The National Trout Center uses FishBase, a global compendium of biodiversity information on more than 32,000 species of fish, for authoritative information on the taxonomy, biology and ecology of species in the salmonid family, as well as other fishes that occur in environments inhabited by salmonids.
The naming of fishes and all other organisms known as animals is governed by the International Code of Zoological Nomenclature. This code specifies how names are established and which name must be used (in scientific discourse) in case of name conflicts. The Code determines what names are valid for any taxon in the family, genus, and species groups.
Taxonomy of the Salmonidae
The Latin name of the family is Salmonidae, with a “-dae” suffix denoting the “family” taxonomic level. The anglicized name is “salmonid”, refering to the salmon family within the larger taxonomic order, “Salmoniformes”. Included are three sub-families, Salmoninae, Coregoninae, and Thymallinae, bearing the sub-family suffix “-nae” and denoted with the vernacular names[link to: “Vernacular Names” file] salmon (and trout), whitefishes, and grayling. Sub-families are usually designations that collect together closely related species, a practice important in systematics and taxonomy, but only infrequently carried over into the jargon of the general public. Genus (plural “genera”), the next grouping of species below the sub-family level designates a taxonomic platform suitable for assigning Linnaean Latin binomial names to individual species.
The species designation is the fundamental unit of classification that has served the biological sciences since Swedish zoologist Carl Linnaeus published Systema Naturae in the middle of the 18th century. The structure of the name in print is genus, always capitalized, followed by the “specific epithet”, always lower case and never capitalized. The two-part name for a particular species is called its “binomial” and it is usually italicized (or underlined) in printed media. Each of the two parts of the name may carry additional meaning peculiar to the life history of the named animal. Thus, for the brook trout, Salvelinus fontinalis, the genus identifies the fish with the old name for char, based on the root of the German “saibling” meaning little salmon. The specific epithet, means living in springs.
FishBase recognizes 11 genera and 228 species world-wide in the family Salmonidae. All salmonids are native to the northern hemisphere, but widely planted in suitable habitat in the southern hemisphere. In the sub-family Salmoninae (trout and salmon) the best-known genera are Salmo, Oncorhynchus, Salvelinus, and Hucho. The Coregonines (whitefish) include the genera Coregonus, Prosopium and Stenodus, and the Thymallinae (graylings) are represented by two species in the genus Thymallus.
Trout are among those fishes that have remarkable ability to adapt their own body colors to their environments. Three common types of adaptation are readily apparent among salmonids. One is called “countershading” in which the dorsal surface (upper) of the fish becomes darker, or, colored the same as the water would appear to an observer looking downward toward the fish. As you might imagine, the ventral surface (lower) of the body can be colored light, or, white, so that an observer under the fish and looking up toward the water’s surface would see a light or white hue. In this way, countershading helps to make the fish less visible to potential predators, such as birds, or other fish. Small stream (upper) and large lake (lower) rainbow trout
Another color adaptation is for the fish to assume an overall darker or lighter coloration according to the color of the habitat it occupies. In the illustration to the right, both countershading and overall lightness/darkness color adjustments are illustrated by rainbow trout. In the upper panel, a trout from a southeastern Minnesota stream illustrates a darker dorsal surface comparable to the color of the gravel in the stream below it. The sides of the trout show the characteristic “rainbow” color stripe and overall dark speckles. Compare this image with the lower panel in which we see a rainbow trout caught from the clear, deeper waters of Lake Huron. Again, the dorsal surface is dark, but with a greenish hue as the water appears when looking down into the lake. The lateral surface of the trout is strongly reflective rather than deeply colored, and the ventral surface (belly) is stark white.
The ability to change the lateral surface of the fish to appear much like the surrounding habitat also helps the fish to avoid predation. In this image of a brown trout in our aquarium at the National Trout Center, you can see that the blotchy coloration on the side of the trout has some of the color characteristics of the gravel over which the fish is swimming. Color changes of this kind, from uniform to blotchy, or, from reflective to non-reflective, or, overall dark to light, may take place in a matter of minutes or hours, or, may be related to a life history stage or change in the fish’s behavior over the course of weeks or months.
There are many other examples of color adaptation among salmonids, other fishes, and other animals. Natural disguises include transparency that confers a kind of “invisibility” to the fish. This is most frequently seen in larval or juvenile fish. Note that the transparency of the right pectoral fin and the dorsal fin of the aquarium trout make the margins of the fins difficult to discern. The opposite of invisibility is overt mimicry (biologists call this Mullerian mimicry) whereby the fish adopts a distinctive and conspicuous coloration that mimics the colors of a dangerous or unpalatable species. This is uncommon in fishes, but very well illustrated by the coloration of the king snake (harmless species), and the coral snake (deadly poisonous). For an interesting discussion of coloration of fishes, including countershading.
Trout and closely related species such as salmon, whitefish and grayling have played venerable roles in the cultures of the northern hemisphere. They are manifest in our literature, music, commerce, gastronomy, mythology, economics, religions and politics. These varied roles have spawned a plethora of names for the various species.
The fishes themselves have engendered many of the names by which they are known. For example, the troutperch, Percopsis omiscomaycus, a small species of fish inhabiting a broad range of North American cool and cold-water lakes and streams, is neither a trout nor perch, nor a hybrid of these fish. They share an anatomical feature of true trout, a spineless, rayless, (fleshy) adipose fin between the dorsal fin and caudal (tail) fin. They are also similar in appearance to the common yellow perch.
Likewise, human interest in a particular species may have evoked a name associating a fondness for one fish in the naming of another. The sea trout of the Atlantic and Gulf coasts of North America, https://en.wikipedia.org/wiki/Cynoscion_nebulosus, actually a member of the drum family, and the greenling sea trout of the Pacific coast, Hexagrammos decagrammus, are not trout at all but are known in their respective geographic regions by vernacular names that include the word “trout”. To further complicate matters, “sea trout” can also refer to true trout or salmon that live in the sea or migrate to or from the sea.
Original use of the term “sea trout” by the Swedish zoologist Carl Linnaeus, referred to the anadromous form of the brown trout, Salmo trutta. In the 1758 edition of Systema Naturae, Linnaeus also described a lake-dwelling form, Salmo lacustris, and a river-dwelling form, Salmo fario. This behavioral and geographic disdinction has run rife through our naming of various fish allowing rainbow trout, for example, Oncorhynchus mykiss, to be denoted as steelhead, Kamloops, and red-band trout. Similarly, brown trout imported to North America have sometimes been referred to by their geographic origins, hence, “German brown trout”, or, “Loch Levan brown trout”.