Dictionary of Ichthyology

Brian W. Coad and Don E. McAllister^†

Revised: 21 May 2008

E

E = abbreviation for exploitation rate (the proportion of a population at the beginning of a given time period that is caught during that time period (usually on a yearly basis). Also the ratio of fish caught to total mortality (= F/Z when fishing and natural mortality take place concurrently (Ricker, 1975)). Also called rate of exploitation).

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e.g. = abbreviation for exampli gratia, meaning for example.

e.p. = abbreviation for ex parte, meaning in part, partly.

e-type = a digital image of a holotype (Gewin, 2002).

EA = abbreviation for enterprise allocation, q.v.

Ea = a Sumerian fish god living in a submarine palace. Usually depicted as a man covered with a fish skin. Ea brought culture to mankind from the sea. See also apkallu fish and Enki.

eagle claw hook = a hook with the point curved inward in line with the eye; some varieties are double offset to the left and right.

eagre = bore (a rapid tidal rise in a river that forms an advancing wall of water).

ear = inner ear (the auditory organ lying in the otic capsule, consisting of the semicircular canals, ampullae, utriculus, sacculus, lagena, sinus endolymphaticus and ductus endolymphaticus. Filled with and surrounded by perilymph (or seawater in forms with an endolymphatic duct), containing otoliths (sagitta, astericus and lapillus in teleostomes). Functions as a gravity receptor, acceleration detector and muscle tone regulator. Innervated by cranial nerve VIII).

ear bone = earbone.

ear flap = a flattened, flexible structure extending back from the rear edge of the gill cover (operculum), e.g. in Centrarchidae. May be composed of skin or be supported by an extension of the operculum.

ear sac = branchial sac or gill pouch (the sac containing the gills and communicating with the mouth cavity and with the exterior in Myxini and Petromyzontiformes). Probably meant to be any pouch or sac surrounding the gills in fishes generally.

ear tab = ear flap.

earbone = used for earstone, incorrectly as it is not a bone.

earlier synonym = older synonym (an earlier synonym that cannot be used as the name for the taxon under the provisions of the International Code of Zoological Nomenclature).

early life history = the stages from egg to juvenile in development.

early mortality syndrome = large scale mortalities of introduced salmons in the Great Lakes just before yolk sac absorption. May be due to a vitamin deficiency.

earstone = otolith (a free calcium carbonate body in the inner ear used for perception of acceleration including gravity. The lapillus lies in the utricle, the sagitta in the saccule, and the asteriscus in the lagena. Also called statoliths or ear stones).

earth pond = earthern pond.

eartheater = taking mouthfuls of substrate with included food items and ejecting the debris, e.g. geophagine Cichlidae.

earthern 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 Danish pond.

earthy flavour = a tainted flavour or odour of fish flesh caused by the chemicals geosmin and 2-methylisoborneal released by microorganisms in the water and taken up by fish through their gills. These chemicals have very low detection thresholds, about 1 nanog/l. Found in fresh and brackish water fish as the responsible Cyanobacteria (Anabaena (geosmin) and Oscillatoria (2-methylisoborneal)) do not grow in sea water. Also called muddy flavour.

eastern shore boat = a smaller version of the Tamcook boat (q.v.) about 28-32 feet long with a crew of two. Used in Nova Scotia.

eat the rocks = said of cod schooling in large numbers near rocky shores in pursuit of capelin (Newfoundland).

eating fish = salt cod kept for home consumption (Newfoundland).

eats no fish = a trustworthy man; an honest man; not a papist (Protestants in the reign of Queen Elizabeth I refused to eat fish on Fridays to show they were not Catholic).

ebb = 1) a falling or receding tide, a tide between a high water and the succeeding low water. Flow exits an estuary during ebb tide.

ebb = 2) a part of the shore between high and low water marks assigned to individual fishermen (Scottish dialect).

ebb current = the movement of a tidal current away from shore or down a tidal stream.

ebb interval = the interval between the transit of the moon over the meridian of a place and the time of the following strength of ebb.

ebb stel = a fishery involving a stel carried out on an ebb tide.

ebb strength = the ebb current at the time of maximum velocity.

ebb tidal delta = the sand bar formed at the seaward mouth of tidal inlets as a result of the meeting of tidal currents and waves.

ebb tide = ebb. Strictly, a non-technical term.

Ebisu = one of the seven Japanese Gods of Happiness, the protector of fishermen, symbolised by an angling rod and a large fish held in his hand.

eccentric = 1) off centre, deviating from the usual.

eccentric = 2) said of dictionary compilers.

echelon trawl = an experimental form of otter trawl with a large upper wing and paravanes instead of doors. Meant for use in bottom fishing and midwater herring fishing.

echo signature = a unique sonar return or reflection that can be used to identify individual species of fish.

echo sounder = a sonar device that sends a signal to the bottom of a body of water and back. Used to detect fish schools and to map the bottom as an image is displayed on a screen. Used in angling, it is also called a fish finder.

eclosion = the process of hatching from an egg.

eco-label = a label placed on commercial products to indicate that environmentally friendly methods have been used in its capture and preparation.

eco-port = a port that allows ships to discharge waste in an ecologically sustainable manner.

ecocline = gradual and continuous change in environmental conditions of an ecosystem or community.

ecodeme = a population occurring in a specified kind of habitat.

ecological drainage unit = a drainage that differs from adjacent ones in fauna and physiography.

ecological extinction = a fish population where numbers are too few to maintain their role ecologically.

ecological niche = the place of an organism in its biotic environment; the position or function of an organism in a community of plants or animals; anthropomorphically speaking, its occupation. A microhabitat.

ecological resilience = the ability of an ecosystem to absorb change. See also resilience.

ecological reserve = an area zoned to protect the living resources through prevention and prohibition of fishing and the disturbance of the living and non-living resources.

ecology = the science of the role played by the environment in the life of an organism; the interrelationships between organisms and their environment. It deals with the role of the environment in determining what organisms will be present.

ecomorph = a local population or group whose appearance is determined by ecology, e.g. lake ecomorphs are deeper bodied than river ecomorphs. Not of systematic or taxonomic significance.

economic discard = a fish thrown overboard in a commercial fishery for economic reasons, e.g. too small, damaged, not enough commercially value, etc.

economic efficiency = the point at which the added cost of producing a unit of fish is equal to what buyers pay. Producing fewer fish would bring the cost lower than buyers are paying. Producing more fish would raise the cost higher than buyers are paying. Harvesting at the point of economic efficiency produces the maximum economic yield. A measure of the efficiency of input producing output.

economic overfishing = occurs when a fishery is generating no economic rent (higher than economic efficiency), primarily because an excessive level of fishing effort is applied in the fishery. Does not always imply biological overfishing.

economic production = the catching of a great a quantity of fish of as high a commercial value as possible.

economic rent = the total amount of profit that could be earned from a fishery owned by an individual. Individual ownership maximizes profit, but an open entry policy usually results in so many fishermen that profit higher than opportunity cost is zero.

economic zone = exclusive economic zone, q.v.

economically healthy fishery = a fishery that supports the fishers, their gear and the improvement of gear and techniques.

ecophenotype = a phenotype showing adaptations associated with the habitat or environment that are not genetic.

ecospecies = a group of related ecotypes that exchange genes without loss of fertility; roughly the same as a taxonomic species.

ecosystem = the complex of living organisms and environmental conditions that function as a unit. Biocenosis plus biotope.

ecosystem overfishing = occurs when the species composition and dominance is significantly modified by fishing, e.g. with reductions of large, long-lived, demersal predators and increases of small, short-lived species at lower trophic levels.

ecotone = the boundary or transition area between two or more habitats or communities.

ecotope = the abiotic or non-living part of an ecosystem.

ecotype = a population adapted to a restricted habitat as a result of natural selection within a local environment. Nothing to do with taxonomy.

ectad = outwards, towards the exterior.

ectethmoid = parethmoid (a paired deep bone lying in the front of the orbit under the prefrontal).

ecto- (prefix) = outside, outer, external.

ectocommensal = a commensal that lives on the surface of the host.

ectocoracoid = a paired dermal bone in Gasterosteiformes connected with the coracoid and extending posteriorly. Has also been applied to the element below the scapula and applied to the coracoid in Dipnoi.

ectogenic meromixis = the mixing of lake water as a result of some outside agency, e.g. influx of saline water.

-ectomy = surgical removal, e.g. ovariectomy, removal of the ovaries.

ectoparasite = an external parasite, on fishes often lice or leeches. Also includes parasites found in the gill cavity.

ectopterygoid = a paired, deep, dermal bone forming part of the roof of the mouth, articulating anteriorly with the palatine, posteriorly with the quadrate and mesially with the endoptetygoid if the latter is present. In Amia it has one or two rows of teeth. Sometimes called pterygoid when there is no endopterygoid.

ectotherm = an organism with a body temperature determined by the environment; poikilotherm; cold-blooded.

eddy = a circular movement of water where currents flow counter to each other or pass obstructions.

edema = a swelling; abnormal accumulation of serous fluid in the interfibrillar spaces of connective tissue. Also spelled oedema.

edentate = toothless.

edentulate = toothless.

edentulous = toothless.

edge = a term for a change in the structure, conditions or vegetation in a lake or other water body. Edges can be weed lines, drop-offs, temperature areas, water clarity, current, etc. Fish are often found at such edges, actively feeding.

edge type = a deposition found on the outer edge of a scale, otolith or other ageing structure representing the most recent growth.

edible fish = fish than can be eaten; suitable as food, usually in the commercial sense.

edible weight = the weight of a fish after removal of bones, guts, etc.

edition = all the copies of a publication printed at the same time (but not an unaltered reprint).

education collection = a group of museum specimens for use in an educational programme. These may have fewer restrictions on handling than most museum specimens, may not be catalogued in the permanent collection of the museum and may be discarded when damaged or no longer required.

eel = 1) a general tem for any fish with an elongate body. Strictly, a member of the Order Anguilliformes with over 790 species world-wide, mostly in shallow marine waters. Most terms mentioning eels in English are referring to Anguilla anguilla, the European eel, and sometimes to Anguilla rostrata, the American eel. Lamprey-eel is a mis-nomer as lampreys are not eels. Lampreys (Petromyzontidae) are sometimes referred to as eel-shaped but eels could more correctly be termed lamprey-shaped on an evolutionary basis.

