Scanning electron microscopy analysis of the developmental, inter- and intraspecific variation in the otoliths of Anguilla anguilla (Linnaeus, 1758) collected from Bafa Lake in Western Anatolia, Türkiye

Abstract

This study aimed to identify unique traits, grounded in a thorough description of the sagitta otolith of Anguilla anguilla, to characterize its ontogenetic stages between juvenile and preadult individuals. Twenty-one characteristics were designated to investigate the ontogenetic (when comparing the otolith characteristics of fishes of different sizes, interspecific variation (comparing the otolith characteristics of the studied species with those of related species), and intraspecific variation (comparing the otolith characteristics of the studied species with those of the same species from different localities, i.e. geographical variation). This investigation concluded that the sagittal otoliths exhibited ontogenetic disparities based on the shapes recorded by different age groups. Otoliths of the young individuals belonging to fish total length groups GI and GII have shown differences in shape from those of the older individuals in the other seven length groups surveyed. An assessment of previously available otolith descriptions of A. anguilla collected from other areas revealed differences between species across larger geographic areas, making some features unsuitable for further investigation. However, other otolith traits were found to be reliable across different length groups and could be considered species-specific features for identification. These traits include otolith width, otolith thickness, the shape of the mesial and lateral surfaces, the shape of the sulcus acusticus, the presence or absence of ostio-caudal differentiation, and the shape, size, and thickness of the rostrum.