Deepwater Sculpin, Myoxocephalus thompsoni

Deepwater sculpin, Myoxocephalus thompsoni.

Separating the deepwater sculpin from other freshwater sculpin species involves an inspection of gill morphology and counts of head spines and fin rays. For example, this species is closely related to the fourhorn sculpin, but can be distinguished by its separated dorsal fin and by its lack of club-shaped head spines. In adult males, the second dorsal fin is enlarged and bears small tubercles. Otherwise, this species has a typical sculpin body with a large head and eyes, fan-like pectoral fins, and a rounded caudal fin. Its basic body colour is grey-brown on the sides and white on the belly. Four to seven "saddles" of darker colour are present on the back, while the rest of the body is spotted. Most fins have pale colour bars on them, but the pelvic fins are white.

The deepwater sculpin has a wide distribution throughout the North, inhabiting the lakes of southwestern Quebec, northwestern Ontario, the Great Lakes, Manitoba, Saskatchewan, and Great Bear and Great Slave Lakes. As well, it occurs on Victoria Island in the Arctic. It prefers depths ranging from 4 m to 366 m and is quite common in deep lakes, hence its name.

This species is considered a relict of the last Ice Age and was once found in Arctic marine or brackish waters, but was forced to retreat southwards as the ice advanced. When the ice melted, this species remained behind and as the saline lakes were slowly replaced by fresh water, the deepwater sculpin adapted to the changes in its environment. It was originally thought that this species was a subspecies of the fourhorn sculpin, but fossil evidence has shown that the deepwater sculpin is far older than its relative.

The deepwater sculpin eats crustaceans, larval chironomids, and fish eggs. In turn, they are preyed on by lake trout and burbot. Spawning takes place year-round, but peaks in August and early September. Females carry up to 1190 orange eggs, which are 2.1 mm in diameter, but little else is known about its mating behaviour. Its lifespan is 7 years, with females maturing at 3 years and males at 2 years.