Optimality models designed to explain the occurrence of feeding territoriality predict that the frequency or intensity of aggression will peak at intermediate levels of food abundance. To test whether this prediction applies to the competition for ephemeral patches of food, we manipulated food abundance over a broad range of values in two separate experiments (24- and 64-fold, respectively) while monitoring the aggressive behaviour of juvenile convict cichlids,Archocentrus nigrofasciatum , competing for the food. In both experiments, the rate of aggression was low when food was scarce, increased as food abundance increased, and decreased when food was provided in excess. This dome-shaped pattern of aggression was caused partly by higher encounter rates between fish and partly by a higher proportion of encounters resulting in aggression, when food was at intermediate levels of abundance. Our results suggest that convict cichlids display behavioural flexibility: in response to changes in food abundance, they appear to change both their likelihood of using aggression when encountering a conspecific and their willingness to enter an occupied patch.