375 



Abstract.— Genetic variation at the 

 liver MDH* locus was used to describe 

 the species composition and the geo- 

 graphic distribution of the larvae of 

 the two redfish species, iSebastes men- 

 tella and S. fasciatus) in the Gulf of St. 

 Lawrence in 1991 and 1992. In both 

 years, redfish larvae were more abun- 

 dant at the junction of the Laurentian 

 and the Esquiman Channels than in 

 other areas surveyed. Electrophoretic 

 analysis of 697 larvae in 1991 and 1041 

 in 1992 showed that larvae of both spe- 

 cies were present in the Gulf during the 

 two years of the study although in very 

 different proportion. Larvae belong- 

 ing to the genotype MDH*A1A1 iS. 

 mentella) represented at least Gl'^r of 

 the redfish larvae collected in the Gulf 

 in 1991 and 77'r in 1992. Strong spa- 

 tial heterogeneity in the frequency of 

 the two MDH* alleles was observed; a 

 higher proportion of S. mentella occur- 

 red in the central and deeper part of the 

 channels 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. fascia- 

 tus) for both years of the study, sug- 

 gesting that the extrusion times differ 

 between the two redfish species. The 

 sizes and geographic distributions of 

 the heterozygous larvae (MDH*A1A2) 

 did not differ from those of S. mentella 

 [MDWAIAD. 



Identification and distribution of larvae of 

 redfish iSebastes fasciatus and 5. mentella: 

 Scorpaenidae) in the Gulf of St. Lawrence 



Jean-Marie Sevigny 



Direction des Invertebres el de la Biologie expenmentale 



Institut Maunce-Lamontagne 



Ministere des Peches et des Oceans 



850 Route de la Mer 



Mont-Joli 



Quebec G5H 3Z4, Canada 



E-mail address Sevignyimadfo-mpogcca 



Patrice Gagne 



Departement de Biologie 

 Faculte des Sciences et de Genie 

 Universite Laval 

 Quebec GIK 7P4, Canada 



Yves de Lafontalne 



Environment Canada 



Centre Saint-Laurent, 105 McGill, suite 7400 



Montreal, Quebec H2Y 2E7, Canada 



Julian Dodson 



Departement de Biologie 

 Faculte des Sciences et de Genie 

 Universite Laval 

 Quebec GIK 7P4, Canada 



Manuscript accepted 26 November 1999. 

 Fish. Bull. 98: 375-388 (2000 1. 



The Gulf of St. Lawrence redfish 

 consist of a complex of three puta- 

 tive species, currently identified as 

 deepwater redfish, Sebastes men- 

 tella, and Acadian redfish, S. fascia- 

 tus, that dominate the commercial 

 fishery (Atkinson, 1984; 1987;Rubec 

 et al., 1991) and golden redfish, S. 

 norvegicus, formerly named S. mari- 

 nus (Fernholm and Wheeler, 1983) 

 which occurs only sporadically and 

 at very low abundance, namely at 

 <l'7f of the catch (Ni and McKone, 

 1983;Rubecetal., 1991). 



Although S. fasciatus differs mor- 

 phologically from S. me/i tella, the 

 overlap in meristic and morpho- 

 metric characters is such that the 

 two redfish species are difficult to 

 separate and, frequently, individuals 

 cannot be unequivocally identified 



(Ni, 1981; 1982; Kenchmgton. 1986; 

 Rubec et al., 1991). Discrimination 

 among redfish larvae is even more 

 complex because the morphological 

 characters used for adults and juve- 

 niles cannot be used for identifying 

 species during the larval stages 

 (Penney, 1987). The taxonomic con- 

 fusion, as well as the absence of 

 reliable morphological characters to 

 identify the larvae, has limited our 

 understanding of the ecology and 

 population dynamics of redfish in the 

 North Atlantic. 



Electrophoretic analysis is an ap- 

 propriate tool for identifing Sebas- 

 tes species at all stages of their 

 life cycle, including larvae (Payne 

 and Ni, 1982; McGlade et al., 1983; 

 Nedreaas and Naevdal, 1991; Rubec 

 et al., 1991; Seeb and Kendall, 1991; 



