Research Article: Discriminant stock structure of Diplodus annularis (Perciformes, Sparidae) in Tunisian waters inferred from saccular otolith morphometry and microchemistry

We studied the size dimensions and microchemical structure of the saccular otoliths (sagittae) of two populations of the annular seabream (Diplodus annularis) collected from the Djerba and Kerkennah Islands in Tunisian waters. The goals of our study included (1) measuring the otolith’s length (Lo), width (Wo), surface area (Ao), and perimeter (Po), and evaluating differences in these characteristics and microchemical elements between individuals of D. annularis within each Island, (2) exploring how potential fluctuating asymmetry (FA) in the otolith size affects the stock structure of D. annularis in two Islands, and (3) using these findings to recognize if there were distinct stock structures and connectivity between fish within the two Islands, to develop better-guiding policies for managing and governing the fishery within these Islands. The results revealed significant asymmetry in all size dimensions between the left and right otoliths among males and females within the Djerba and Kerkennah Islands and males and females between the two Islands due to FA. In addition, significant differences in otolith contents of K, Cs, and Pb were found between individuals of the two Islands. The significant asymmetry in otolith size dimensions among males and females of the two Islands due to FA and the noticeable difference in otolith microchemical elements between individuals of the two groups were attributed to some factors, such as fish age, environmental conditions, and fish biological traits. Therefore, the results confirmed the discriminant stock structure and limited connectivity between fish within the two Islands, which should be managed separately.