Pagellus erythrinus ( Fassatoui et al., 2009 )

Kaouèche, Myriam, Bahri-Sfar, Lilia, Hammami, Ibtissem & Ben Hassine, Oum Kalthoum, 2013, Morphological and genetic variations of Diplodus vulgaris along the Tunisian coasts, Cybium 37 (1 - 2), pp. 1-2 : 112

Pagellus erythrinus ( Fassatoui et al., 2009) . Finally, in the case of Diplodus sargus , a differentiation was revealed by allozymes and was attributed to small-scale, not patterned, genetic heterogeneity among local populations, whereas the mtDNA data indicate a genetic homogeneity of the white seabream populations among the same localities across the STS ( Kaouèche et al., 2011).

In addition, a sufficient degree of isolation may result in notable morphological differentiation among stocks within a species ( Pepin and Carr, 1993). Beside the primary interest in understanding the patterning of fish populations, the description of the morphological variation between populations and the identification of correlated degree of genetic pattern help to implement the appropriate management strategies of Mediterranean fisheries. In this context, morphometric characters ( Turan and Basusta, 2001; Palma and Andrade, 2002; Turan, 2004; Bahri-Sfar and Ben Hassine, 2009; Hammami et al., 2011) or morphometric characters associated to genetic data ( Cabral et al., 2003; Mejri et al., 2012) have been commonly used as markers to characterize and delimit geographic stocks ( Arculeo et al., 2003).

The two-banded seabream, Diplodus vulgaris is one of the most frequent and abundant sparid in the Mediterranean Sea and along the eastern Atlantic coast ( Bauchot and Hureau, 1986). The species is generally found associated with both rocky and sandy bottoms. Juveniles inhabit coastal lagoons and estuaries ( Macpherson, 1998). D. vulgaris life cycle is characterized by an offshore pelagic larval dispersion during 29-58 days followed by a nectobenthic adult phase. These characteristics give great dispersal potential, since in marine environments, early-life-history traits and dispersal capabilities may influence exchanges of gene flow between populations (Palumbi, 2004; Galarza et al., 2009).

In this context, we have undertaken the characterization of Mediterranean populations of two-banded seabream across the STS. Effectively, despite the commercial importance of this species, studies are scarce. In this regard, a first genetic study of Mediterranean Diplodus vulgaris populations, using allozyme markers in seven samples from Tyrrhenian, Aegean, Ionian and Adriatic Seas and also both sides of the STS, demonstrated a distinction of the Adriatic Sea sample only ( Arculeo et al., 2003). However, Galarza et al. (2009) have shown a genetic transition across the Almeria-Oran front using microsatellite markers, but with sampling that did not cover the entire distribution area of D. vulgaris in the Mediterranean Sea. In the present study, we aimed to check whether morphological variation in D. vulgaris was in relation with the STS, then we examined the possible correlation with genetics and ecological features of the studied populations. For that purpose, we collected samples along the Tunisian coasts, on both sides of the STS in order to characterize the population of D. vulgaris in this transition area with heterogeneous environments. The morphometric study was based on body shape descriptors (conventional linear and truss measurements), while genetic investigation was based on allozyme polymorphism.