravated by poor environmental conditions. Serous fluid accumulates in any body cavity. Other symptoms are lethargy, gasping, increased respiration, colour loss, skin ulceration and exophthalmia. Also called pinecone disease and vertical scale disease because the scales stick out, and ascites.

drought = a collective noun (a noun that denotes a collection of persons or things regarded as a unit) for fishes.

drouth = to dry as in fish curing (Scottish dialect from English drought).

drowned = losing control of a fishing line so that is it is extended in a long curve, making it difficult to pull in a hooked fish (Scottish dialect).

drowned fish = dead fish; used of food fish discarded as unsuitable for sale.

drowned river = a former river inundated by a rise in sea level, now an estuary or covered by the sea.

drudge = 1) a drag-net used in fishing (Newfoundland).

drudge = 2) to catch herring (Newfoundland).

drudge = 3) to sprinkle salt on herring as a preservative (Newfoundland).

drudge bar = drudge barrow.

drudge barrow = barrow (a flat, rectangular wooden frame with handles at each corner, made for two men to carry cod. Also called fish barrow).

drum = 1) a fixed net, similar to a fyke net (q.v.) except that there is only one funnel leading to the codend and there are usually two wings. The net is usually checked several times a day by pulling up the drum section of the trap and emptying the fish from the codend.

drum = 2) a member of the drum of croaker family (Sciaenidae), named for the use of the swimbladder as a drum or resonating chamber to produce sound by the action of drumming muscles.

drum = 3) a cylindrical wooden container in which dried and salted cod from Newfoundland were packed for export to South America.

drum = 4) to pack dried and salted cod into a drum (Newfoundland).

drum = 5) a quantity of fish packed in a drum (Newfoundland).

drum fish = the quality of fish prepared for the South American market (Newfoundland).

drum gravity trap = gravity trap (a weighted cylinder that falls down and traps any fish pulling on a bait attached to a trigger mechanism).

drum muscle = one of the muscles attached to the gas bladder which makes the contained gas vibrate and emit a drumming sound. In pimelodid catfishes, for example, a muscle originates on the parapophyses of the 4 vertebra and sometimes too from the neurocranium and inserts on the ventro- and ventro-lateral surfaces of the gas bladder. Fish with drumming muscles also have a tensor tripodis, q.v., to reduce sound conduction to the inner ear See also drum, elastic spring mechanism and protractor post-temporalis mechanism.

drumming muscle = drum muscle.

drum seining = purse seining with shallow nets stored on, and paid out from, a powered drum at the stern of the vessel.

drum trap = a small fish trap in the shape of a cylindrical drum with entrance funnels, about 30 cm in diameter, made of local materials such as bamboo.

drum trawling = a trawl is paid out from a powered drum at the vessel stern.

drunk = it is illegal to get a fish drunk in Ohio according to state law.

drunk as a fish = very drunk.

drusel = to sprinkle salt on fish to keep them fresh while they are being gutted (Shetland Isles dialect).

dry = 1) the exposure of a split and gutted cod to sun and wind as part of a curing process. The process reduces natural moisture content.

dry = 2) try (to drain fish livers for oil).

dry bulk = dried and salted cod stacked in layers.

dry bundh = a shallow, seasonal depression bounded on three sides by embankments which captures monsoonal rain water.

dry caviar = caviar prepared in such a way that the eggs can be separated easily.

dry cure = to preserve cod by light applications of salt and through exposure to sun and wind.

dry curing = curing of fish by adding salt crystals.

dry deposition = a form of acid deposition (the addition of acidic material to the ground or water, usually from sulphur and nitrogen compounds emitted by factories and deposited far from this source, resulting from particle fallout or acidic gases. Wet deposition is also called acid rain, q.v., and is the result of rain, snow or fog).

dry fish = cod preserved by exposure to sun and wind after application of salt.

dry fly = a lure imitating an insect that floats on the water surface.

dry fly floatant = a chemical in aerosol, liquid or paste form applied to a dry fly to waterproof it.

dry off = to dry salted fish by exposure to the sun.

dry pile = split and salted cod placed in a stack towards the end of the curing process.

dry ration = air dried food made into particles suitable for feeding fish.

dry salted fish = fish cured by stacking split fish between layers of salt so that they drain freely. Used particularly with non-fatty fishes.

dry salting = salting (flavouring fish by rubbing in salt or by immersing the fish in brine for a short time before further processing such as smoking or canning. Also called salting or brining).

drying = the removal of moisture from fish by evaporation as a means of preservation; see dried fish. May be natural, taking place in the open air or over wood fires, or technological involving vacuum or freeze drying, for example. Often used in combination with salting and smoking.

drying beach = that part of a beach uncovered by water. Also called subaerial beach.

drying flake = an outdoor platform or rack for drying fish, q.v.

drying stage = a shed near the shore or built out over the water for landing, cleaning, salting and storing fish.

drying twine = drawing twine.

drying up area = drawing twine.

