Caudal Eyespots as Deterrents against Fin Predation in the Neoptropical Cichlid Astronotus ocellatus

Abstract

Astronotus ocellatus and several other large cichlid fishes of South America exhibit bright ocelli, or eyespots, near the base of the caudal fin. Astronotus ocellatus sympatric with fin-nipping piranhas of the genus Serrasalmus shows less extensive fin damage that sympatric cichlids of similar size that lack distinct caudal ocelli. Ecological data and observed interspecific behavioral differences support the hypothesis that eyespots reduce piranha attacks by confounding visual recognition of the prey's caudal region. Dense scalation of the unpaired medial fins, especially the caudal fin, masks visual cues for fin recognition, further enhancing head mimicry by the caudal region. The hypothesis that caudal ocelli in A. ocellatus, and perhaps other large cichlid fishes, function primarily as eye mimics for defense against fin predators is more parsimonious than Zaret's earlier inhibition of cannibalism hypothesis.