Growth and genetic variation in hatchery-reared larval and juvenile Dover sole, Solea solea (L.)

The variation in multiple-locus and single-locus heterozygosity, and its co rrelation with growth rate, were examined in laboratory-reared juvenile Dov er sole from two populations. The genetic structure of the populations was examined to test for genotype differences among individuals surviving past metamorphosis (70 days after hatching). Using enzyme electrophoresis, speci mens were examined for 14 scorable loci, seven of them polymorphic. Larval growth rate was significantly affected by rearing treatment, but difference s between treatments declined with age. Larvae from broodstock originating from the Irish Sea sole were larger at hatching, grew faster, and initiated metamorphosis earlier than larvae from broodstock originating from the Ska gerrak-Kattegat Norwegian sole. The groups were indistinguishable on the ba sis of multilocus or single-locus heterozygosity and allele or genotype fre quencies, after metamorphosis. Three measures of genetic diversity (percent age of loci polymorphic, number of alleles per locus and heterozygosity) we re considerably lower than those of wild populations; batches from these so le hatcheries clearly demonstrated loss of genetic diversity, and marked ch anges in gene frequencies of cultured batches relative to the wild populati ons from which the parents were derived. Only two loci in the Norwegian sam ple were deficient in heterozygotes, whereas others exhibited heterozygote excess. These heterozygote excesses did not seem to be related to a particu lar allele or alleles. There was little evidence in this data set that the degree of multilocus or single-locus heterozygosity correlates with growth rate in S. solea. This conclusion agrees with the general observation that the correlation is not expected in populations where there is no heterozygo te deficiency. (C) 1999 Elsevier Science B.V. All rights reserved.