The common names of fishes vary with language between countries and within a country with local usage. This problem is overcome to the scientists' satisfaction by the scientific name, consisting of two words, the genus name and the specific or trivial name. A genus, e.g. Barbus, may contain many species but each species is a unique combination of Barbus and a specific or trivial name. This scientific name is used the world over whatever the local common name may be. It is always written in Latin script and the genus and trivial names are derived from and spelt according to rules of grammar in Latin and Classical Greek. Both these languages are "dead" so the rules and spelling are fixed and not subject to change with time as modern languages are. It is generally felt that the advantages of this system outweigh the unfamiliarity of Latin and Greek words and grammar for most people.

As an example of the scientific name, we can consider the first species dealt with in this work, the Caspian lamprey or Volga lamprey Caspiomyzon wagneri (Kessler, 1870). The scientific name is underlined or set in italics or bold face to denote its scientific status. Caspiomyzon is the genus name and wagneri the trivial or specific name. This species was first described by Kessler in a publication dated 1870. Kessler placed this new species in the genus Petromyzon but L. S. Berg later published reasons for placing it in a distinct genus, Caspiomyzon. The parentheses around the author (or first describer of the new species) and the date of description indicate that its generic allocation has been changed.

The scientific name is also used to show relationships between species and it can therefore be changed if views on the relationships of the species are changed according to the "International Code of Zoological Nomenclature". The Fourth Edition of the Code came into effect on 1 January 2000. Errors also arise in giving species scientific names and these must be corrected by name changes according to the Code. The Code is complicated and detailed explanations based on fishes may be found in Eschmeyer (1998; this Catalog of Fishes is now online, see Links). Some of the more common reasons for name changes are given below.

A single species may be described twice, either by the same person or by two people. At the time of these descriptions it was genuinely believed that there were two species but subsequent studies showed that they were the same. This error often arises with confusion between juveniles and adults and between males and females which may be quite different in appearance. Older collections from remote areas often comprised only a few specimens and could be in rather poor condition by the time they came into the hands of an ichthyologist and were described scientifically. An example of confusion of males and females of the same species is found in the genus Aphanius. In 1910, J. T. Jenkins described three species of Aphanius (under the genus Cyprinodon as it was recognised then) from near Shiraz. This material had been collected in 1872 by W. T. Blanford and was comprised of 10 specimens, mostly in good condition. The three species were Cyprinodon blanfordi, C. persicus and C. pluristriatus. The first of these was thought by Berg (1949) to be a female Aphanius sophiae and the latter two to be males differing in characters not now considered to be specifically important. I have a differing opinion! It is also possible, where two people are concerned, that the author who published his description later was ignorant of the first author's work. The first name published has priority and the second name is called a synonym and is no longer used. There may be several synonyms for a species. These are listed in the species descriptions. There is also the problem of misidentification of specimens. When these specimens are available for study identification can be confirmed (or amended) but often specimens are discarded or lost. These errors too may be listed in a synonymy. Krupp (1984a) gives a synonymy for Aphanius cypris which amply illustrates how a scientific name may be mis-applied (there are 89 uses of names which all refer to one species in Krupp's opinion). A. cypris is now thought to be correctly named A. mento.

Occasionally the same name is given to two distinct species because the later author was not aware that the name had already been used. The name of the species described first is called a senior homonym and is retained while the later species name, the junior homonym, must by replaced.

The genus name of a species can be changed because an ichthyologist, who has studied the species and its relatives in detail, considers that it is more closely related to another species or group of species with a distinct genus name. A similar case was discussed above with Caspiomyzon wagneri where a new genus was erected for this species. In both cases, parentheses are placed around the author's name and the date of description to indicate that the genus name used has been changed. The species placed in a different genus will retain its trivial or species name unless this trivial name is already in use in the different genus. Homonymy has then occurred and the species which has priority retains its trivial name and a replacement name must be given to the more recently described species. It is not unusual for scientists to disagree about the interpretation of the same data and a species may have a long and complex career being switched from genus to genus as publications advocate one view or another of its relationships.

There is a higher classification which groups together related genera into Families, Families into Orders and Orders into Classes. The vast majority of Iranian freshwater fishes belong to the Class Actinopterygii, the ray-finned bony fishes, with only the Caspian lamprey in the Class Cephalaspidomorphi. Some sharks penetrate freshwater and these belong to a third Class, Chondrichthyes or cartilaginous fishes.

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© Brian W. Coad (www.briancoad.com)