Species Accounts
Percopsidae - Trout-perches - Omiscos
The Trout-perch Family contains only 2 species in temperate North American freshwaters, 1 of which is found in Canada, the other, the Sand Roller, being restricted to the Columbia River drainage in the U.S.A.
The name derives from their anatomy, which contains characters of both the trout or salmon-like fishes and the perch-like fishes. They include an adipose fin, weakly ctenoid scales, a scaleless head, weak spines at the origins of the dorsal, anal and pelvic fins, and 7-8 pelvic soft rays. Biology is summarised in the species account.
Trout-perch / Omisco
Percopsis omiscomaycus (Walbaum, 1792)
Taxonomy
Other common names include Silver Chub and Sand Roller.
Key Characters
The combination of weakly ctenoid scales, an adipose fin, weak spines in the dorsal, anal and pelvic fins, and the pelvic fin base under the pectoral fin is unique.
Description
Pyloric caeca number 7-14, arranged in 2 rows on each side of the intestine. Dorsal fin with 2 weak spines, 9-12 soft rays. Anal fin with 1 weak spine and 5-8 soft rays. Pelvic fin with 1 weak spine and 7-9 soft rays. Pectoral fin rays 12-15. Scales 41-60 in a complete lateral line. Gill rakers are short with small teeth and number 9-12.
Colour
Background colour is silvery with 5 rows of black spots. There are 9-12 spots on the back mid-line, 7-12 weak spots on the upper flank and 8-13 obvious spots or blotches along the mid-flank. The back may have a purplish tinge or be yellowish, brownish or greyish. Fins are mostly clear with some faint pigment along fin rays. Large cavities on the cheek and lower jaw are silvery-white. The body is often translucent and the silvery-white internal body cavity lining can be seen through the skin.
Size
Reaches 20 cm.
Distribution
Found in central and northern North America. In Canada it occurs from western Québec, including around James Bay, throughout Ontario, Manitoba and Alberta, but only in northeastern British Columbia, and in the eastern Yukon, Nunavut and the Northwest Territories.
Origin
This species entered the NCR from a Mississippian refugium (Dadswell, 1972) or possibly a Beringian refugium (Mandrak and Crossman, 1992).
Habitat
Trout-perch favour deeper water of lakes (down to 60 m) but enter streams to spawn in the east. In the NCR it has been caught in streams with slow to medium currents, mud, debris or rock bottoms and light brown water. Their preferred temperature is 15-16°C and they are tolerant of turbidity.
Age and Growth
Males live to 3, and occasionally to 4, years in Lake Champlain with females living to 6 years. Maximum age elsewhere is reported as 8 years but maturity can be reached as early as 1 year. Females are larger than males.
Food
Food includes aquatic insects, crustaceans and small fish such as darters and minnows, perhaps taken mostly at night during an inshore migration. Trout-perch are an important food for Northern Pike, Walleye, Burbot, Lake Trout, Brook Trout, Sauger, Yellow Perch and Freshwater Drum. Often the only evidence of Trout-perch in predator stomachs is the pyloric caeca, which produce, and are therefore resistant to, digestive enzymes.
Reproduction
Spawning occurs in streams or over sand and gravel in lake shallows. Most southern Canadian populations are believed to migrate to spawn in streams in May and then return to lakes. Lake spawning may run from May to August. In the north, ripe males and females have been caught in June and July. Egg diameters are up to 1.85 mm and egg numbers to 1825. Eggs are heavier than water and stick to the bottom.
Importance
Occasionally used as bait but otherwise not of direct, commercial importance. One important function of this species may be as a nutrient transporter. Lake Trout are confined to cool depths of lakes and cannot feed in the food-rich but warm shallows. However Trout-perch feed in the shallows at night and return to deep water for the day where they fall prey to the Lake Trout.
© Brian W. Coad (www.briancoad.com)