Heterogeneity in the body size of Ontario cultured rainbow trout with different mitochondrial DNA haplotypes

Abstract

Body sizes of rainbow trout ( Oncorhynchus mykiss) with different mitochondrial DNA (mtDNA) haplotypes were compared in four commercial strains reared in Ontario. A total of 565 fish derived from five spawning collections were analyzed for the association between weight, length, and condition factor and mtDNA haplotype. All the collections were derived from the fall-spawning group within the commercial strains and represented the pooled contribution from 1 week's spawning effort. Three strains had similar mtDNA haplotypic compositions which differed from the fourth strain. Significant heterogeneity in body size of fish with different mtDNA haplotypes was observed in two strains. Fish with haplotypes 1 and 4 were significantly larger, and had higher condition factors compared to haplotype 10 and 13 fish. Comparisons with haplotypes 1 and 4 were not possible in the other two strains due to the absence or low frequency of these haplotypes. These results suggest that the relative efficiencies of selection programs may be enhanced by selecting haplotype 1 and 4 fish compared to fish with similar growth rates from the general population (i.e. haplotype 1 and 4 fish appear to have increased breeding values for growth compared to the population mean).