eel = 2) a Japanese flavour of ice cream, made with many others in response to a hot summer in 2004. See also saury and brandy, and shark fin and noodle.

eel ark = a device or trap for catching eels (Scottish dialect).

eel ascending ramp = part of an eel ladder, this ramp has structures against which the eels can push to ascend. The ramp may be simply a hollowed out tree filled with old fish nets or a commercial product made of plastic with an undulating surface and studs.

eel basket = a basket trap, q.v., for catching eels.

eel bed = 1) a pond for eels.

eel bed = 2) a swampy bivouac.

eel blobbing = catching eels with eel spears.

eel bob = a special bait, or bob made to catch eels by bobbing, q.v.

eel buck = a large basket used to catch eels. Also called buck.

eel comb = eel rake.

eel drowner = a clever person as they can perform the impossible; used ironically and negatively (Scottish dialect).

eel fare = 1) the passage of young eels upstream.

eel fare = 2) a brood of eels.

eel Florentine = a dish made of skinned and headed eels, cut into pieces, sprinkled with salt, pepper and olive oil, refrigerated for two hours, then coated with bread crumbs, oil is heated in a casserole, garlic is sauteed, sage and eel pieces are added in a single layer, and baked at 350ºF for 40 minutes.

eel fork = an Asian hooked device with one or two sharp prongs thrust into mud to catch eels, the fisherman being on foot or operating from a boat.

eel graip = a small fork used for digging up or spearing sandeels (Scottish dialect).

eel grate = 1) a kinnd of trap placed in a mill race to catch eels (English dialect).

eel grate = 2) catching eels with a spiked pole or stang.

eel hook = eel fork.

eel knife = a knife specialised for splitting an eel lengthwise.

eel ladder = a fish ladder designed to help eels over dams and weirs. A substrate is provided for the eels to push against when slithering upstream. A fish elevator may be part of the process at high dams. See also eel ascending ramp.

eel muggie = a fish stomach used as a container for eel fat (Scottish dialect).

eel pick = a form of spear used for catching eels.

eel pie = a pastry pie containing eels. The eels have their head, tail and skin removed, are sliced into segments and placed in the bottom of a pie dish with chopped onion and parsley and seasoned with salt, pepper and nutmeg. A stock may be made by soaking the skinned eels in water with the heads and tails. Eel sauce is then made with melted butter, flour and eel stock, thickened and lemon juice added, before pouring into the pie and serving hot.

eel pot = a trap to catch eels, usually a basket trap.

eel rake = a comb or rake-like implement used in eel fishing. Also called eel comb.

eel rhabdovirus = viruses isolated from European and American eels, relationship to each other or to other rhabdoviruses unknown.

eel shot = the first fish caught and gutted on New Year's Day (Scottish dialect).

eel skin = 1) the skin of an eel. See also eelskin, eelskins.

eel skin = 2) a tight-fitting dress or other garment. See also eelskin, eelskins.

eel spear = a pronged device for spearing eels.

eel tow = a line laid inshore for catching eels for bait (Scottish dialect).

eel tongs = ridged metal tongs with long wooden handles used to pick up slimy, slippery and muscular eels.

eel tuft = a small bundle of brushwood, several of which my be tied along a line. They are about 1 metre in length and resemble brooms; fish hide in these structures and can be caught when they are rapidly pulled from the water or scooped with a net. Used to catch eels, burbot and possibly lampreys in Europe.

eel virus = an orthomyxovirus-like organism isolated from European eels with stomatopapilloma although relation to latter unknown.

eel weel = eel buck.

eel wheel = eel buck.

eel-backed = horses having black stripes along their backs.

eel-like = similar to an eel, usually meaning eel-shaped.

eel-shaped = elongate body form as in eels, e.g. Anguillidae. Lampreys (Petromyzontidae) are often referred to in this fashion although eels should be called lamprey-shaped.

eeler = a fisher for eels.

eelery = an area devoted to the raising of eels.

eelgrass = a submerged aquatic plant (Zostera marina) of the North American Atlantic coast with very long and narrow leaves.

eelgrass meadow = an extensive bed of eelgrass, an important marine habitat for fish, but ca. 90% has been destroyed along the North American coast.

eeling = catching or fishing for eels.

Eels = 1) a nickname for New Englanders in the 1830s, a tribute to their fondness for eels.

Eels = 2) an American rock band formed by singer and songwriter Mark Oliver Everett.

eelskin = a fine leather made from the skin of hagfishes (Myxinidae). See also eel skin.

eelskin wallet = wallets made of electric eel skins were said to demagnetise credit cards, a popular myth. The wallets were made from hagfish skin. Magnetic metal clasps may have played a part.

eelskins = tight trousers (slang). See also eel skin.

eely = eel-like.

EEZ = exclusive economic zone, q.v.

effective concentration = the concentration of a substance in water needed to produce a specific effect to a portion of test animals, e.g. EC₅₀ is the concentration producing an effect in 50% of the test fish.

effective fishing effort = fishing effort, e.g. hooks per day, adjusted or standardised, when necessary, so that each increase in the adjusted unit causes a proportional increase in instantaneous rate of fishing. Controls purported to limit effective effort imply that the fishing mortality rate is to be limited. Abbreviated as F/q, F/q, f or f.

effective publication = publication in accordance with the requirements of the International Code of Zoological Nomenclature.

effective rainfall = the portion of total rainfall that reaches rivers and lakes.

effectiveness of fishing = the percentage removal of fish from a stock, but not specifically defined as either rate of exploitation or instantaneous rate of fishing.

efferent = leading away from.

efferent branchial arteries = those arteries paralleling the afferent branchial arches (q.v.) and joining to form a left and right root or radices of the dorsal aorta.

effluent = 1) that which flows out or forth, especially a stream flowing out of a body of water.

effluent = 2) wastewater such as that from a fish farm, municipal sewage plants, pollutants, and coolant waters from a nuclear power plant.

effluent stream = gaining stream (a stream or a part of a stream where flow increases because of groundwater discharge).

efflux = flowing out, that which flows out.

effort = 1) the total fishing gear in use for a specified period of time; when two or more kinds of gear are used, they must be adjusted to some standard type before being added.

effort = 2) effective fishing effort, abbreviated as f or f (Ricker, 1975).

effort = 3) the amount of time and fishing power used to harvest fish. Fishing power includes gear size, boat size, and horsepower. May be expressed as days away from port, hours trawling, length of drift net, etc.

effort = 4) a measure of resource use by anglers, e.g. number of angler hours, party hours, boat hours, trips on the water. Also called fishing pressure.

effort control = 1) a measure applied to effort used by managers to regulate fishing.

effort control = 2) limitations on gear and time used rather than on catch limits as a means of managing a stock.

effort restriction = a type of input control used as a management tool whereby the amount of fishing effort expended by fishers in a particular fishery is restricted by law or voluntary agreement among fishers who jointly exploited fishery resource. In practice, as fishing effort is a composite index of various elements, e.g. fishing craft, gear and ancillary equipment, fishing time, etc., it has proven to be difficult to effectively contain its growth in the medium and long term.

EFL = eye-fork length, q.v.

EFZ = exclusive fishing zone, q.v.

egesta = food or waste products eliminated from an organism, including bacteria and mucus.

egestion = the production of egesta.

egg = 1) a fish egg, varying in size from under 1.0 mm to 6.0 mm or more, and of various colours.

egg = 2) a simple type of fly tied in imitation of a fish egg from yarn, usually orange or pink, and fished along the bottom.

egg case = the keratinous egg shell of Myxini, Elasmobranchii and Holocephali containing the developing embryo.

egg dummy = an egg-like spot, e.g. on the anal fin of mouthbrooding Cichlidae. The male cichlid displays these spots to a female who sucks at the spots assuming them to be real eggs; the male releases sperm that fertilise the eggs in the mouth of the female. Also called egg spots or false eggs.

egg layer = the usual mode of reproduction in fishes where eggs are laid outside the body and fertilised there by the male.

egg lobe = egg ribbon.

egg loop = a special knot used to attach a leader to a hook, specifically designed to hold roe bait.

egg mass = eggs that have been laid in a large amount or clump.

egg pincette = small tweezers or tongs with cup-shaped tips, used to pick out defective eggs in hatcheries trays.

egg pit = the pit in a redd where the female deposits one batch of eggs.

egg pouch = egg sac.

egg production method = a means to estimate spawning biomass of fish by a probe attached to a plankton net. The probe measures temperature and depth at which the eggs were collected and thus allows extrapolation to the total spawning biomass in the area under study.

egg raft = a supporting structure of various shapes and dimensions which carries eggs, e.g. in Histrio and Antennarius.

egg ribbon = long, ribbon-like (2 m by 8 cm) egg masses, some with a central cavity, found in certain fish species, e.g. Perca flavescens.

egg sac = the envelope enclosing the ova of a fish.

egg scooper = a small scoop or tray with a vertical handle, allowing transfer of eggs in hatcheries, e.g. to incubator trays.

egg shell = chorion (an embryonic membrane, elaborated by the follicle cells, which encloses the egg. The eggs of truly viviparous fishes are non-chorionated. Usually hardens on contact with the water; after fertilization the egg secretes fluid and shrinks inward leaving a perivitelline space. May lie external to the zona radiata. Called egg shell in fish).

egg sinker = a type of weight used in angling and shaped like an egg with a hole through the middle. Used in still water and for rolling in current.

egg size = the greatest diameter of a spherical egg, both the length and width of elongate or elliptical eggs.

egg sorter = a worker in a processing plant packing Pacific salmon eggs for export.

egg spot = egg dummy.

egg stealer = a fish that feeds on the eggs of other fishes by stealing them from a nest site, e.g. the Lake Malawi cichlid Otopharynx ovatus.

egg survey = the abundance of eggs and larvae in an area, determined by sampling with appropriate gear, e.g. small meshed midwater trawls, plankton nets, bamboo traps. Used to estimate the size of the spawning stock and/or the importance of spawning.

egg take = the number of eggs taken at hatcheries when adult fish are spawned.

egg viability = the ability of an egg to develop normally.

egg weight = egg-shaped lead weights with a hole through their middle used in angling. The line runs freely through the hole and when a fish takes up the bait and runs, it feels little resistance.

egg yolk = the yellow part of an egg containing proteins to nourish the embryo and larva.

egg-bearing season = that period of a year when a female fish is carrying eggs.

egg-capsule = egg-case.

egg-carrying = attachment of eggs to a fish for incubation, e.g. in Kurtus gulliveri (Kurtidae) where egg masses are attached to the male supraoccipital hook.

egg-case = the keratinous egg shell of Myxini, Elasmobranchii and Holocephali containing the developing embryo.

egg-laying = the process of depositing eggs.

egg-laying area = that part of the bottom or other structures where eggs are deposited.

egg-strand = the elongate, hollow, cylindrical structure produced by Perca fluviatilis containing eggs which is twisted around plants and logs.

egg-to-smolt survival = the numerical difference between the number of fertilized eggs produced by a groups of fish and the number of smolts resulting from those eggs.

eggs-per-recruit = an index of abundance, the average number of eggs produced by a fish that has been recruited (moved into a spawning or fishing-size class).

