Effect of food abundance on aggressiveness and territory size of juvenile rainbow trout, Oncorhynchus mykiss

► We examined the effect of food abundance on aggressiveness and territory size in rainbow trout, Oncorhynchus mykiss. ► Frequency of territorial aggression was highest at intermediate levels of food abundance. ► Territory size decreased by only 30% over a 32-fold increase in food abundance. ► Territory size was relatively insensitive to changes in food abundance. ► Territoriality may have a regulatory effect on population density.