The lake trout (Cristivomer namaycush) is the principal fish of Great Bear lake. The largest populations were found in semi-isolated bays, with smaller populations in the open lake on one hand and in river mouths and marshy areas on the other. The trout grow very slowly; by three years they are just over three inches (7.6 cm.) long and weigh one ounce (28 g.). A weight of one pound (0.45 kg.) is achieved in their ninth year and two pounds in their fourteenth year. Maturity is reached in from 13 to 17 years; the rate of growth in weight increases after maturity. Mature fish appear to spawn only every second or third year. Spawning begins about the middle of August. The young trout spend their first four summers in shallow water near shore. The adults feed on all food sources in the lake,—plankton, bottom organisms, fish and terrestrial insects. Fish preparing to spawn have pale flesh; others have orange to red flesh. There is some evidence of two morphologically distinct groups, probably resulting from environmental differences. A list of the parasites of the trout is given. A detailed analysis of the incidence of cysts ofTriaenophorus crassusindicates that adult trout remain in one locality throughout life.