FIN-NIPPING PIRANHAS

Prey selection by South American fin-nipping piranhas was investigated in the field and in laboratory prey-choice experiments. Our comparati ve data from laboratory assemblage experiments indicate that different piranha species select prey species in different proportions, and tha t the differences are associated with the body form and swimming behav ior of predator and prey. In the field, cichlid fishes were the most p referred prey for fin-nipping piranhas. We tested the hypothesis that some South American cichlid fishes suffer lower levels of fin predatio n because of their caudal (tail) mimicry of the head region. Most of t he large cichlids that inhabit lowland aquatic habitats with piranhas have densely scaled median fins and bright caudal ocelli (eyespots) at the base of the tail that mimic the size and vertical position of the true eye.