Effect of Diets Supplemented with Live Food on the Foraging Behavior of Cultured Fall Chinook Salmon

The use of diets supplemented with live food to increase the postrelease foraging ability of hatchery‐reared fall chinook salmon Oncorhvnchus tshawytscha was investigated. Replicate groups of fry were reared in six 2.4‐m‐diameter circular tanks and fed one of two diets. Fish in three tanks received a commercially available pelletized diet; fish in the other three tanks were given the opportunity to forage on natural live prey (mysids, mosquito larvae, chironomid larvae, and daphnia) prior to their daily ration of pellets. Foraging by individual fish was observed in special 200‐L tanks, and fish conditioned to live food fed on twice as many familiar prey (chironomids) and novel prey (mayfly larvae) as unconditioned fish fed on. This suggests that diets supplemented with live food can be used to increase the postrelease foraging effectiveness of hatchery‐reared chinook salmon.