Montana Field Guide

The mottled sculpin is well-named from the way it blends in with the rocks. The mottled sculpin is a native fish, widespread in Montana in mountain streams east of the Continental Divide. Like all sculpins, the mottled species eats primarily aquatic insects. They occasionally eat small fish or trout eggs but this is not a large part of their diet.

The back and sides are slate to brown with mottling and dark blotches. They may have two or three dark saddles under the second dorsal fin. The underside is whitish. The first dorsal fin is fringed with orange or red on breeding males. Palatine teeth are present.

They prefer riffle areas of fast-flowing streams that are clear and have rocky bottoms.

Food includes a variety of immature aquatic organisms, but midge and acddis larvae are by far the most important. A study in southwest Montana showed bottom-dwelling aquatic insects comprising 99.7% of the diet.

The species serves as a forage fish for predators, often trout.

They are sexually mature in 2 years. Spawning occurs in May-June. The eggs hatch in 20-30 days at 50-60 degrees F. A southwest Montana study showed spawning throughout the month of June.