GENETIC, ENVIRONMENTAL AND INTERACTION EFFECTS ON THE INCIDENCE OF JACKING IN ONCORHYNCHUS-TSHAWYTSCHA (CHINOOK SALMON)

Jacking in chinook salmon, Oncorhynchus tshawytscha, is defined as sexual maturation of males after at least 1 year in sea water, occurring 1 year prior to any of the females of the same cohort. A breeding experiment was carried out with jack and non-jack sires nested within six dams. The resulting 12 families were reared under two different temperatures for the first part of their lives to test for the effect of early developmental acceleration on jacking rates. Significant sire age (jack vs. non-jack), dam and environment (water temperature) effects were found for the incidence of jacking. Significant genotype-by-environment interactions were also found, indicating that accelerated early development does not increase jacking rates uniformly across all genotypes. There were no significant correlations between mean family growth- and size-related variables and the observed jacking rates. Heritability estimates based on intra-dam sire-offspring regressions were 0.48 (+/- 0.24) and 0.32 (+/- 0.14) for the accelerated and non-accelerated family groups, respectively. The results of sib-analysis heritability calculations indicated large dominance effects or sex linkage. The genetic component to jacking found in this study for chinook salmon was greater than has been generally reported for age of first maturation in salmonids.