Sculpins are most abundant in clear, rapidly flowing freshwater streams, and are usually found in association with trout, dace, and other fish requiring clean water and low temperatures. Sculpins are bottom-dwellers, and seldom swim more than a few centimeters above the substrate. They are most commonly found resting beneath flat rocks. They are carnivorous, and prey primarily on insect larvae, crustaceans, and fishes. Field studies show that small sculpins prefer mayfly nymphs and small worms.
Larger individuals tend to eat caddisflies, crayfish, larger worms, etc.
Smaller sculpins are quite commonly eaten by larger individuals in this highly cannibalistic species. Eggs are also cannibalized during the breeding season. Mottled sculpins breed in early spring. The breeding season begins when adult males occupy cavities beneath rocks on the streambed. Males darken considerably so that their heads become jet black and their dorsal fins become outlined in reddish-orange.