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INHIBITION OF CANNIBALISM IN CICHLA OCELLARIS AND HYPOTHESIS OF PREDATOR MIMICRY AMONG SOUTH AMERICAN FISHES

Cannibalism is a widespread phenomenon which occurs in both vertebrates and invertebrates (see Fox, 1975a, for a review). Historically, many investigators have tended to dismiss cannibalism among animals as unnatural behavior, such as an artifact of laboratory conditions, or of minor significance when observed in natural populations (e.g.: Kipling and Frost, 1970). Others have argued convincingly for its recognition as a natural and important mechanism of population regulation (Fox, 1975b), and recent experimental work has indicated that cannibalism does have a heritable genetic basic (Thibault, 1974). Freshwater organisms constitute the largest known group of cannibalistic animals (Fox, 1975a), and of these a great many are fishes. Cannibalism is widespread among viviparous (primarily tropical) fishes (Thibault, 1974; Aquarium Digest International, 1972), and has also been reported for numerous common temperate zone species including: perch (Perca flavescens, Clady, 1974; P. fluviatilis, McCormack, 1970), yellow bass (Roccus mississippiensis, Bulkley, 1970), smallmouth and largemouth bass (Micropterus dolomieu and M. salmoides, Clady, 1974), pike (Esox lucius, Frost, 1954; Kipling and Frost, 1970), and walleye (Stizostedion vitreum, Chevalier, 1973), to cite a few examples. Of these species Micropterus, Esox, and Stizostedion are all piscivorous. Cannibalism is also widely distributed among marine fishes including smelt (Osmerus eperlanus) and cod (Gadus morhua) (Nikolsky, 1963). Given that cannibalism may be a normal response to environmental factors (Fox, 1975a), and that it occurs commonly in freshwater fishes, especially predators, it seems curious to find a situation where it is absent in a freshwater predatory fish. This appears to be true, however, for a population of highly voracious predatory fish, the South American cichlid, Cichla ocellaris. In this paper I will present evidence supporting the absence of cannibalism in this species, experimental data which indicate the mechanisms maintaining this inhibition, and the evolutionary implications, including the hypothesis of a previously unrecognized form of mimicry among fishes of the lowland tropics of South America.