Variation in head morphology in the electric knifefish Apteronotus brasiliensis (Reinhardt, 1852) (Gymnotiformes: Apteronotidae) in the Paraná and São Francisco River Basins

Abstract

Specimens of Apteronotus brasiliensis from Paraná and São Francisco River basins (Brazil) present snout always moderately elongated, that can be oblique or directed forward or strongly downward. Detailed examination revealed that these head-morphology differences are related to individual variation, not to sex, ontogeny or geographic distribution. Keywords: freshwater, morphology, Neotropical fish, Ostariophysi, Teleostei, systematics.