is the Latin troct-a, from the Greek troktes, the greedy fish (trogo, to eat). The trout is very voracious, and will devour any kind of animal food.
“[Roland] was ... engaged in a keen and animated discussion about
Lochleven trout and sea trout, and river trout, and bull trout, and
char which never rise to the fly, and par which some suppose [to be]
infant sahnon, and herlings which frequent the Nith, and vendisses
which are only found in the castle loch of Lochmaben.” —
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894