Updated: Mar 15, 2021
If you've ever fished rivers where trout and whitefish coexist, you know the deflation of realizing that the fish on the end of your line isn't the massive trout you hoped. Instead, you pull in whitey after whitey and quickly begin to disdain these under-appreciated fish. But you shouldn't blame these fish for doing what they do best: sucking up nymphs that are bouncing deep off the bottom of a stream.
Whitefish have sub-terminal mouths, meaning their mouths are oriented toward the river bottom. Other sub-terminal species include suckers and carp. The mouth orientation of these fish offer clues to anglers about how they prefer to feed. Whitefish, suckers, and carp, with their downward facing mouths, tend to eat food off the bottom of their environment. On the other hand, trout have terminal mouths, meaning their mouths open straight down their snout, and favor neither upturned nor downturned feeding. Trout are therefore more versatile feeders.
Pretty easy right? Now we can strategize our angling tactics accordingly.