EVIDENCE FOR INHERITANCE OF AGE OF MATURITY IN CHINOOK SALMON (ONCORHYNCHUS-TSHAWYTSCHA)

We report results of age-specific mating experiments carried out with chinook salmon (Oncorhynchus tshawytscha) at Elk River Hatchery, Orego n. Our analysis of returns from these experiments includes assessment of the marine growth of progeny, and we also account for the negative bias on mean age of returning mature progeny that is a consequence of troll fishery harvest of immature salmon. Results suggest that (a) her itability of age of maturity is relatively high in this species (calcu lated h2 were 0.49-0.57 and 0.39-0.41 for males and females, respectiv ely), (b) inheritance of age of maturity of females appears to be inde pendent of age of male parent, and (c) for a given parental age, ''fas ter-growing'' progeny generally mature at younger ages, but (d) progen y from older parents are not generally smaller at age than progeny fro m younger parents. Inheritance of age of maturity therefore cannot be a simple reflection of inheritance of growth rate. We tentatively prop ose the existence of heritable minimum threshold lengths that differen tially trigger maturation according to age and sex of parents. We also consider the significance of these experiments for artificial propaga tion of this species,