Egtved disease = an acute or chronic disease of salmonids, such as rainbow trout in farm ponds, causing loss of appetite and of schooling behaviour, darkened colour, bleeding, hyaline gills and exophthalmia. It is associated with temperature changes and with the late winter and spring seasons when temperatures are below 8°C. Abbreviated as VHS. Also called viral haemorrhagic septicaemia and trout pest.

eicosapantaenoic acid = an omega-3-fatty acid, q.v., found in fish oil; its chemical name is all-cis-5,8,11,14,17-icosapentaenoic acid. Said to reduce the risk of heart attacks in humans when ingested at 1800 mg per day. Also called icosapentaenoic acid and timnodonic acid. Abbreviated as EPA.

eight-angle net = two boat lift net (a large coastal Japanese lift net, with or without wings, operated from two boats and set against the current. May be operated in the day but at night, additional boats with lights are used to attract fish).

eight boat lift net = a coastal Japanese lift net about 200 m in circumference laid on the sea floor by eight boats in an area where fish are expected to pass over it. When a spotter determines fish are over the net it is lifted so that fish are driven to one corner. Used to catch mackerel and sardines. See also two boat, three boat and four boat lift nets.

einstein = a gene name for a zebrafish mutation affecting the ear (one otolith at all stages). See also half stoned, what's up, rolling stones, van gogh, among many others.

EIS = abbreviation for Environmental Impact Statement.

Ekman circulation = movement of surface water at an angle from the wind as a result of the Coriolis effect.

Ekman layer = the thin horizontal layer of water riding on top of the ocean that is affected by wind.

El Niño = abnormally warm ocean climate conditions, which in some years affect the Eastern coast of Latin America (centred on Peru) often around Christmas time. The anomaly is accompanied by dramatic changes in species abundance and distribution, higher local rainfall and flooding, massive deaths of fish and their predators including birds.

elaborate = highly developed, unusual, specialised, said of structures or colours of fishes.

élangueur = a piece of wood used to keep the mouth of fish open while the hook is removed in longlining for cod (Canada).

elasmobranch poisoning = poisoning resulting from eating the flesh or viscera of sharks and rays. Poisoning from shark flesh is generally mild while that from shark liver may result in severe effects such as nausea, vomiting, diarrhoea, abdominal pain, headache and prostration, leading to coma and even death. Treatment is symptomatic, no antidote is known.

elasmoid scales = cycloid and ctenoid scales, q.v.

elastic = a mechanism used inside fishing rods in Europe. An elastic is threaded into the top three sections of a rod, anchored inside, fed out through a protective bush at the rod tip, and the line tied to the end. Elastic is pulled out by a hooked fish but cushions any run by the fish, helping in fighting and landing the fish. The elastic retracts into the rod when the fish stops running or is unhooked. Elastics come in various strengths from 1 (smallest) to 20 (largest), the diameter increasing with size. PTFE bushes are used internally or at the point the elastic emerges from the rod tip. These polytetrafluoroethylene bushes have a very low friction level and protect the elastic from wear.

elastic cartilage = cartilage containing elastin fibres as well as collagen and having a yellowish appearance.

elastic spring mechanism = a structure consisting of thin spring-like modified portions of the parapophysis of the 4th vertebrae (Müllerian process) which are attached to the skull by muscles and to the gas bladder. When the muscles contract and relax, the resultant vibrations in the gas bladder produce a growling sound, e.g. certain Clariidae and other catfish families. See also Müllerian process and Müllerian protractor. See also drumming muscle and protractor post-temporalis mechanism.

elasticity = very fresh fish have elastic flesh; when depressed by a finger, the depression quickly disappears.

elastoidine = a scleroprotein of which the ceratotrichium, q.v., is composed.

elastotrichia = a kind of elastic fin ray.

electivity index = an index (E) showing the degree of choice a predator shows in its feeding behaviour, e.g. of a predator on plankton; E is derived from r_i - p_i / r_i + p_i where r_i is percent composition of plankter i in the gut contents and p_i is percent composition of plankter i in the plankton sample. Values for E range from -1 to +1 with -1 meaning complete avoidance, 0 meaning no active selection, and +1 meaning complete selection.

electric fish trap = a large wire mesh cage with an open top having electrodes at the mouth. Fish are attracted by electrotaxis to the electrodes and stunned, falling into the trap.

electric fishes = fishes which give out electric currents, e.g. Electrophorus, Torpedo, Mormyrus, based on electric organs. These may be weakly discharging used for orientation and prey detection in murky conditions or strongly discharging and capable of stunning prey and predators.

electric organ = the structure capable of emitting electrical discharges through the surrounding water and which may be used to stun prey, to repel predators or as a radar-like device to detect objects under conditions of poor visibility, e.g. Torpedo, Malapterurus, Electrophorus, Gymnarchus, Mormyrus, Astroscopus.

electric screen = a series of electrodes strung across a waterway to prevent passage of fish, to direct fish into a trap or into a fish pass.

electric smoking = fish smoked by hanging on a two-line wire used as an electrode.

electric tuna hook = an electrified hook which stuns the tuna.

electrical fence = electric screen.

electro-fishing = an electric current will result in fish orienting themselves to the anode and swimming towards it involuntarily thus facilitating capture.

electro-narcosis = immobility as the muscles slacken when electro-fishing.

electro-sensing = the ability of certain fishes to sense electric currents, e.g. sharks.

electro-shocker = a device generating an electrical current used to paralyse or kill fish and facilitate their capture. See electro-fishing.

electro-trawl = a trawl with electrodes in front of the trawl mouth to attract and stun fish.

electrocution = a method of killing fish with electricity to ensure a high quality and appearance.

electrocutor = electro-shocker.

electrocyte = electroplax.

electrogenic = capable of generating electric currents and a painful electric shock, e.g. Electrophorus, Mormyrus, Torpedo.

electrogenesis = the production of electric currents and a painful electric shock.

electrolocation = the ability to use electrical fields to locate objects.

electronic bite alarm = a battery powered device which detects line movement in angling, emitting a buzz or beep and a small light. Often used in ledgering.

electronic nose = a device that analyses vapours close to a product as a measure of quality, rather as a nose can detect different odours. The device has to be trained, e.g. for detection of freshness in a particular species of fish. Not yet in use commercially. Also called artificial nose.

electrophoresis = the movement and separation of chemicals in a fluid medium under electrical stimulation. Used to determine the chemical content of fishes and other organisms and thereby to distinguish and relate them.

electroplaque = electroplax.

electroplate = electroplax, q.v.

electroplax = a disk-like multinucleate cell, numbers of which form electric organs. The electric eel has a stack of several thousand of these cells, each producing 0.15 volts. Also called electrocytes, electroplaques or electroplates.

electroreception = the ability to make and receive electrical impulses and use these to distinguish objects by the different resistance and capacitance values. Fish can communicate by modulating the electrical waveform they generate. Fish may use active electroreception, generating small, usually less than one volt, electrical pulses using an organ in the tail consisting of two to five rows of modified muscle cells called electrocytes. This has a range of about one body length. Fish can also use passive electroreception where the fish senses the weak bioelectric fields of other organisms. This is found in sharks, for example, using the ampullae of Lorenzini, q.v.

electroreceptor = an organ which detects the presence of an electric current. They are particularly receptive to their own electrical fields and can detect perturbations caused by other fishes and objects. Found, for example, on such weakly electric fishes as mormyrids and gymnotiforms. Also called tuberous organ or receptor.

electroshocker = electro-shocker.

electrostatic smoking = electrically charged smoke particles rapidly deposited on a fish.

electrotaxis = orientation to electric currents. When exposed to a direct electric current from a fish shocker, fish tend to assume a position parallel to the current with the head towards the positive pole or anode. Also called galvanotaxis.

elementary population = a population of fish in the same biological condition, usually of the same age and with the same biological processes.

element = a unit of some larger structure, e.g. a ray or spine of a fin.

elements = the constituent parts that fall within the limits of a taxon, e.g. species within a genus.

eleutheroembryo = an embryonic phase starting with hatching and ending when most or all of the yolk is absorbed and the fish starts feeding, or until feeding on ovarian secretions ends at birth.

elevate = elevation in rank or taxonomic status, e.g. from subspecies to species.

elevated scale = a scale higher than wide, usually said of anterior flank scales and of the exposed portion of the scale.

elevation = fish elevation (the elevation of a fish above the stream bed measured at the tip of the fish's snout).

elevation in rank = change the standing of a name in nomenclature; the change in position of a name in a taxonomic hierarchy, e.g. from subspecies to species.

elide = to deliberately omit one or more letters within a word.

elimination, fixation by = fixation by elimination (the supposed fixation of a type species by the subsequent transfer of all but one of the originally included nominal species from a genus. Not in itself an available method of type fixation).

elittoral = the sea bed zone below the sublittoral down to the limit of light penetration; the sea bed below 40 metres.

ellis = fish brine. Also spelled alex or alix. See also alec.

elongate = of lengthened slender form; longer than deep, e.g. Anguillidae, Stichaeidae.

