Using otolith morphometry for the identification of three sympatric and morphologically similar species of Astyanax from the Atlantic Rain Forest (Argentina)

In several genera, the otolith shape is species-specific and the use of this structure provides a useful tool aiding in the species identification. In many studies regarding Neotropical fish fauna, species of the genus Astyanax are commonly identified at the genus level, mainly due to the phenotypic plasticity of the morphological characters traditionally used for species determination. In consequence, additional tools intended to better elucidate the taxonomic boundaries between species of Astyanax are certainly needed. In the last decade, the shape of otoliths has allowed to discriminate among closely related species. In this work, Fourier descriptors and shape indices of lapillus otolith were evaluated for the discrimination among three sympatric species of genus Astyanax inhabiting streams of the Atlantic Rain Forest (Argentina). Aspect ratio, roundness and ellipticity of otoliths were significantly different between the species (p < 0.05) while, no significant differences were found for circularity, rectangularity and form factor (p > 0.05). PERMANOVA analysis reveal significant differences between species using Fourier descriptors (F = 96.7, 0.0001 < p < 0.02) and the reclassification rates of quadratic discriminant analysis were high, averaging 86.3% (82.7 - 88.6%). Multivariate analyses of shape indices were not effective to discriminate between species. Instead, high classification percentages suggest that the otolith outline is a potential tool for the identification of sympatric morphologically similar species of Astyanax. Our results could contribute to future taxonomic and phylogenetic studies and may be an interesting input for both paleontological and trophic studies in sympatric species.