Abstract
In the subfamily Sicydiinae of the family Gobiidae, the species Sicyopterus lagocephalus is one of the common amphidromous fish inhabiting island freshwaters in a large intertropical area, widespread from the Comoros archipelago to the Austral Islands. Eight of the main perennial rivers of La Réunion Island (Mascarene Islands) were sampled in 2000, in order to describe their population genetic structure. A total of 267 adult specimens of S. lagocephalus were screened for 14 enzymatic systems providing 15 presumptive loci, 11 of them being polymorphic. Four other loci were useful as diagnostic markers between S. lagocephalus and Cotylopus acutipinnis, a similar, closely related sympatric species. Both species constitute an economic resource locally called “bichique”. The focus of this study, S. lagocephalus, accounts for the majority of the bichique. The results clearly showed a genetic homogeneity among the eight samples (Fst tests). Within-samples tests (Fis) indicated, in general, a heterozygote deficiency. The multidimensional diagrams (CA) describe an overall structure composed of two main subgroups. This structure was not confirmed in a 2001 sampling. The interpretation of the results takes into account the biological life cycle of this species, characterized by a planktonic phase, from hatching to recruitment, followed by a freshwater life of the adults. All the samples in the survey belong to a single pool. However, the young fish entering the rivers are probably of complex origin. We did not find any isolation between rivers and this result should be considered when conservation measures are taken to prevent overfishing.