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

elver = young transparent, cylindrical transformed Anguilla about 5-8 cm long, at the stage in their migration where they have reached the coasts and begin ascending rivers and have lost the leaf-like leptocephalus form. Also called glass eel.

emaciation = excessive leanness or wasting of body tissue.

emarginate = having an edge slightly concave; shallowly forked (particularly of caudal fin); indented.

embankment = 1) a raised bank confining a river.

embankment = 2) the act of making an embankment.

embayment = 1) an indentation of the shoreline forming a bay.

embayment = 2) formation of a bay.

embedded = enveloped in skin, lacking free edges, e.g. scales of Zoarcidae, Anguillidae

embeddedness = the degree to which dirt or finer material is mixed in with spawning gravel.

embolism = gas bubble disease (supersaturated gases (>115-125%) in water entering the the body fluids of fish causing bubbles, an embolism. Often seen in gills, eyes, skin and yolk sacs where membranes are the most gas permeable. Fish often swim upside down or vertically, sometimes looking as if they are gasping for air at the surface and may have exophthalmia. Found below power plants in winter when cold water is rapidly heated by passing through condensers, in hatcheries using borehole water and in aquaria when fresh cold water is rapidly heated. Also called air embolism).

embouchure = the mouth of a river or stream.

embryo = developmental stages to the moment of hatching or of birth. Fish have endogenous nutrition from yolk, or via a specialised absorptive organ depending on ovarian secretions, or via a combination of both these methods.

embryon = embryo.

embryonal stage = pertaining to different stages of fish development in the egg.

embryonate = an egg containing an embryo.

embryonic axis = an elongate thickening of blastoderm tissue; the primitive differentiation of the embryo.

embryonic cannibal live bearer = a reproductive guild (q.v.) where only one or a few eggs from the ovary develop into a juvenile. Other yolked ova are fed on by the juveniles as ovulated (oophagy) or less developed embryos are eaten by the more developed ones (adelphophagy). There is specialisation for intrauterine respiration. The largest gain in weight is during intrauterine development, e.g. Carcharias taurus.

embryonic coprophagy = excretion of yolk glycoproteins from the gastrointestinal tract of the embryo to the perivitelline space where they are swallowed by the embryo, e.g. in Neogobius melanostomus.

embryonic period = the time from union of gametes (or in gynogenetic fishes the triggering of cell division) until exogenous nutrition. This period is characterised by endogenous nutrition from the yolk of the ovum (or in viviparous fishes from an ovarian secretion or combination of yolk and secretion). This period is divided into three phases:- cleavage (beginning of development to beginning of organogenesis), embryonic (organogensis) and eleutheroembryonic (hatching to external feeding after all or most of the yolk is absorbed).

embryonic shield = a thickened arm of the germ ring representing the future longitudinal axis of the embryo.

emend. = abbreviation for emendatus. The abbreviation precedes the name of the author effecting the change in a scientific name.

emendation = in nomenclature, any demonstrably intentional change in the original spelling of an available zoological name, other than a mandatory change; a name of which the spelling has been altered. Does not include emendation of the scope of application of a name, which equals an emended diagnosis (q.v.). Emendations may be correct or incorrect, depending upon whether the changes are in accordance or not with the International Code of Zoological Nomenclature. A justified emendation is the correction of an incorrect original spelling (and takes authorship and date of the original spelling). An unjustified emendation is any emendation other than a justified emendation (the emended name is treated as a new name with its own authority and date).

emendatus = emended or altered (by); used where the author has changed the original spelling of a taxon without excluding the type of the name. Abbreviated as emend.

emended diagnosis = change in the scope of application of a name, involving a change in the diagnosis (q.v.) of the taxon. Not the same as emendation (q.v.).

emerge = 1) hatch from an egg.

emerge = 2) come up out of the water (as in hatching insects).

emergence = departure of fry from the gravel into the water column.

emergence trap = a device for trapping fish (and insects) as they emerge from the gravel into the water column.

emergent vegetation = plants growing in water but emerging from it, usually at the water's edge.

emerger = 1) a stage in the life cycle of an aquatic insect when it swims to or near the surface to hatch, changing from a nymph or pupa to a winged adult. Fish may concentrate to feed on emergers.

emerger = 2) an artificial fly tied to imitate an emerger by anglers.

emersed vegetation = emergent vegetation.

emigration = the movement of individuals out of a population or from one are to another.

Emperor's pike = an Esox lucius reputedly caught in a lake in Württemburg in 1497 with a copper ring around the gill region. The ring bore an inscription intimating that the pike had been placed in the lake by Emperor Frederick II in 1230, making the pike 267 years old. A nineteenth century study of the skeleton of this fish preserved in Mannheim Cathedral showed it to have more vertebrae than a single pike should have and the story is considered a fake.

empty-gutted = fish without food in the intestine.

emulsion = a fertilizer emulsion produced from the liquid remains of processed fish in fish meal and oil industries.

EN = endangered, q.v.

en tresse = a platted fillet where the backbone and bones are removed leaving the fillets attached to the head.

enamel = a shiny hard material covering the dentine of teeth and the surface of some scales (cosmoid and placoid scales). This is the hardest substance produced by vertebrates. Of ectodermal origin, produced by ameloblasts. Consisting of crystals of a calcium phosphate-carbonate salt (apatite) cemented in an organic matrix.

enameloid = a mesodermal derivative laid down at the outer surface of mesodermal papillae as a form of bone with greater density and mineralisation than dentine. Found in the scales of Palaeozoic fishes as a superficial layer over a dentine structure.

encapsulated egg = an egg contained in either a thick horny, or thin membranous case, e.g. Elasmobranchii.

encircling gillnet = used in shallow water with the floatline remaining at the surface; after the fish have been encircled by the net, noise or other means are used to force them to gill or entangle themselves in the netting surrounding them.

enclosed sea = a gulf, basin, or sea surrounded by two or more States and connected to another sea or the ocean by a narrow outlet or consisting entirely or primarily of the territorial seas and exclusive economic zones of two or more coastal States.

enclosure = a fence or barrier which encompasses or shuts in fish.

encounter rate = encounters per unit of gear per unit time.

encounters = the numbers of a species that are caught by fishing gear but are released voluntarily or by regulation.

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, dummy, end tow, lud tow and spreadline.

end tow = end rope.

endangered = said of a taxon facing imminent extirpation (nationally) or extinction (world-wide). In the IUCN Criteria for threatened species, a taxon is Endangered when it is not Critically Endangered but is facing a very high risk of extinction in the wild in the near future. Abbreviated EN.

endangered collection = a collection of museum specimens that may be lost to the scientific community as it is no longer or soon may be of no interest to its current owner. See also orphan collection.

endemic = restricted to a certain region; peculiar to; native to.

endemic centre = an area having a unique fauna, often classified as an area with five of more endemic species.

ending = the termination of a scientific name. The letters at the end of genus-group name must be, or be treated as, a singular name in the nominative case which indicate the gender of the word. The letters at the end of an adjectival species-group name which must agree in gender form with the gender of the generic name with which the species-group name is combined. The letters at the end of a species-group name which, if the name is the genitive case of the name of one or more persons, or a place, or other entity associated with the taxon, form the genitive case and reflect the gender and number, e.g. -i if of a man, -ae if of a woman, -orum if of women, (or men and women together), -arum if of women. The letters at the end of the genitive case of a generic name which are deleted to form a stem, before adding a suffix to form a family-group name.

endless trolling line = a slowly moving looped trolling line. The line is carried down to a specific depth, returned to the surface, passes over the vessel so that the catch can be removed and hooks re-baited, and then on down again.

endo- (prefix) = within, inside, inwards, inner.

endobenthic = living within the sediment of a lake or sea floor; infauna. Also called endobiontic.

endobiontic = endobenthic.

endocast = a cast of the interior of a structure, e.g. part of a fossil showing the lumen of the gut.

endochondral = refers to skeletal elements which are formed in cartilage and which later ossify. Also called replacement bone because it gradually replaces the pre-existing cartilage.

endocranium = that portion of the neurocranium consisting of the elements surrounding the olfactory, optic and otic capsules and the anterior end of the notochord.

endogenous feeding = a type of nutrient acquisition during fish ontogeny, usually from yolk but also from a maternal-embryonic exchange. See exogenous and absorptive feeding.

endolateral circumorals = large teeth immediately on each side of the mouth opening in lampreys (Petromyzontidae). Also called endolaterals.

endolaterals = endolateral circumorals.

endolymph = the watery fluid in the membranous labyrinth of the ear.

endolymphatic duct = a tube from the utriculus opening on the dorsal surface of the head in Elasmobranchii and terminating in the endolymphatic sinus in Teleostomi. Also called ductus endolymphaticus.

endolymphatic pore = the external opening of the endolymphatic duct.

endolymphatic sinus = a chamber at the outer end of the endolymphatic duct in Teleostomi.

endoparasite = an internal parasite, e.g. the fish Carapus apus living in the body cavity of holothurians and feeding on the gonads and water lungs. But see also inquiline.

endopsammic = living on the surface of sand.

endopterygoid = metapterygoid (the deep, paired, endochondral bone forming the posterior end of the palatoquadrate and connected with the hyomandibular. Absent in many modern Teleostei, it bears teeth in the Albulidae. Also called mesopterygoid and entopterygoid).

endoreic = endorheic.

endorheic = said of an area where rivers arise but do reach the sea, drying up or terminating in a closed basin.

endoskeleton = the skeleton proper; the inner bony support for the body.

endostyle = a longitudinal ciliated groove on the ventral wall of the pharynx which produces mucus to gather food particles in Amphioxi and the ammocoete stage of Petromyzontiformes. In the latter it changes during development into the thyroid gland. Also called hypopharyngeal groove.

endozooic = living inside an animal, e.g. carapids in echinoderms.

English knot = fisherman's knot (a knot for tying the ends of two lines together. Various websites have animated steps showing how to tie this knot).

English shore = that area of the coast of Newfoundland where the English had fishing and curing rights; originally from Cape Bonivista to Trepassey. The extent varied with the vagaries of fortune (cf. French shore).

engrailed = 1) indented along an edge with small curves. Opposite of invected.

engrailed = 2) having a margin or edge of small raised dots.

engulfer = a piscivore that swallows prey whole.

engybenthic = pertaining to organisms near the benthos.

engyodontic stage = an early stage in an anguilliform larva characterised by few, needle-like teeth, upper and lower jaws of equal length, an undifferentiated finfold, no nasal capsule, no hypurals, straight notochord tip, and the head and preanal region of the body relatively large. Precedes the euryodontic stage.

enhaline = salinity approximating sea water. See also ensaline.

enhancement = release of fish from an aquaculture facility to increase the size or growth of a wild fishery or other stock. The releases may be fry or older fish.

enhancement programme = a stock enhancement program to enhance or increase the size or growth of the fishery resource stock.

enkan-hin = shioboshi (whole or split fish dried after soaking in salt water or dry salt (Japan). Usually the name of the fish used is appended).

