Abstract
Significant body shape differences were observed between two commercially important redfish species Sebastes fasdatus and Sebastes mentella , in the Gulf of St Lawrence, first classified according to the variability at the MDH‐A* locus, a diagnostic criterion for the two species in allopatry. The observed sexual dimorphism was probably related to the presence of gravid females in the sample. Sebastes mentella appeared to be more fusiform than S. fasdatus , a characteristic that may reflect the more pelagic behaviour of S. mentella . The body shape of their hybrids was closer to that of S. mentella . Similarities between hybrids and S. mentella were also observed for meristic characteristics and depth distribution. The implications of these similarities for introgression are discussed. Body shape variability of specimens of hybrid origin was greater than that of either parental species, with features ranging from S. mentella‐like to S. fasciatus ‐like. The role of introgression in generating morphological variability is emphasized.