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International audience; Ce poster fournit des premiers élements sur la recolonisation de la Seine par le saumon atlantique. 7 individus ont été caractérisés du point de vue génétique à partir 17 marqueurs microsatellites afin d'identifier leur population d'origine probable. Les résultats montrent que les poissons analysés proviennent en partie d'un stock voisin et en partie de populations lointaines.

National audience

National audience

International audience

International audience

International audience

International audience

International audience

The Working Group on the Application of Genetics in Fisheries and Mariculture (WGAGFM) met in La Rochelle, France from 10-12 March, 2003. Seven persons representing six countries were present. Three terms of reference (ToR) were addressed, while one was deferred until the appropriate information was available for review. WGAGFM first considered ToR a) Review and report on the practical use of genome mapping in aquacultured organisms. Genome maps are used extensively in the production of selected strains of agriculture plants and livestock. Studies on the genome of aquatic animais have been summarised in the WG report. Genome mapping projects in aquaculture exist for most major species and linkage maps are now becoming available. WGAGFM produced four recommendations

The genetic structure of two native Silurus aristotelis (one of Europe" s oldest surviving freshwater fish species) populations was investigated using eight microsatellite loci. Average values of population heterozygosity were very high, even approaching values reported for marine fishes, possibly due to stable population sizes and the prolonged undisturbed conditions prevailing in the lakes that represent the native distribution of S. aristotelis. The success of an attempt to introduce the species into a new environment was also evaluated. No loss of genetic variability in the introduced population was detected. Additionally, assignment tests and trees based on genetic distances among individuals indicated the low differentiation of the translocated population from its donor population, and, differentiated the two autochthonous populations successfully. Comparisons with previous allozyme and mitochondrial RFLP studies were also made and showed that results on relative levels of genetic variability among populations were in good agreement among all methods. However, microsatellite analysis exhibited higher power of statistical tests for differentiation among population samples compared to allozymes. Aquatic Living Resources

A sample of African Clarias catfishes from the Senegal River was studied using morphometry, allozyme variation, microsatellites and RFLPs of mitochondrial DNA. They all confirmed the presence of two species, C. gariepinus and C. anguillaris. The two species were closely related genetically and no diagnostic loci were found in allozymes and microsatellites studies. Two of the 11 haplotypes of mtDNA observed were shared by both species. Three of the four assays (morphometry, allozymes and microsatellites) allowed a precise characterization of both. One specimen occupied an intermediate position in the analysis of the data; it was considered an F1 hybrid whose possible origin is discussed.

An electrophoretic study of enzyme polymorphism was conducted on five species of tilapia of the genus Oreochromis: O. niloticus, O. aureus, O. mossambicus, O. urolepis hornorum and O. macrochir. For O. niloticus, five farmed populations were analyzed, as well as two natural populations from the Volta and the Niger rivers. Eighteen enzyme systems, coded by 30 loci were studied. Heterozygosity and genetic distances between the different samples were calculated. The study of the genetic diversity of O. niloticus, shows the resemblances and dissimilarities that exist among these populations, as well as the maintenance of variability in farmed stocks. Analysis of the results obtained for one of the populations of O. aureus and O. mossambicus suggests a case of genetic introgression due to the continued use of these populations in interspecific hybridization. An analysis was conducted to estimate phylogenetic relationships between the different populations.