Enki = the Sumerian god of water, his symbols being a goat and a fish, later combined as a single beast, the Capricorn, which became one of the signs of the zodiac. See also Ea.

enmesh = to catch, entrap or entangle fish in the mesh of a net.

enrichment = addition of nitrogen, phosphorous and carbon compounds or other nutrients into a water body. This increases the growth of algae and other aquatic plants. Enrichment often results from the inflow of sewage effluents or from agricultural run-off, or may be deliberate to increase productivity in aquaculture.

enrobing = coating (fish products may be marketed with a coating, e.g. of batter and breadcrumbs).

ensaline = salinity approximating sea water. See also enhaline.

ensiling = preservation of dead fish, offal and wastes from an aquaculture facility in an acidic medium.

entad = inwards, towards the centre or interior; internally.

entamoebiasis = an infection with protozoans of the genus Entamoeba.

entangling net = a vertical gill or trammel net that is hung loosely such that fish become entangled rather than gilled.

enteric redmouth disease = a systemic bacterial disease caused by Yersinia ruckeri found mostly in salmonids. Symptoms are severe congestion, septicaemia and haemorrhage in head tissues such as the palate and operculum with the lower jaw being eroded. Internal organs can also be infected. Abbreviated as ERM. Also called Hagerman redmouth disease.

enteric septicaemia = a disease caused by the bacterium Ewardsiella ictaluri affecting fingerling and yearling catfish. Characterised by a raised or open ulcer on the frontal bone, hence the alternate name of hole-in-the-head disease.

enteritis = a bacterial disease, possibly Aeromonas punctata, causing an expanded abdomen with red blotches, fins are congested, the anus is red and swollen, pressure on the belly causes a yellow mucus discharge from the anus, the intestinal wall is inflamed and peels off. The fish shows loss of appetite, swims slowly and alone, and death results.

entero- (prefix) = the intestine.

enterprise allocation = a quota from a particular fishery stock allocated to one company operating more than one vessel. Must be fished during the year allocated although timing is up to the company and the allocation can be transferred to another company. Abbreviated as EA.

entire = smooth edged; lacking serrations or spines.

ento- (prefix) = within, inner.

entopterygoid = 1) metapterygoid (the deep, paired, endochondral bone forming the posterior end of the palatoquadrate and connected with the hyomandibular. Absent in many modern Teleostei, it bears teeth in the Albulidae. Also called mesopterygoid and endopterygpoid).

entopterygoid = 2) tooth-bearing plates flanking the parasphenoid in certain Sarcopterygii.

entrained = pulled along by a current.

entrainment = 1) the incidental trapping of fish in intake water used for cooling electrical power plants, in waters being diverted for irrigation, or in any artificial construction.

entrainment = 2) the synchronisation of one biological rhythm to another.

entrapment gear = any fishing gear that traps fish; may be fixed or movable but all have some means of preventing the fish escaping once they enter the trap.

enumeration = the act of counting fish returning to spawn.

enveloping layer = the outermost layer of cells surrounding the embryo that become very flattened in the blastula and give rise to the periderm.

envenomation = to sting or to impregnate an organism with a toxin by means of a venom apparatus (a tooth or spine with poison gland or poisonous tissue).

environmental disease = a disease in fish caused by an unfavourable environment, e.g. lack of oxygen, temperature variations.

environmental gill disease = swollen gills caused by an irritating pollutant.

Environmental Impact Statement = a document prepared to describe the effects of proposed activities (such as implementation of a fisheries management plan) on the environment. Impacts can be positive or negative or both and the document may also describe ways to mitigate impacts.

environmental resistance = the difference between the potential ability of a population to increase and the actual observed performance.

environmentally sustainable fishery = a fishery that sustains all parts of the ecosystem and does not cause any long-term or permanent change.

enzootic = a disease present in organisms all the time but in small numbers of individuals at any one time (equivalent to endemic in humans). See also epizootic.

Eocene = a geological epoch within the Tertiary Period ca. 54-38 million years ago.

epal = relating to the upper gill arch, e.g. epibranchials, hyomandibula, palatoquadrate. Compare ceratal.

epaxial = any structure morphologically dorsal to the horizontal plane of the notochord or vertebral column; body muscles above the horizontal septum.

ephemeral = 1) short-lived, transitory.

ephemeral = 2) used to refer to streams which flow only in direct response to precipitation and whose channel is at all times above the water table.

ephemery = a descriptive term for the life cycle of tadpole gobies (Benthophilus spp.) which live about a year, attain maturity at 6-7 months, and die after spawning.

epi- (prefix) = upon, on the surface of, above.

epibaseost = the distal pterygiophore articulating with the dorsal and anal fin rays.

epibatic = said of a caudal fin with the upper lobe longer.

epibenthic = located on the bottom or floor of a water body, rather than in the bottom.

epibiont = an organism that lives on the outside of another organism.

epibiontic = living attached to another organism without benefit or detriment for the host.

epiblast = the outer of two layers of the blastoderm that form during gastrulation. Corresponds to the primitive ectoderm during gastrulation and to the definitive ectoderm after gastrulation.

epiboly = the thinning and spreading movement of the embryonic cell mass over the surface of the yolk, eventually encompassing the yolk completely.

epibranchial = a deep cartilage bone on the upper part of the gill arch below the uppermost element, the pharyngobranchial. May occur on arches 1, 2, 3, 4 and be covered with toothed pads.

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.

epicaudal lobe = a median terminal lobe of the caudal fin characteristic of coelacanths.

epicentral = a short, rod-like bone attached to the centrum of the anteriormost vertebrae, e.g. Merluccius has 3-4 pairs.

epicercal = a caudal fin with the upper lobe the longer, upwardly tapering, with the skeletal elements forming the upper margin of the fin. Also called heterocercal but this perhaps applies to both epicercal and hypocercal (lower lobe longer).

epicontinental = found in or on a continent or continental shelf. Epicontinental seas abound in fishes.

epidemic spawning = simultaneous shedding of gametes by a large number of individuals, such as the whole population, so chances of fertilisation are high.

epidermis = the outermost of the two layers of the skin. Of ectodermal origin and comprising 4-6 cell layers in Elasmobranchii and 10-30 in Teleostei. In Cyclostomata the epidermis secretes a thin acellular cuticle also seen in some Teleost pearl organs. Overlies the dermis.

epifauna = animals living on the surface of the bottom or floor of a water body. Does not include organisms burrowing into the floor but does include those organisms living on others.

epigean = surface dwelling, as opposed to hypogean, ipogean or "cave" fishes.

epigenetic = all processes relating to the expression and interaction of genes.

epigonal organ = an elongate paired tissue ventral to the kidneys and partially enveloping the anterior gonads in Elasmobranchii. Apparently important to the immune system.

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 dorsal ceratohyal or posterohyal 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.

epilimnion = the warm uppermost layer of water in a stratified lake, above the thermocline.

epimandibular cartilage = palatoquadrate (the cartilaginous, functional upper jaw of Elasmobranchii and Holocephali and the embryonic upper jaw of other gnathostome vertebrates. In adult Dipnoi, Crossopterygii and Actinopterygii, produces the autopalatine, metapterygoid and quadrate bones. Also called palatoquadrate or palatoquadratal bar, palatoquadrate cartilage, pterygoquadrate bar, epimandibular cartilage and maxillar cartilage).

epimeralium = epineural.

epineural = a slender bone which lies in the myocomma and projects backwards and upwards from the neural arch and spine. Epineurals may be forked.

epioccipital = epiotic, q.v.

epiotic = the deep bone and the superficial bone overlying it which form the upper element of the otic capsule, and lie posterior to the parietal, ventral to the supraoccipital, and dorsal to the pterotic. It covers the posterior semicircular canal. It is considered to be an ossification of the occipital arch that has invaded the otic region and so is often called epioccipital.

epipelagic = pertaining to the relatively well-lit, warm and blue water of the ocean from the surface down to a depth of about 200 metres.

epiphysial apparatus = consists of two median dorsal projections from the diencephalon - an anterior parietal body and a posterior pineal body or epiphysis. These bodies are light sensitive and influence the melanophores and the behavior of the animal.

epiphyte = organisms growing on or associated with the substrate.

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 with the vertebra, e.g. in Gobiidae. Also called dorsal rib and intermuscular bone.

episom = epaxial.

episternal = urohyal (a flat, median, deep, endochondral bone below the ceratohyal; a tendon bone arising in the septum between the longitudinal muscles of the isthmus. Absent in such primitive fishes as Lepisosteus. Also called clidost, interclavicle and parahyoid).

