Trout-perch of Heming Lake attain III years of age and 90 mm. in fork length. In May they ascend small tributaries to spawn on silt and boulder bottoms, at a temperature of 40°–50°F. Average egg content was 349, with range 210–728 in 11 fish. Trout-perch taken in the lake were infested with 0 to 6 cysts each (av. 1.4) containing procercoids of the cestodeTriaenophorus stizostedionis. Most cysts were in the liver or gonads, very few in the muscle. Trout-perch were eaten in large numbers by pike,Esox lucius, and much less frequently by walleye,Stizostedion vitreum. Only the latter contained adultTriaenophorous stizostedionis.