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2 METHODS Colorado squawfish used in the experiment were hatched and reared at the Willow Beach National Fish Hatchery in 1974. They were held in covered outdoor concrete raceways and fed trout pellets and small rainbow trout (Salmo gairdneri) until they were transferred to Utah Division of Wildlife Resources Fisheries Experiment Station, Logan, Utah, in 1980. At the sta- tion, fish were held in outdoor concrete ponds (10 m x 20 m and 0.75 m deep) and fed trout pellets and small rainbow trout for approximately six months. In the fall of 1980, 60 Colorado squawfish were transferred to the Utah Water Research Laboratory, Logan, and held in covered 800-liter circular flow- through aquaria. The water was dechlorinated Logan City water heated to 15 ± 1 C. The photoperiod was 14h light and 10h dark. Fish were fed pelleted commercial trout feed or rainbow trout on alternating days. At the time of the study fish ranged in size from 360-512 mm TL (x = 444 mm, SD = 29 mm). Channel catfish used in this experiment were hatched and reared at a commercial hatchery in southern Idaho in June 1982. They were held in con- crete outdoor raceways and fed a special catfish blend of food until trans- ferred to the laboratory in August 1982 where they were held in 100-liter flow-through aquaria. The water source, temperature, and photoperiod were the same as for the Colorado squawfish. The catfish were fed commercial trout pellets (#3 crumbles) twice daily. They ranged in size from 51-125 mm TL (x = 77, SD = 10.5, n = 600) when used in tests. Several preliminary experiments were performed (Appendix A) before a final protocol was established. The aquarium where feeding trials took place was a covered flow-through circular tank 1.5 m in diameter with a water depth of 30.5 cm. Water temperature and photoperiod were the same as