"epistylis" = red sore disease (a disease caused by a ciliated protozoan (Epistylis and Heteropolaria spp.) exhibiting as ulcers or cotton-like growths on the skin, scales and fin spines causing a red lesion, and also found on eggs).

epitegum = a shield element of jawless fishes, e.g. the ventral shield is considered as a single epitegum.

epithelial fringe = oral fimbria (one of a series of small tag-like appendages around the perimeter of the oral disc of lampreys (Petromyzontiformes), presumed to help create an effective seal when the lamprey is attached to its host and also probably sensory. Also called fringed processes, leaf-like processes, fringed lappets, leathery appendices and leathery appendages).

epitheliocystis = a chlamydial infection of fishes that may show no symptoms or exhibit as respiratory distress. Numerous white cysts develop on the gills and skin.

epithelioma papulosum = carp pox (one of the oldest known fish diseases found in cultured carp, other cyprinids, pike-perch and aquarium fishes. It is caused by Herpesvirus cyprini. Also known as carp papillomatosis, epithelioma papulosum, fish pox, cyprinid herpesvirus I (CHV). Skin lesions appear as the water temperature drops in winter as small milky-white spots that merge and cover large skin areas).

epithet = the second word of a binomial name of a species (or the second and third of a subspecies); specific name; trivial name.

epitheta hybrida = epithets made up of parts of words from two or more different languages.

epitheta specifica rejicienda = rejected specific epithets.

epizootic = a disease attacking many animals in a population in a short time. Equivalent to epidemic in humans. See also enzootic.

epizootic ulcerative syndrome = an epizootic in freshwater and estuarine fish of warm waters. It is characterised by an invasive Aphanomyces infection and ulcerative lesions.

epontic - referring to organisms closely associated with sea ice, attached, in interstices between ice crystals, or within channels in sea ice where some fish may be found.

eponym = named for a person, e.g. Glyptothorax silviae (Sisoridae) named for Sylvie Coad but note that the Latin origin of the name forms the root for the eponym.

eptatretin = a potent cardio-stimulant obtained from the branchial heart of Eptatretus stouti (Myxinidae). The substance is reported to be a highly unstable aromatic amine.

epural = an elongate detached bone above the urostyle and behind the last neural spine supporting caudal fin rays. Apparently derived from neural spines or the urostylic centra; dorsal homologues of the hypurals. Vary in number between one in advanced fishes to three in primitive actinopterygians.

equal = the same, said of jaws of the same length.

equatorial current = 1) ocean currents flowing westerly near the equator. There are two in each of the Atlantic and Pacific oceans, one north of the equator (the North Equatorial Current) and one south (the South Equatorial Current) separated by the easterly flowing Equatorial Countercurrent.

equatorial current = 2) tidal currents occurring semi-monthly as a result of the moon being over the equator.

equatorial tide = a tide occurring semi-monthly as a result of the moon being over the equator.

equilibrium = when fishing and natural mortality, exploitation pattern, growth and recruitment do not change from year to year; when such factors have been in effect long enough to affect all ages for the whole exploited life. Also called steady state.

equilibrium catch = the catch (in numbers) taken from a fish stock when it is in equilibrium with fishing of a given intensity, and (apart from the effects of environmental variation) its abundance does not change from one year to the next. Also called sustainable yield, equilibrium yield. Abbreviated as CE or C_E.

equilibrium yield = the yield in weight taken from a fish stock when it is in equilibrium with fishing of a given intensity, and (apart from effects of environmental variation) its biomass is not changing from one year to the next. Also called sustainable yield, equivalent sustainable yield. Abbreviated as YE or Y_E. No stock is really in balance with fishing effort because effort cannot be maintained at the same level and the stock is always changing in response to environmental variables.

equivalent sustainable yield = equilibrium yield.

erect = establish or coin, as for a scientific name.

erectile = capable of being lifted upright.

erisma = the fused first two proximal pterygiophores; long and well-developed in Solea.

ERM = abbreviation for enteric redmouth disease, q.v.

err. typogr. = abbreviation for errore typographico, meaning typographical error, q.v.

erratic parasite = a normal parasite in an unusual location.

error = an incorrect spelling in a name, or other word. A copyist's error is an incorrect spelling made in copying, an inadvertent error is an incorrect spelling, such as a lapsus calami, or a copyist's or a printer's error, not intended by the original author, and a printer's error is an incorrect spelling made in type-setting (often called typographical error). Such errors may have significance in nomenclature.

errore typographico = typographical error.

eructation = burping, belching or ructus is the release of gas from the digestive tract. In fishes this may be from the vent, or from the gas bladder connected to the gut via the pneumatic duct, and thence the mouth. Some eructations may be just emptying the gas bladder but others appear to be a deliberate sound production as it does not vary over time, e.g. in certain eels and catfishes.

erythrism = a red or orange pigmentation seen in aquarium fishes, e.g. orange swordtail (Xiphophorus helleri) and the in nature, e.g. the cichlid red devil (Amphilophus labiatus).

erythro-melaniridosomes = association of erythrophores, melanophores and guanophores.

erythrocyte = red blood cell.

erythrodema = a bacterial infection (Pseudomonas fluorescens) usually through lesions found in major carps. Symptoms include inflammation bleeding from the skin, loss of scales, bloodshot fin bases, fraying of fins, red blotches around the mouth and occasionally congestion and inflammation of the intestines.

erythroiridosomes = association of erythrocytes and guanophores.

erythrophore = a chromatophore exhibiting red (or orange) color. Contains a carotenoid pigment.

esca = the specialized lure on the outer end of an illicium. Sometimes luminous, worm-like or fish-like in form, e.g. in Ceratioidei.

escabèche = a cold marinade made of olive oil, vinegar (or citrus juice) and spicy herbs. Used to preserve cooked foods such as small fish which are headless, fried or lightly browned and marinated for a day. Served as an hors d'oeuvre. The word is Spanish in origin or possible from the Farsi sikbag meaning acid food.

escapee = specimen of a cultured species that escapes from an aquaculture facility. It may carry diseases or parasites or interbreed with wild stock.

escapement = number of migratory fish that reach a favourable spawning area annually. Refers to the fish that pass through a fishing area unscathed and reach the spawning grounds; usually said of anadromous fish.

escapement curve = the relationship between size (or age) and the probability of a fish escaping from the gear after having encountered it, e.g. swimming through the mesh of a net, the sorting grid of a trawl, or the escape gate of a trap. Sometimes called selectivity curve.

escapement goal = a predetermined, biologically-derived number of salmonids that are not harvested and will be the parent spawners for a wild or hatchery stock of fish.

esociform = pike-shaped.

esophagus = that tubular portion of the gut between the pharynx and the stomach. Also spelled oesophagus.

Esox epidermal proliferation-associated virus = virus-like particles found in epidermal lesions in northern pike (Esox lucius).

Esox lymphosarcoma-associated virus = a leukovirus-like agent isolated from pike with lymphosarcoma but relationship to latter unknown.

essence d'Orient = silvery crystals of guanine in scales which are extracted and used to make a pearl essence for artificial pearls.

essential fish habitat = any habitat that is of basic importance to the survival and well-being of a fish population or community, either a habitat used throughout life or for a specific activity such as spawning or feeding.

establish = to publish a zoological name so that it is available in the meaning of the International Code of Zoological Nomenclature, or make available (a name that was previously unavailable) for whatever reason.

established = successful growth and reproduction in a given area, usually in terms of an introduced population.

established species = valid species (a species that has an existence in the real world and is recognised as such. In opposition to a species thought to be distinct but which does not actually exist, is no longer recognised, or is treated as a synonym). May be confused with the usage of established for an introduced species, and a valid species could be ignored and therefore established is inappropriate.

establishment = the business, and all its parts, of a fish merchant (Newfoundland). Usually refers to the branch of a firm with headquarters in St John's, Newfoundland or Britain.

estero = a lagoon with greater salinity at its head than its mouth, since evaporation exceeds precipitation there. Found on desert margins of the American southwest and in Mexico. Also called a negative estuary.

estimated discard mortality = the numbers of fish thrown overboard that die, calculated by observers and from logbook records.

estivation = dormancy during the dry season. e.g. in Dipnoi. Also spelled aestivation.

estuarine (adjective) = condition in that portion of a river, the estuary, where it meets the sea and fresh and salt waters mingle or alternate.

estuarine dependent = fish and other organisms that live in estuarine conditions for all or part of their lives.

estuary (noun) = see estuarine.

esu = an evolutionary significant unit; a segment of a species defined as important in survival and conservation of the species such as a specific spawning run of a salmonid.

et(t) = said of fish ready to take the bait, either individually or in a school (Scottish dialect).

et = and; used to connect names of authors after the scientific name. Often "and" or & is used.

et al. = abbreviation for et alii meaning "and others"; used in author citations where the initial author's name is followed by et al. to indicate there are more authors.

etc. = abbreviation for et cetera, meaning "and so on".

ethanol = C₂H₅OH; used as a 70-80% solution in water for the permanent preservation and storage of fish specimens in museum collections. Also called ethyl alcohol, grain alcohol or spirit of wine.

ethyl alcohol = ethanol.

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 and dermethmoid.

ethmoid gland = a gland in the ethmoid bone associated with the ethmoid tooth in Monognathidae. Possibly secretes poison.

ethmoidea = plural of ethmoideum.

ethmoideum (plural ethmoidea) = ethmoid.

ethmosphenoid = part of the cranium in front of the intracranial joint in Crossopterygii; behind it is the otico-occipital portion.

ethology = the study of innate behavior; of behaviour in the normal environment of the fish (although often carried out in a simulated environment, the aquarium).

ethyl alcohol = ethanol, q.v.

etymology = used in taxonomy for the derivation and meaning of a scientific name.

eu- (prefix) = good, well or stable. Opposite of dys-.

euabyssal = waters of the sea below about 4000 metres.

euautostylic = a jaw suspension in which the jaw is attached directly to the braincase, e.g. in Placodermi.

euhaline = 1) living only in saline inland water bodies.

euhaline = 2) waters containing between 30 and 40 parts per thousand of dissolved salts, i.e. in most cases, normal sea water.

euhyostylic = condition of the palatoquadrate when it is supported only by a stout hyomandibular and is unattached to the neurocranium. The ceratohyal in euhyostyly is widely separated from Meckel's cartilage.

eulachon oil = oil extracted from Thaleichthys pacificus (Osmeridae) in British Columbia and used to flavour foods by native peoples.

eulittoral = the marine intertidal zone subject to wave action; the shore of a lake between high and low water marks.

eupelagic = organisms in open ocean water away from the sea bed.

euphotic zone = the surface waters of the sea or of a lake where enough light penetrates for photosynthesis to occur, down to about 80 metres.

euphysoclistous = having the gas bladder closed, with no connection to the gut.

eupotamic = pertaining to organisms equally capable of living in still or flowing fresh water.

