AGGRESSIVE BEHAVIOR OF UNDERYEARLING KAMLOOPS TROUT

Abstract

The aggressive behavior of juvenile Kamloops trout (Salmo gairdneri kamloops Jordan) consists of chasing, nipping, retreating, threatening, and fighting. These different components are described. Territorial defence appears to be the end result of this behavior. Aggressiveness disappears at low light intensity when the fish settle to the bottom and remain quiet. A seasonal decline in aggressive behavior seems to occur during the spring. The sign stimulus releasing attack is a moving fish-shaped object approximately the same size as the trout. Dark colors have a stronger releasing value than bright colors. Fins and color patterns do not seem to be involved in the sign stimulus.