Background. The annular seabream, Diplodus annularis (Linnaeus, 1758), is the most common sparid fi sh in the Mediterranean Sea. This species is widespread in Tunisia. Despite their economic importance, due to their excellent white and delicate fl esh (demersal fi sh) and their signifi cant size, few studies have hitherto focused on stock discrimination and on the fi sheries management. The goal of this research was to evaluate the stock structure of D. annularis for two Tunisian insular populations based on the otolith shape, using different statistical approaches. Materials and methods. The specimens of Diplodus annularis were collected during fi ve months ranging from May through September 2014 at two sites: Djerba and Kerkennah. In total, 120 fi sh were collected from the two sites: 60 specimens of each population (30 males and 30 females) and were included in different statistical analyses. The Fourier coeffi cients were determined to evaluate the degree of similarity in the otoliths and detect the reciprocal variability. Results. By comparing the two studied populations, we revealed statistical signifi cant differences, an asymmetry (left-right), of otoliths (P < 0.05). In the same population, symmetry (left-right) was detected for the males, females of Kerkennah, and females of Djerba. However, an asymmetry was detected only for the males of Djerba. Also, sexual dimorphism was observed only for the Djerba population. Conclusion. The comparison of the otolith morphology of the two populations showed a clear difference in shape and a left-right asymmetry of otoliths. This asymmetry indicates that the two populations belong to different stock of fi sh. The stocks characterization is considered as an important tool for fi sheries management. Further studies are necessary to determine the origin of the otolith shape differences and whether they are related only to environmental conditions or a genetic basis may also be responsible.

Background. The thinlip grey mullet, Liza ramada (Risso, 1810), is widespread in Tunisia. Despite its economic importance, the stock discrimination of this fish is poorly understood. The aim of this study is to investigate, for the first time, the stock discrimination of this species for two Tunisian populations based on the otolith shape, using different statistical approaches. Materials and methods. The specimens of L. ramada were collected during three months (from March to May 2013) at two sampling sites: the marine (Cap Zebib sea resort) and the estuarine (Mellegue Dam) in Tunisia. We analysed sagittal otolith shape variation for 120 individuals (60 fish of each study site comprising 30 males and 30 females) for both sexes (males and females) and two sides (left and right otolith) for each specimen. Results. Statistical-and discriminant function analysis of the sagittal otolith shape clearly demonstrated statistically significant differences from the two populations. These results were also confirmed by highly statistically significant difference between otolith shape (left and right) for both sexes. An asymmetry was detected when comparing otoliths of the same side (RR-LL) between different sampling sites. Conclusion. The shape variability of otolith between these two sampling sites is probably correlated with local environmental and ecological factors.