Possible case of aggressive mimicry in a neotropical scale-eating fish

Abstract

Probolodus heterostomus, one of the scale-eating characoid fishes, is found in the coastal rivers of southeastern Brazil from Espírito Santo to São Paulo^1–3. The species is usually placed in the subfamily Cheirodontinae^2–4 although a taxonomic affinity with the Tetragonopterinae has been suggested¹. The latter view was apparently based largely on the morphological similarity of Probolodus with some species of Astyanax and especially A. fasciatus, a member of the Tetragonopterinae. The external similarity between the two species, which are sympatric over the Rio Paraíba drainage, is indeed striking (Fig. 1). But data accumulated from population samples, stomach contents and the behaviour of individuals maintained in aquaria suggest that Astyanax is the principal prey of Probolodus, at least in certain areas of its range. I suggest here that the similarity between these two genera is a form of aggressive mimicry^5,6 irrespective of taxonomic affinities.