Restriction fragment length polymorphism of rDNA in the redfishes Sebastesfasciatus and S-mentella (Scorpaenidae) from the Gulf of St. Lawrence

A restriction fragment length polymorphism (RFLP) analysis was carried out on nuclear ribosomal DNA (rDNA) of the redfishes Sebastes fasciatus and Seb astes mentella from the Gulf of St. Lawrence in an attempt to describe new molecular markers that would discriminate these two sibling species. The RF LP analysis revealed heterogeneity in the size of the repeat unit within an d among individuals that is most likely the result of variation in the leng th of the intergenic spacer. Double digestion of rDNA with the restriction enzymes EcoRI and ScaI and subsequent hybridization with a 28S probe reveal ed the presence of three patterns of fragments. Two fragment groups seem to characterize S. mentella and S. fasciatus. Both fragment groups were prese nt in several specimens, suggesting either a restriction-site polymorphism in S. mentella or a hybrid origin for these redfish. Discriminant analysis clearly differentiated all three rDNA patterns. Comparisons of genetic vari ations at the MDH* locus and of the number of soft rays in the anal fin amo ng the three rDNA-defined groups suggest that if the individuals showing th e two groups of fragments are hybrids between S. fasciatus and S. mentella, introgression has also occurred in the Gulf of St. Lawrence.