Stock discrimination of the bogue, Boops boops (Actinopterygii: Perciformes: Sparidae), from two Tunisian marine stations using the otolith shape

Abstract

Background. The bogue, Boops boops (Linnaeus, 1758), is the most common sparid fish in the Tunisian waters. Despite its economic importance, the stock discrimination of this species is poorly understood up to date. As the otolith shape has long been known to be species-specific and recent studies have shown its value as an indicator of stock identity, the presently reported study was carried out for the first time to investigate the discrimination of the stock structure of B. boops samples collected from two sampling sites at the marine stations of Monastir and Zarzis located in northern Tunisia using the otolith shape descriptors analysis. Materials and methods. A total of 183 adult samples of B. boops were collected between January and August 2019 from two sampling sites at the Monastir and Zarzis marine stations. The outlines of sagittal otolith pairs from fish samples collected from the two sites were digitized and analyzed for shape variation by elliptical Fourier analysis (EFA). Results. Discriminant Function Analysis (DFA) showed statistically significant differences in otolith shape within and between fish samples in the two sites, i.e., there was an asymmetry. This asymmetry was found between the left and right otoliths within each site, as well as between the same sides (left–left) and (right–right) otoliths between the Monastir and Zarzis stations. Conclusion. Fish stock samples at the two stations represent two groups or populations of the Tunisian bogue stock and should be managed separately. In addition, the asymmetry in the otolith shape between fish samples from the two stations can be attributed to differences in the rate of growth resulting from local environmental factors such as water temperature, salinity, habitat, and diet. However, the inter-individual or even the intra-population asymmetry between the right and left otoliths can be explained by the possibility of having intra-individual stress that led to abnormalities in the development of the individuals or by the presence of poor living conditions for the larvae, resulting from unfavorable environments.

Keywords

• Boops boops
• elliptic Fourier descriptors
• otolith