First evidence of otolith abnormalities in Belone belone from the Sea of Marmara: An integrative approach to morphological deformities with light and scanning electron microscopy

This study is the first of its kind, providing detailed evidence of otolith abnormalities in Belone belone in the Darıca coast of the Sea of Marmara (Türkiye), using an integrative approach that combines light microscopy and scanning electron microscopy (SEM). Structural anomalies in otoliths were detected across both sexes, and 4% of B. belone individuals analyzed were found to suffer from abnormal otoliths. In contrast, distinct differences were detected between normal and abnormal otoliths. Although there were some differences between morphometric parameters, a statistically significant difference was determined only in terms of otolith perimeter. SEM and light microscopy revealed that morphological differences, especially on the lateral otolith surfaces, were key to distinguishing normal and abnormal otoliths. Normal otoliths exhibited typical anatomical features such as aragonite crystal structure, elliptic-lanceolate shape, short-wide rostrum, and generally indistinct antirostrum. In contrast, abnormal otoliths exhibited a high degree of shape variability, with irregular surface protrusions, pits, and disorders in the crystal structure resulting from calcium carbonate polymorphism. The wide range of morphological anomalies observed in B. belone across sizes and sexes suggests a potential link to environmental stressors, such as mucilage and pollution, as well as genetically driven developmental disorders.