European gill rot = branchiomycosis (a disease caused by the fungi Branchiomyces sanguinis and B. demigrans found particularly in carp and eels. Respiratory distress is caused by gill necrosis as blood vessels thrombose. Gills become discoloured in patches and rot. Occurs in ponds with high temperatures, excess organic matter and high ammonia levels. Also called gill rot).

eury- (suffix) = wide or broad. Opposite of steno-.

eurybaric = tolerant of pressure, hence depth changes. Opposite of stenobaric.

eurybasal = having a wide fin base, e.g. in Dipnoi. Opposite of stenobasal.

eurybathic = tolerant of a wide range in depth.

eurybenthic = living on the lake or sea floor over a wide range of depths.

euryhaline = 1) organisms capable of withstanding a wide range of salinity.

euryhaline = 2) water with a salinity of 30.1-40.0 p.p.t. derived from ocean salts.

euryodontic stage = an advanced stage in angulliform development characterised by three series of relatively short, broad teeth, a relatively shortened lower jaw, the formation of nasal capsules, fins and hypurals, flexion of the notochord and a relatively smaller head and preanal region. Follows the engyodontic stage.

euryokous = adapted to numerous ecological niches. Opposite of stenokous.

euryphagous = feeding on a wide variety of foods.

eurysaline = 1) organisms capable of withstanding a wide range of salinity.

eurysaline = 2) water with a salinity of 30.1-40.0 p.p.t. derived from land-derived salts.

eurythermal = organisms capable of withstanding a wide range of temperature.

eurythermic = eurythermal or pertaining to or living in water of wide temperature range.

eurythermos = able to tolerate wide variations of the temperature in the environment.

eurytopic = having a wide range of geographical distribution.

eurytropical = occurring throughout the tropics.

eustasy = worldwide simultaneous change in sea level.

eustatic = rise in sea level relative to the exposed land still depressed after melting of the glaciers.

eutrophic = adjective for eutrophy.

eutrophication = the deterioration of the life-supporting features of a lake or estuary caused by excessive pollutants or fertilisation from effluents high in phosphorus, nitrogen and organic growth substances. More decomposing organic matter is produced by the excessive growth of algae and plants than self-purification processes can overcome. It is also the natural aging process of a lake, leading to its disappearance as plants and sediments fill it in.

eutrophy = the condition of a lake which is highly productive and hence the hypolimnion becomes depleted of oxygen (through decay of organic products). Usually having a shallow wide basin with coloured water and abundant littoral vegetation.

euxinic = an environment lacking oxygen and with very little water circulation. From Pontus Euxinus, the Black Sea in reference to the anoxic conditions at depth.

evacuation zone = the anterior-ventral region of the mid- and late gastrula that becomes poorer in cells as they leave by epiboly and convergence.

evanescent = temporary, disappearing.

even-year run = a population of fish that returns to its natural spawning grounds in even numbered years.

evening hatch = the emergence of aquatic insects in the evening; emergence is the transformation of an insect from a swimming to a flying stage at the water surface; a term used by anglers. Hatches attract fish.

evenness = the distribution of abundance such as biomass or individuals among the species within an assemblage.

everglade(s) = marshland covered with grass in places and usually having water.

eversible = adjective for evert.

evert = turn inside out, disgorge; used of guts protruding from the mouth of a fish brought up quickly from depth when the swimbladder expands and pushes internal organs out, and of the lips in kissing gouramies (Helostoma temminckii, Helostomatidae).

eviscerated = said of fish having at least the gut and sometimes all the internal organs removed.

evo-devo = an abbreviated form for evolutionary developmental biology.

evolution = descent with modification.

evolutionarily significant unit = a population or group of populations inhabiting a defined geographical area that comprises a unique segment of the species; a distinct population, reproductively isolated from other conspecific populations and is an important evolutionary legacy of the species. Abbreviated as ESU. An ESU is often treated as a "species" in conservation assessments.

evolutionary significant unit = evolutionarily significant unit.

evolutionary developmental biology = an integrated approach to explaining biodiversity, taking into account molecular genetics through embryology, molecular and population genetics, comparative morphology, palaeontology, molecular evolution, ecology and functional morphology. It analyses interactions between development and evolution.

evolutionary tree = a diagram depicting the hypothetical phylogeny of the taxa under consideration. The points where lineages split represent ancestor taxa to the descendent taxa at the terminal points.

EW = extinct in the wild (in the IUCN Criteria for threatened species, a taxon is Extinct in the Wild when it is known only to survive in cultivation, in captivity or as a naturalised population (or populations) well outside the past range. A taxon is presumed extinct in the wild when exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range have failed to record an individual. Surveys should be over a time frame appropriate to the taxon's life cycle and life form).

EX = extinct (in the IUCN Criteria for threatened species, a taxon is Extinct when there is no reasonable doubt that the last individual has died).

ex = from, according to. Sometimes used within an author citation, q.v.

ex aff. = abbreviation for ex affinis, meaning of affinity.

ex affinis = of affinity.

ex gr. = abbreviation for ex grupo, meaning of the group of.

ex grupo = of the group of.

ex nomine = by or under that name.

ex parte = in part.

ex situ conservation = conservation of species or populations outside their natural area of distribution or habitats, cf. in situ conservation.

ex-collection = collection to which a museum specimen formerly belonged.

ex-vessel = refers to activities that occur when a commercial fishing boat lands or unloads a catch. For example, the price received by a captain (at the point of landing) for the catch is an ex-vessel price.

ex-vessel price = the value of fish at first sale by fishermen at the dock, distinguished from wholesale or retail value.

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

exapt = adaptation by selection to a different purpose, e.g. the buoyancy function of the swimbladder was exapted as a respiratory organ in some fishes.

excess capacity = in the short-term, fishing capacity or number of boats that exceeds the capacity required to capture and handle the allowable catch. In the long-term, fishing capacity that exceeds the level required to ensuring the sustainability of the stock and the fishery at the desired level. Excess capacity is the difference between current fishing capacity and target fishing capacity (Yc – YT)/YT, in which Yc is current yield or catch and YT is target yield or catch (to be evaluated and compared relative to the same stock size). Also called over-capacity, excess harvesting capacity.

excess fish = the number of hatchery-reared fish that return to their hatchery without being caught.

excess harvesting capacity = harvesting capacity in excess of the minimum or least cost amount needed to harvest the desired quantity of fish.

exchange = specimens sent to another museum for a similar number of different specimens to enhance both institutions' collection diversity or to further research interests of the scientists involved.

excised = margin cut out, concave.

excisura major = the notch in the margin of the fish otolith separating the rostrum and antirostrum.

excisura minor = the notch in the margin of the fish otolith separating the postrostrum and pararostrum.

excl. = abbreviation for exclusus, meaning excluded. Used to indicate those components included in a given taxon by one author but excluded by the present author.

excl. gen. = abbreviation for excluso genere, meaning with the genus excluded.

excl. spec. = abbreviation for exclusa speciei, meaning with the species excluded.

excl. specim. = abbreviation for exclusis speciminibus, meaning with the specimens excluded.

excluded = 1) said of a work, name or act which is to be ignored for purposes of zoological nomenclature either under the provisions of the International Code of Zoological Nomenclature or because of a disclaimer.

excluded = 2) denoting a specimen or component which has been explicitly omitted or removed from a type series or a name-bearing type.

exclusion zone = an area where fishing or even passage is not allowed, e.g. around historic wreck sites, oil and gas installations.

Exclusive Economic Zone = waters out to 200 nautical miles (370.40 km) from shore where international waters begin. Reserved to that country for exploitation and management of resources. Also called the 200-mile limit. Abbreviated as EEZ.

Exclusive Fishing Zone = the exclusive fishing zone out to 200 nautical miles, replaced by the EEZ. Abbreviated as EFZ.

exclusive rights = the right to catch fish exclusive to the holder(s) of the right, i.e. the holders can exclude others without the right from catching fish in the fishery.

exclusus = excluded, used to indicate elements included in a taxon by a previous author or authors, but considered not to belong to it by the writer and excluded from it by him. Abbreviated excl.

excreta = faeces, urine.

exemplar = a random sample of a taxon.

exethmoid = parethmoid (a paired deep bone of perichondral origin lying in the front of the orbit under the prefrontal. Also called pleurethmoid, prefrontal, exethmoid and, incorrectly ectethmoid, as this latter is only in birds).

exhalent chamber = branchial chamber (the cavities in which lie the gills).

exhibit collection = museum specimens on display in a public exhibit. The specimens may be designated specifically for the exhibit and thus may be discarded when the exhibit is closed, or stored separately from the main collection. Specimens from the main or permanent collections may be used in exhibits but do not from part of an exhibit collection.

existence value = the economic value of knowing that a resource exits, whether or not there is the ability to use that resource now or in the future.

exit fishery = a fishery directed at a transient phase in the life cycle, e.g. only the juveniles of a species.

exoccipital = a deep, paired, endochondral bone at the posterior end of the cranium on each side of the foramen magnum, often bearing articular facets for the first vertebra.

exocrine pancreas = a well-defined organ which secretes enzymes into the digestive tract by means of a duct.

exogenous feeding = nutrient acquisition during fish ontogeny by food taken in through the mouth and digested in the intestine. See endogenous and absorptive feeding.

exolaterals = small teeth between the endolaterals (near the mouth opening) and the marginals (which line the margin of the disc) in lampreys (Petromyzontidae).

exophialiasis = infection with the fungi Exophiala salmonis and E. pisciphila, of particular importance to cage-cultured salmonids. The fish become lethargic, darken, and occasionally dermal nodules develop. Yellow to white granulomas are found in the viscera.

exophthalmia = protrusion of the eyeballs (plural of exophthalmos).

exophthalmos = protrusion of an eyeball. Usually results from liquid or gas accumulation at the rear of the eye socket or by diseases. Also called popeye.

exophthalmus = exophthalmos.

exorheic = an area where rivers rise and flow to the sea.

exoskeleton = hard parts on the body surface developed in the dermis, called membrane or dermal bones (scales, scutes, spines, plates, elements of the head and pectoral girdle, etc.). In bony fishes, many of these bones migrated to deeper layers below the dermis, forming a secondary exoskeleton.

exotic = not native; introduced from a foreign place or country. Exotics are usually from a completely different fauna and may carry diseases and parasites which native fish have no resistance to, be major predators on native species, or compete for habitat and food.

expanded feed = in aquaculture, a type of food composed of low-density pellets that sink slowly. May be used to produce diets high in oil. See also extruded feed.

expatriate = an individual of a species which has been transported to an area in which it cannot reproduce and from which it cannot return except by chance, e.g. the myctophid, Lobianchia dofleini, in the western Atlantic.

expatriation = the process of expatriating or removal by an agency, such as a current to an environment in which it cannot reproduce and from which it returns only by chance.

expatriation area = an area in which a species cannot reproduce or return from and is present in only through reinforcements from another area.

expedition = 1) an extended fishing trip.

