Competitor density and aggressive behavior influences the ability of fish to use food resources during
aquaculture production. Using cutthroat trout Oncorhynchus clarkii (Richardson) from the same filial generation, this
study investigated the effects of both body size and rearing density on aggression and feeding behavior. Four experiments
were conducted using different numbers of both small and large trout obtained after grading. In each experiment,
regardless of the number of each size of fish, small fish made significantly fewer attempts to forage in comparison to large
fish. However, the number of aggressive interactions increased as small fish densities increased. These results suggest that
grading and rearing differently-sized fish separately during rearing will likely maximize growth and rearing efficiencies in
wild-strain cutthroat trout during hatchery rearing.