Identification and distribution of larvae of redfish (Sebastes fasciatus and S-mentella : Scorpaenidae) in the Gulf of St. Lawrence

Genetic variation at the liver MDH* locus was used to describe the species composition and the geographic distribution of the larvae of the two redfis h species, (Sebastes mentella and S. fasciatus) in the Gulf of St. Lawrence in 1991 and 1992. In both years, redfish larvae were more abundant at the junction of the Laurentian and the Esquiman Channels than in other areas su rveyed. Electrophoretic analysis of 697 larvae in 1991 and 1041 in 1992 sho wed that larvae of both species were present in the Gulf during the two yea rs of the study although in very different proportion. Larvae belonging to the genotype MDH*A1A1 (S. mentella) represented at least 61% of the redfish larvae collected in the Gulf in 1991 and 77% in 1992. Strong spatial heter ogeneity in the frequency of the two MDH* alleles was observed; a higher pr oportion of S. mentella occurred in the central and deeper part of the chan nels and a higher proportion of S. fasciatus in shallower zones. Larvae of the genotype MDH*A1A1 (S. mentella) were significantly larger than those of the genotype MDH*A2A2 (S. fasciatus) for both years of the study, suggesti ng that the extrusion times differ between the two redfish species. The siz es and geographic distributions of the heterozygous larvae (MDH*A1A2) did n ot differ from those of S. mentella (MDH*A1A1).