Genetic characterization of wild and suspension-cultured blue mussels (Mytilus edulis Linneaus, 1758) in the Magdalen Islands (southern Gulf of St. Lawrence, Canada)

The genetic characteristics of wild and suspension-cultured blue mussels fr om three lagoons of the Magdalen Islands were determined from the study of seven enzyme loci. Only 3.5% of mussels scored at the MPI* locus were ident ified as Mytilus trossulus, For M. edulis, no major differences could be de tected in allelic frequencies of wild mussels within and among the lagoons, indicating that gene flow around the Magdalen Islands is high. High levels of gene flow are also inferred from the high F-st and N(e)m values. Tempor al stability is suggested by homogeneity in allelic frequencies of mussels from different size classes (assumed to represent different cohorts) sample d within each lagoon, An important heterozygote deficiency was observed in wild mussels from the House Harbour and the Great Entry lagoons where the m ean Ho was 0.34 and 0.32, respectively. In contrast, there were no signific ant heterozygote deficiencies or excesses at most loci in wild mussels from Amherst Basin whose Ho = 0.50. The degree of heterozygosity was significan tly higher in the wild mussels from Amherst Basin than in those from the ot her two lagoons. Significant decreases in the degree of heterozygosity were observed in suspension-cultured mussels 1 and 2 y after their transfer as spat from Amherst Basin to grow-out sites in the Great Entry and the House Harbour lagoons. One possible explanation for the observed decreases in the degree of heterozygosity is that a substantial number of heterozygotes col lected in Amherst Basin may be lost through fall-off during suspension-cult ure activities, as suggested by the lower mean heterozygosities of sleeved mussels at both grow-out sites (mean Ho = 0.35-0.38).