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”.