Agonistic behavior and social dominance relationships between similar-sized, wild, adult brook trout (Salvelinus fontinalis) and rainbow trout (Salmo gairdneri) were examined in a laboratory stream. Frequency of movements, aggressive encounters, and consumption of food items by trout when held as single specimens, intraspecific pairs, and interspecific pairs were compared. Rainbow trout were more mobile, aggressive, and successful foragers on drifting prey than brook trout; however, neither species appeared to possess a competitive advantage in establishing social dominance or displacing interspecific rivals. Brook trout were dominant in 9 of 14 interspecific matches. Female trout were dominant in 6 of 10 opposite-sex matches. Dominant trout, regardless of species or sex, exhibited significantly greater mobility, aggressiveness, and feeding success than subordinate trout.