DS = abbreviation for dissolved solids (very small pieces of organic and inorganic material contained in water. Excessive amounts make water less habitable for fish, unfit to drink or limit its use in industrial processes).

DSL = abbreviation for deep scattering layer.

dual fin otter board = an otter board developed in British Columbia for midwater trawling using plywood sections to spread the trawl mouth.

dual purpose trawl = a trawl designed to fish on, and just off, the bottom.

dual purpose vessel = a vessel equipped to fish with two types of gear, e.g. seine and drift nets.

dubbing = fly tying material (strands of fur, plastic fibres, wool) wrapped onto a thread using wax and wrapped around the shank of a hook to imitate the abdomen and/or thorax of a fly.

dubbing rake = a tool used to tease out dubbing to give it an enlarged appearance.

dubious name = a name having uncertain application because it is impossible to establish the taxon to which it should be referred (nomen dubium).

Dubisch method = the design and construction of a Dubisch pond, named for its inventor.

Dubisch pond = a pond specially designed for spawning carp, which favour vegetation for egg deposition. Grass is grown to a height of about 40 cm on the pond bottom before water is added to the tip of the grass, and the spawning fish are introduced. A deep trench around the pond is where parental fish are kept.

Duchess Ann = a trout, named after the 17th century Ann, Duchess of Hamilton, who imported it from England to the Clyde River in Scotland. It is silvery, with bright scarlet spots and and grows to a large size.

duckbilled = a descriptive term for a snout that is shaped like a duck's bill, flattened and often concave in the upper outline, e.g. in the gobiid Anatirostrum profundorum or the pike Esox lucius.

duct = any tube-like structure.

duct of Cuvier = the common cardinal vein. The anterior cardinal vein returns blood from the head and the posterior cardinal vein from the trunk, joining together as the common cardinal vein (also called incorrectly the vitelline vein). The jugular vein from the lower jaw also empties into the common cardinal vein. The two common cardinal veins empty into the sinus venosus, q.v.

ductus communis = the tube into which several gill pouches open and which communicates with the exterior, e.g. in Myxinidae.

ductus Cuvieri = duct of Cuvier.

ductus endolymphaticus = a tube (endolymphatic duct) from the utriculus in the inner ear opening on the dorsal surface of the head in Elasmobranchii and terminating in the endolymphatic sinus in Teleostomi.

ductus pneumaticus = a tube connecting the pharynx to the gas bladder; pneumatic duct.

ductus semicirculares = semicircular ear canal (fluid-filled canals embedded in the cranium and concerned with balance and hearing. Gnathostomata have 3 canals, lampreys have 2 (lacking a horizontal canal) and hagfishes have only one canal).

duffy = a cod with a rounded or blunt head See also bulldog cod.

Duke's fish = a taboo name for salmon, as these were the property of the landowner, the Duke of Argyll (Scotland).

dull as a fish = very dull or uninteresting; not a condition subscribed to by ichthyologists.

dum(b) fish = dun fish (3).

dumb line = one of the ropes used to raise the cod trap door before the trap is hauled to the surface.

dumb string = end rope (a line connecting the end of the first or last section of a longline backrope or string to the dan line (all q.v.). Also called back of line, longline, dummy, end tow, lud tow and spreadline).

dumber than goldfish = dolphins; much of the large dolphin (and whale) brain is for insulation in cold water (Globe and Mail, 17 August 2006).

dummy = 1) the towpost amidships to which the warp is attached by a stopper when towing the trawl.

dummy = 2) end rope (a line connecting the end of the first or last section of a longline backrope or string to the dan line (all q.v.). Also called back of line, dumb string, longline, end tow, lud tow and spreadline.

dummy rock = a pierced rock attached to a longline to keep it down when fished from a dory (Canada).

dummy run = a partial migration of immature fish to spawning grounds, e.g. in some cod populations.

dumping = deliberate disposal of a catch that normally would be landed for sale. Fish are dumped because of quota closures, market saturation and high-grading, q.v.

dumpling = fish ball (fish don't have balls but are sometimes made into them. A ball of shredded white fish or cod and mashed potatoes, flour or other binding material, usually fried. Also called fish dumpling. See also catfish ball and ball).

dun = 1) an aquatic insect that has just emerged from the water and can fly.

dun = 2) a greyish or grey-blue colour in the wings of mayfly adults. Both terms are used in fly fishing as characters to imitate in making artificial flies.

dun = 3) a measure of the presence of the mold Sporendonema in commercial preparations of fish. Ranges from slight (barely visible) to moderate (less than 25% of the surface area).

dun = 4) a cure by slack salting (q.v.) of cod caught early in the spring, and often in February. Fish are laid in a pile for two or three months, in a dark store, covered, for the greatest part of the time, with salt hay or eel-grass, and pressed with some weight. In April or May they are opened and piled as close as possible in the same dark store, till July or August, when they are fit for use (New England).

dun fish = 1) cod with a brown discolouration caused by fungal growth (usually Sporendonema) on dried fish kept in damp conditions, poorly dried or stored.

dun fish = 2) fish prepared by the dun method (see dun (4)).

dun fly = an artificial fly used in angling.

duncan = a half-grown cod (Scottish dialect).

