Most members of the Sculpin family are Northern Hemisphere saltwater fishes, but some species have adapted to living in fresh water. Most freshwater Sculpins are small bottom-dwellers that prefer cool, headwater streams. In Pennsylvania there are three common Sculpin species for sure: The Mottled Sculpin (Cottus bairdii), the Blue Ridge Sculpin (Cottus caeruleomentum), the Slimy Sculpin (Cottus cognatus) and the Potomac Sculpin (Cottus girardi). The Spoonhead Sculpin (Cottus ricei) and Deepwater Sculpin (Myoxocephalus thompsoni) live in the depths of the Great Lakes and might be present in Lake Erie. They are extirpated species in Pennsylvania.
The Mottled Sculpin has a wide range over the central United States and Canada. It is common in clear, clean upland and mountain streams. Mottled Sculpins often live in company with Brook and Brown Trout, but they can also live in waters too warm for Trout. In Pennsylvania, the Mottled Sculpin is found in all of the state’s watersheds.
The Slimy Sculpin is found from New Brunswick, Canada, to Alaska. In Pennsylvania it lives in the Susquehanna and Delaware systems. It can thrive either in streams or lakes, but it must have a clean, stony bottom. Where the habitat is to its liking, it can become many times more abundant than the Trout in the same stream. This is typical of a prey species.
The Potomac Sculpin, as the name suggests, lives in the Potomac River watershed in Pennsylvania. It also lives in some nearby headwaters of the Susquehanna River. It is found in the rocky riffles of warm streams and the quiet pools above the riffles.
The Blue Ridge Sculpin is a newly discovered species. It was determined to be distinct from the Mottled Sculpin because of differences in body morphology and protein analyses. Additional information on this species’ abundance and distribution will become available as researchers begin to examine historic and future specimens more closely.
Sculpins are small, camouflaged fish reaching four or five inches in length. Their dark-and-light mottled color pattern helps them hide on the stream bottom. The broad head, fleshy mouth and upward-peering eyes look large for the rest of the body. Sculpins are compressed top to bottom, tapering quickly from a robust head to a narrow tail. The large, fanlike pectoral fins and the Sculpin’s flattened body shape allow it to stay pressed against the stream bottom, maintaining its position when in swift water–a hydrodynamic adaptation. Sculpins have no swim bladder, so they are nonbuoyant and move over the bottom in short spurts. There are two dorsal fins. The front fin is spiny and the rear one is soft. Both are held erect. The pelvic fins have a single spine and soft rays. The Sculpin’s body is scaleless, except for some scattered areas that have small, sharp scales called “prickles.” The tail is straight or rounded.
The Mottled Sculpin is light to dark-brown with darker mottling on its back and sides, and a belly that is pale-brown or whitish. Its chin has irregular dark pigment, and there are spots and streaks of darker color on the dorsal, caudal, pectoral and anal fins. Mottled Sculpins also have a short patch of teeth on each of the paired bones (palatine) in the forward roof of the mouth.
Slimy Sculpins are dark-brown with darker mottling. They are lighter on the sides, blending to whitish on the belly. The spiny dorsal fin is dark at the base, and clear along its top edge. The second dorsal fin, caudal fin and anal fin may have light bars, and the pectoral fins are widely barred. There is no mottling on the chin, and no teeth on the palatine bones. The Mottled Sculpin and the Slimy Sculpin are difficult to tell apart in the field.
Mottled Sculpins spawn in early spring. The males choose a hollow beneath a rock in a stream riffle. They invite females to spawn there by enacting an elaborate courtship ritual. The male moves his head quickly, bites the female, and may even grab her head and pull her toward the nest cavity. The eggs are laid on the underside of the rock, in a sticky mass. They hatch in two or three weeks. The male guards the nest as the eggs develop. Slimy and Potomac Sculpins spawn similarly.