Different sagitta otolith morphotypes for the whitemouth croaker Micropogonias furnieri in the Southwestern Atlantic coast

Otoliths are part of the auditory system of teleostean fishes, and are species-specific structures that may have intraspecific variation depending on the environmental conditions at a regional scale. The main aim of this study was to assess changes in otolith shape of Micropogonias furnieri along its geographical distribution range between the tropical and warm temperate coastal of Southwestern Atlantic. Ten otoliths from each of six areas along the South American coast were examined:1) Rio de Janeiro State (23°S); 2) São Paulo State (24°S); 3) Santa Catarina State (27°S), 4) Rio Grande do Sul State (32°S); 5) Uruguayan coast (35°S); 6) Northern coast of Argentine (39°S). The sagitta otolith contour and shape were characterized using the Elliptical Fourier Analysis (EFA) and the morphometric measurements of both otoliths and respective sulcus acusticus were performed using the software ImageJ. Variations of otolith shape were assessed by five explanatory variables (area, perimeter, width, circularity and the maximum Feret diameter) and a Principal Components Analysis (PCA) was applied to Elliptical Fourier Descriptors. We found significant differences in area, perimeter and circularity of otoliths. Clustering the range of the 30 first harmonics using Ward's hierarchical algorithm yielded three otolith morphotypes. Plots of the two first Principal Component (PCs) axes for the 60 examined otoliths did not discriminate the population distribution along the six areas. The three different otolith morphotypes do not seem to be subjected to a clinal variation for this transition area in the Southwestern Atlantic, and suggest an overlap of individuals of different stocks/populations mixing along their geographical distribution range favored by their eurythermic and euryhaline characteristics.