Estimates of genetic and phenotypic parameters for length and weight of marine net-pen reared coho salmon (Oncorhynchus kisutch Walbaum)

Heritabilities and genetic and phenotypic correlations were estimated for l ength and weight of two brood years (BY 1977 and BY 1978) of coho salmon [O ncorhynchus kisutch (Walbaum)] during the marine net-pen phase of rearing. The estimates were calculated from length and weight measurements on progen y resulting from a nested mating design and measurements at approximately 4 and 7 months after entering sea water. Point estimate for heritabilities b ased on the sire component for BY 1977 were low to moderate (0.02-0.19) and did not differ significantly from zero. On the other hand, BY 1978 estimat es ranged from 0.31 to 0.62 and, with two exceptions, were significantly di fferent from zero, The latter estimates may have been inflated by inclusion of variances from non-additive sources, but still indicated that differenc es in the genetic potential for increased growth between the two pear class es may be substantial. Genetic correlations between length and weight withi n sampling periods were consistently high (0.95-1.00), indicating that plei otropic gene action or close linkage among genes affects length and weight. Genetic correlations between body size traits (length and weight) between sampling periods varied considerably but suggested a potential for indirect selection gains. Genetic correlation approximations derived using family m eans or ranks appeared to provide reliable estimates and may be useful when environmental influences cause a significant deviation from normality.