Duncan loop = in fly fishing, a knot used to attach a fly to the leader, leave the fly swinging freely or, if tightened, snug against the knot. Various websites have animated steps showing how to tie this knot. Also called a uni knot.

dundie = doondie.

dung worm = a worm or larva found in cow dung and used as bait for catching fish.

dunnage = dinnage.

dunning = dun (4).

duodenal vein = one of several veins draining capillaries of the duodenum adjacent to the gall bladder to the hepatic portal vein.

duodenum = an s-shaped loop of the intestine from the end of the stomach. The intestine continues as a straight section to the anus.

duration of ebb = the interval in which a tidal current is ebbing, determined from the middle of slack waters.

duration of fall =the interval from high to low water.

duration of flood = the interval in which a tidal current is flooding, determined from the middle of slack waters.

durken = said of fish that stop biting or are disinclined to bite (Scottish dialect).

durophagus = eating hard food such as mollusks, e.g. Chimaeridae.

Dutch aquarium = an aquarium where the plant species are of equal or greater importance than the fish. The plants may be arranged artistically and are the main aesthetic feature.

Dutch cured herring = herring gibbed (gills and intestine removed) and salted at sea and repacked ashore; not limited to the Dutch.

Dutch mess = salt cod and potatoes with browned onions. Garnished with scrunchions (the crunchy bits remaining after pork fat is rendered). Also called house bankin', fish and scrunchions or hugger-in-buff.

DWT = dressed or dressing weight, the weight of a dressed fish.

dyeing = 1) addition of an artificial or natural dye to fish before marketing, e.g. annatto, a yellow vegetable dye used to color fish before smoking, and amaranth a red dye used in fish roe.

dyeing = 2) addition of an artificial or natural dye to aquarium fish as a marketing ploy. Fluorescent dyes have been injected into glassfishes (Chandidae) and sold as "painted angels" or "disco fish". The painted areas fade and the fish are susceptible to skin lesions and kidney and liver damage, and have a shorter life span than normal specimens.

dyestuff = an indigestible pigment added to feed in aquaculture in order to monitor consumption of that feed through examination of stomach or faecal content.

dyke = dike.

dylox = 0-0-dimethyl-2,2,2-trichloro-1-hydroxy-ethyl phosphonate, an insecticide used in control of parasitic copepods. Also called dipterex and masoten.

dynamic lift = angling of the pectoral fins to create lift, as seen in sharks, which helps maintain position in the water. Requires that the fish keeps swimming.

dynamic pool model = analytical yield-per-recruit types of fisheries models describing how growth, recruitment and mortality interact, resulting in biomass and yields.

dynamite fishing = the use of explosives to kill and stun fish for capture. Used on coral reefs where nets cannot be operated without becoming tangled or ripped. Obviously illegal almost everywhere. Has been used by ichthyologists as a sampling method. Also called blast fishing.

dynnage = dinnage.

dyphyochiry = formation of the pectoral fins in two stages in Soleidae. The first, larval fins degenerate and post-larval fins are formed anew (from the French).

dys- (prefix) = abnormal, bad, insufficient, malfunction, difficult. Opposite of eu-.

dysphotic zone =the area in a water body without enough light for photosynthesis but enough for behavioural responses by the organisms living there (about 80-200+ metres). Also spelled disphotic.

dyssospondylous = referring to vertebrae in Amia, Lepisosteidae and Acipenseridae where the pleurocentrum, intercentrum, basidorsal, basiventral, interdorsal and interventral all ossify but remain independent in the embryonic and juvenile stages. Some elements fuse later and form vertebrae with two centra in the caudal region and typical vertebrae anteriorly.

dyssospondyly = the condition of a dyssopondylous vertebra.

dystrophic = 1) a type of lake in cold climates with low productivity, limited photosynthesis, scarce phytoplankton, carbon dioxide high and with hypolimnion oxygen depleted. Calcium, phosphorous and nitrogen scanty. Basin deep to shallow, found in boggy areas or mountains, with yellow to brown color and fairly abundant littoral vegetation. Generally transforms into a peat bog as organic materials accumulate because of only partial decomposition. Also used to refer to species inhabiting such lakes.

dystrophic = 2) pertaining to caves mostly supplied with vegetal matter during floods.

dystrophy = the dystrophic condition.

dz = doppel zentner (100 kg).

© Brian W. Coad (www.briancoad.com)

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