Environmental effects on otolith morphology variability of European eel, Anguilla anguilla (Linnaeus, 1758), for subpopulation discrimination in Corsica

Otolith shape analysis is an efficient tool for fish stock identification. However, due to insufficient research, it remains still poorly understood concerning the European eel ( Anguilla anguilla ), a highly migratory catadromous and panmictic species. The aim of this study is to discriminate the subpopulations of A. anguilla from rivers and two lagoons (three sites) from Corsican continental waters using morphological variations in otolith shape. The otolith shape was described by indices of shapes and by geometric morphometric shape, to understand how otolith morphology changes with eel growth and across contrasting habitats. In this study, the shape of each otolith (N = 305) was described with one landmark and ninety-nine semi-landmarks and by eight shape indices (form factor, aspect ratio, ellipticity, circularity, roundness, rectangularity, squareness and solidity). Results indicate that otolith shape is highly marked for the larger compared to smaller sizes, particularly for the individuals from the lagoons. The slight differences in the small otoliths appear to be due to the acquisition of the shape during the glass eel stage in the marine environment whereas the difference marked in the shape of the large otoliths would be due to the variability of environmental conditions, underlying marked change in otolith shape during growth.