Body shape variation of three species of Percichthys in relation to their coexistence in the Limay River basin, in northern Patagonia

We describe morphological variation within and among three species of Percichthys (Perciformes, Percichthyidae) inhabiting two reservoirs within a single river drainage (Limay River) in Argentina. Two small-mouthed 'percas', P. vinciguerrai and P. trucha were found in both reservoirs (Alicura and Piedra del Aguila), and a third species, the large-mouthed perca, P. colhuapiensis, was found in Piedra del Aguila. There was some specialization in diet where the three species coexisted. The large-mouthed perca ate a higher proportion of large prey (>25 mm) and a smaller proportion of small prey (<15 mm) than did the small-mouthed species, suggesting some diet specialization based on prey size. Percichthys trucha and P. vinciguerrai had smaller gapes, as indicated by shorter heads and jaws, and narrower mouths, in Piedra del Aguila where they coexisted with the large-mouthed species, than in Alicura where the competitor was virtually absent. Thus the direction of morphological changes in trophic-related characters in P. trucha and P. vinciguerrai is consistent with the hypothesis of character shift due to interspecific competition.