The marble trout (Salmo marmoratus) is an endangered species in Slovenia (and in Italy, Croatia and Albania) because of hybridization resulting from intensive stocking. Eleven populations of trout from the Soca river basin (Slovenia) were analysed using 31 presumptive enzyme loci. Three European control samples representing the main European genotypes of brown trout were also analysed. This analysis con®rmed the existence of extensive hybridization in the main river, resulting in an equal mixture of alleles belonging to marble trout, and Danubian and Atlantic brown trout (Salmo trutta). Despite the high level of introgression observed in the main Soca River, nearly pure populations of marble trout were found in the headwaters of ®ve tributaries. The ®ve stations with pure marble trout will be the basis of a rehabilitation programme. Hardy±Weinberg and linkage disequilibria were observed and hypotheses are discussed to explain this. A scenario for the colonization of the Adriatic region is proposed.

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Analysis of trout from 13 stations on the Mediterranean slopes of the French Pyrenees by 31 presumptive enzyme loci demonstrated the major impact of restocking programmes. Although the annual introgression resulting from these introductions was small, the accumulation of genes of Atlantic origin has resulted in a change in allele frequencies. Genetic disequilibria within and between loci exist. Introgression by genes of domestic (hatchery) origin varied from 0 to 77% among stations. Natural Mediterranean populations show no detectable geographical structure. There was a direct relation between the degree of introgression and heterozygosity. However, restocking could not explain all of the observed genetic disequilibria. 2000 The Fisheries Society of the British Isles

International audienceIn 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