The Peace/Williston Fish and Wildlife Compensation Program (PWFWCP)

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Slimy Sculpin
Cottus cognatus

What do they look like?

A slim-bodied sculpin with two chin pores and, in profile, a blunt snout. The lateral line is incomplete, and the dorsal fins are usually separate. The anal fin has 10-13 rays with the anterior rays deeply incised. The anal fin base is shorter than the head and there are no palatine teeth. The entire body is black in breeding males except for an orange trim on the first dorsal fin. Breeding females retain their normal colour but also have a pale orange trim to the first dorsal fin. When gravid they have noticeably swollen abdomens.

Where do they live?

In Northern B.C., slimy sculpins occur in lakes, ponds, small streams and large rivers. In lakes, the adults are usually associated with coarse gravel or cobble substrates. Most collections from lakes in Northern B.C. are from littoral regions; however, in Lake Superior slimy sculpins occur down to 100 m. It is not known if they reach similar depths in B.C. lakes.

In flowing water, northern slimy sculpins are found from small headwater streams to large lowland rivers. In B.C., they are often the only non-salmonid in third-order streams and in these situations they are usually collected in quiet water over sand and silt bottoms. Apparently, slimy sculpins are not sensitive to turbidity: they occur in waters ranging in clarity from gin-clear to tannic in colour.

Slimy sculpins have a preferred temperature of about 10 °C. Most southwestern populations are found in cold, headwater streams or in glacier-fed rivers. In these environments, in the summer, adults are associated with coarse gravel or cobbles in shallow riffles, while the young-of-the-year are found along stream edges in quiet water (often in flooded vegetation or adjacent to overhead cover). Juvenile slimy sculpin occupy habitats similar to those used by adults; however, they are found closer to shore and in shallower water than adults. Newly hatched young-of-the-year are associated with shallow water and flooded vegetation.

What is their life like?

There is no published account of the life history of the slimy sculpin in British Columbia. Slimy sculpins generally spawn in the spring when water temperatures rise above 4 °C. In B.C., spawning dates range from mid-March to early-April in the south to mid-May in the north. Like most sculpins, males nest under rocks and are territorial. Females deposit their sticky eggs on the underside of the nest-rock. Here, they are fertilized by the male. The male guards the eggs until they hatch. The eggs range in colour from light yellow to amber-red. In B.C., egg numbers range from about 60 to 650. Normally, water temperatures increase during the incubation period (from about 4 °C to 8 °C) and, under these conditions, the eggs take about a month to hatch. The newly hatched larvae are roughly 7 mm long and have a large yolk sac. Young-of-the-year range from 30-32 mm in length by the end of their first summer. So far, the oldest slimy sculpin aged in British Columbia was in its eighth growing season (7+).

What do they eat?

Young-of-the-year slimy sculpins forage primarily on chironomid larvae but, as they grow, the nymphs and larvae of larger aquatic insects are added to the diet. Although adults and juveniles include mayfly and stonefly nymphs, and caddis larvae in their diet, Chironomid larvae are still a major food. Large adults also eat appreciable quantities of aquatic beetles, snails, and amphipods.

What is their distribution? Cottus cognatus is the only North American sculpin that also occurs in Siberia. In North America, slimy sculpins range from Alaska, British Columbia, northern Washington, and northern Idaho in the west across the northern Great Plains east as far as Labrador. In B.C., slimy sculpins occur in cold waters throughout most of the province. Although slimy sculpins are widely distributed in B.C., they are clearly an interior species and only approach the coast in a few northern rivers (e.g., Alsek, Taku and Stikine systems). In the Williston-Dinosaur drainage basin C. cognatus is the most common and widely distributed sculpin.

View Peace Williston distribution map.