expedition = 2) an investigation made with the hope of discovering information but without any clear evidence at hand when begun.

expendable bathy-thermograph = an instrument that records water temperature with depth. Abbreviated as XBT.

experimental fishing = fishing with new gear to test its effectiveness and its effect on fish stocks.

expiscation = an elucidation or investigation, literally a "fishing out".

exploitable age = any age of fish in a fishable stock.

exploitable biomass = refers to that portion of a stock's biomass that is available to the fishing gear.

exploitation pattern = the distribution of fishing mortality over the age or length composition of the fish population, determined by the type of fishing gear, area and seasonal distribution of fishing, and the growth and migration of the fish. The pattern can be changed by modifications to fishing gear, e.g. increasing mesh or hook size, by changing the ratio of harvest by gears exploiting the fish (gill net, trawl, hook and line, etc.), a modification of the mix of gears in a multi-gear fishery, or by a change in fishing practice such as shift in area or time period fished (possibly as a result of a regulation such as a closed area or season). The pattern is expressed as a series of values ranging from 0.0 to 1.0.

exploitation rate = the proportion of a population at the beginning of a given time period that is caught during that time period (usually on a yearly basis). A catch in a year of 10 fish out of a stock of 100 is a 10% exploitation rate. Also the ratio of fish caught to total mortality (= F/Z when fishing and natural mortality take place concurrently (Ricker, 1975)). Also called rate of exploitation. Abbreviated as E.

exploitation ratio = the ratio of fish caught to total mortality (F/Z).

exploited = fished; harvested and put to use.

exploratory fishing = attempts to discover new resources with proven gear, to assess stocks and environmental conditions.

exposed field or portion = that part of a scale not covered by another scale. Characterized by the ridges low or missing and the possible presence of chromatophores (never in other fields) and ctenii.

exserted = projecting; extending beyond the general level, e.g. the lower pectoral rays of Triglidae which extend beyond the fin membrane.

extant = currently alive as applied to a taxon or of a specimen meaning still in existence. Opposite of extinct in the former case.

extended family = the family condition in Cichlidae where the parents as well as the offspring of previous spawning care for the young. Found in cavity brooders such as Julidochromis and Neolamprologus.

extended loan = a specimen or specimens loaned to a museum or scientist for a long period of time, sometimes indefinitely.

extended river = the lower reach of a coastal river that has been lengthened seaward by lowering sea level.

extender = a chemical solution used to dilute fish sperm for use in artificial fertilisation or cryo-preservation.

extensive culture = aquaculture in ponds by subsistence workers where low densities of fish are kept with minimum control, supplementary feeding, cost and profit.

extension = lengthening of the embryonic axis during the gastrula and early segmentation periods.

extension blood knot = a knot use for tying a dropper line, q.v., to a leader when two or more flies are used at one time. Various websites have animated steps showing how to tie this knot.

extension piece = tapered sections of netting between the belly and the batings and the cod end of a trawl. Also called pipe, swallow piece, tail, tail piece, taper, Y-piece.

extensive pond culture = extensive culture.

extent of occurrence = the area contained within the shortest continuous imaginary boundary which can be drawn to encompass all the known, inferred or projected sites of present occurrence of a taxon, excluding cases of vagrancy. This measure may exclude discontinuities or disjunctions within the overall distributions of taxa, e.g. large areas of obviously unsuitable habitat.

exterilium = a detached and trailing gut with many cirri and the anal opening on the dorsal edge found in larvae of some species, possibly of Brotulidae (Fraser and Smith, 1974).

exterior = outer.

external brooder = an ecological group comprising a series of reproductive guilds (q.v.) where the eggs are transferred to some structure on the fish for incubation. Structures vary from the mouth and gill cavity to specialised marsupia.

external gill = a gill extending beyond the gill slit or operculum, often found in larvae. e.g. embryos of some viviparous Elasmobranchii, the larvae of Gymnarchus, Polypterus and Protopterus.

external yolk syncytial layer = portion of the yolk syncytial layer outside the blastoderm margin during epiboly.

extinct = 1) no longer living as applied to a taxon. Opposite of extant.

extinct = 2) in the IUCN Criteria for threatened species, a taxon is Extinct when there is no reasonable doubt that the last individual has died. Abbreviated as EX.

extinct in the wild = in the IUCN Criteria for threatened species, a taxon is Extinct in the Wild when it is known only to survive in cultivation, in captivity or as a naturalised population (or populations) well outside the past range. A taxon is presumed extinct in the wild when exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual), throughout its historic range have failed to record an individual. Surveys should be over a time frame appropriate to the taxon's life cycle and life form. Abbreviated as EW.

extinction = death of all members of a clade or taxon.

extinction coefficient = a coefficient measuring the rate of extinction, or diminution, with distance of transmitted light in sea water.

extirpated = no longer living in an area under consideration, e.g. nationally; locally extinct.

Extra E = the highest grade of freshness in the European community.

extra- (prefix) = outside, beyond.

extra large = a grade of dried and salted cod (Newfoundland).

extra small = a grade of dried and salted cod (Newfoundland).

extrabranchial chamber = space between the operculum and the gills.

extractive use = removal from a resource, such as fish by fishing.

extralimital = beyond the limits (of a regional study or an identification key).

extramedullary haematopoiesis = in fishes, formation of blood outside the haematopoietic tissue in the kidney.

extrascapula (plural extrascapulae) = small bones bordering the posterior margin of the skull roof in primitive Teleostomi. They apparently originate from enlarged scales. One of a series of from 2-8 bones known variously as cervicals, extrascapulars, nuchalia, postparietals, scale bones, supratemporals or tabulars.

extrascapulae = plural of extrascapula.

extreme fluctuations = extreme fluctuations occur in a number of taxa where population size or distribution area varies widely, rapidly and frequently, typically with a variation greater than one order of magnitude, i.e. a tenfold increase or decrease.

extreme high water = the highest elevation reached by the sea as recorded by a water level gauge during a given period.

extreme low water = the lowest elevation reached by the sea as recorded by a water level gauge during a given period.

extrinsic gas bladder muscles = muscles with one end inserting on the gas bladder and the other end inserting elsewhere, as opposed to intrinsic.

extrinsic eye muscles = muscles attached to the eyeball and orbital wall for eye movement. The same in jawed and jawless fishes except the superior obliques which attach posteriorly in the orbit in the jawless fishes instead of anteriorly.

extrinsic sonic muscles = usually a pair, two pairs or more rarely three pairs of muscles inserted on the gas bladder and a neighbouring structure such as a bone (ribs, parapophyses), perhaps via ligaments. Insertions vary with the species and family. The muscles produce sounds by contracting the gas bladder. See also intrinsic sonic muscles.

extruded feed = food that has been extruded from a machine having been heated to 120°C under high pressure. The resulting pellets float, have better digestibility of starch but may be poor in vitamins. See also expanded feed.

extrusion = the process of pushing out eggs by a spawning female.

eye = 1) the point of attachment for the line on a hook or anchor.

eye = 2) opening at the inner end of the funnel in fish traps and pots.

eye = 3) a reference to markings on a fish body, often incorporated in the fish name.

eye = 4) as fish eye, variously an eye like that of a fish, a wide-angle lens on a camera covering about 180°, a weld defect having a hole or piece of matter surrounded by a circular area of brightness, a diamond or other gem cut too thin for proper brilliance, a small blemish in finished paper caused by a crushed and glazed particle, a cold or suspicious stare, blank, expressionless, ocular lymphomatosis in fowl, in oil drilling fluids, slang for a globule of partly hydrated polymer formed by poor dispersion during mixing. About 0.2-0.5 inches in size, they consist of a granule of unhydrated polymer covered by hydrated polymer and so are impervious to water and do not disperse.

eye = backstrop norman (a special u-shaped bolt to which the backstrop is attached).

eye diameter = the greatest distance in a straight line across the cornea between the borders of the cartilaginous eye-ball. Often misapplied to orbit diameter, q.v.

eye fluke disease = a disease caused by the metacercaria of strigeid trematodes (Diplostomum). The life cycle involves a snail, fish and the final host, a bird. Larval flukes invade the fish through the gills and reach the eye capillaries through the blood stream. Blindness can result. Symptoms include cloudy eyes and popeyes but these also have other causes. Small white cataracts may develop. Wild snails should be avoided in the aquarium. Also called diplostomiasis.

eye notch = in sharks, a sharp anterior or posterior indentation in the eyelid, dividing the upper and lower eyelids.

eye protrusion = exophthalmia, popeye.

eye spot = see eye-spot.

eye stalk = a movable peduncle bearing the eye of varying length.

eye stripe = a stripe of pigment passing through the eye region on the head of a fish, a form of disruptive colouration, q.v.

eye worm disease = eye fluke disease.

eye-fork length = straight or curved-body length between the posterior orbit and the fork of the tail; used in measuring billfish species. Abbreviated as EFL.

eye-spot = 1) a photosensitive structure in the anterior ventral surface of the brain in Amphioxi; contains primitive homologues of rods and cones and is probably able to detect differences in quantity of light but incapable of forming an image.

eye-spot = 2) any spot resembling an eye, often functioning to distract or confuse predators. Also called an ocellus.

eyed = eggs at a development stage of 38 days, e.g. in chinook salmon at 45°F (stages are green at 0 days, eyed at 38 days, sack fry at 69 days, swim up at 92 days and button up at 115 days).

eyed egg = a fish egg containing an embryo that has developed enough so that the black spot of the eyes are visible through the egg membrane. Indicates that the egg is less sensitive to movement and can be handled safely, e.g. for transportation.

eyed embryo = eyed egg.

eyed hook = the usual form of hook with a round hole at the end opposite the point for tying on the line.

eyed side = the side in flatfishes bearing both eyes, the uppermost side when resting on the bottom, opposite to the blind side. Also called upper surface but not dorsal surface as it is a flank.

eyelet = the rings or guides on a fishing rod through which the line passes.

eyemouth cure = brined and lightly smoked haddock headed and split so the bone is on the right hand side.

eyestalk = a moveable, elongate peduncle bearing an eye at the tip, e.g. in the larvae of Idiacanthidae. Placodermi and Chondrichthyes have an eyestalk, a small cartilage linking the eyeball to the braincase.

© Brian W. Coad (www.briancoad.com)

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