GENETIC POPULATION-STRUCTURE OF AMERICAN PLAICE (HIPPOGLOSSOIDES-PLATESSOIDES) FROM THE GULF OF ST-LAWRENCE, CANADA

The genetic population structure of American plaice (Hippoglossoides platessoides) was examined with an electrophoretic analysis of the products of 40 protein-coding loci and with restriction fragment length polymorphisms in mitochondrial DNA. Samples of American plaice collected in the same year from six sites within the Gulf of St. Lawrence showed little heterogeneity in allele frequencies at eight loci. Furthermore, few significant differences in allele frequencies were detected among American plaice collected over three different years from the same site. Also, fish collected from the Grand Banks of Newfoundland showed little genetic differentiation from the Gulf fish. Of the 25 restriction endonucleases used to search for restriction fragment length polymorphisms, only Hind III and Pvu II gave variable fragment patterns. Most fish had the same haplotype and three other haplotypes were represented by two fish at most from each site. American plaice in the Gulf of St. Lawrence appear to be a single, randomly mating population. Large effective population size and high rates of gene flow may account for the observed lack of genetic population subdivision.