Application of otolith shape analysis to species separation in silversides (Odontesthes, Atherinopsidae) from South America and the South Atlantic Ocean

Argentina has one of the largest numbers of species of the genus Odontesthes that coexist in the world (Odontesthes argentinensis, O. platensis, O. smitti, O. nigricans, O. incisa, O. bonariensis and O. hatcheri). These species have an important ecological role in the trophic webs in the region and in commercial fisheries. However, due to the number of species of the genus Odontesthes, the identification of otoliths in feces and stomach contents of ichthyophages is difficult, as well as in fisheries where the different species are commercialized under the same common name. The aim of this study is the use of otolith shape outline as a morphometric tool for the identification of seven silverside species that coexist in marine and freshwater environments of Argentina. Otolith sagittae of 387 silverside specimens were processed using ShapeR package (R statistical software). The Wavelet coefficients (WCs) and Fourier descriptors (FDs) obtained were analyzed using multivariate methods. Results show that the percentage of correctly classified silversides considering WCs, FDs and WCs and FDs together were 71.83 %, 78.81 %, and 88.63 % respectively. There are significant differences among the otolith shape outline of these species (PERMANOVA test, p < 0.0001). O. platensis, O. argentinensis, O. smitti and O. bonariensis otoliths have elongated shapes, while those of O. nigricans and O. incisa are rounded. Shape differences in the otolith’s antero-posterior axis (rostrum-antirostrum) and posterior end are the more important for species differentiation. Results could contribute to the identification of these species of silversides in dietary studies of ichthyophages and for the identification of the species marketed jointly under the name of silverside on which specific fishing measures could be carried out.