Goldfish immersed in a solution of thyroxine, testosterone, or stilboestrol are more active than untreated fish. The strength of electrical stimulus required to produce a standard response is also less in similarly treated goldfish. Coho and sockeye salmon yearlings tested with the same hormones and sockeye salmon yearlings treated with dienoestrol or nylestin show a decrease in time required to make a standard response in flowing water. These data are discussed in relation to the appetitive behavior of migrating fishes.