Survival to Fry and Seawater Tolerance of Diploid and Triploid Hybrids between Chinook (Oncorhynchus tshawytscha), Chum (O. keta), and Pink Salmon (O. gorbuscha)

Abstract

We investigated the viability and seawater tolerance of all possible combinations of triploid and diploid hybrids between chinook (Oncorhynchus tshawytscha), chum (O. keta), and pink salmon (O. gorbuscha) in two brood years. Triploidy (induced by heat shock shortly after fertilization) was determined by flow cytometry of blood taken from a sample of the fish. A factorial mating design was used to estimate the effects of cross, heat shock (ploidy), and their interaction. With the exception of the chinook (♂) × chum (♀) cross, all combinations produced offspring that survived to yolk absorption. Survival of heat-shocked groups was lower than that of diploid controls at the eyed stage and at hatching, but not different from diploids between hatching and yolk absorption. Induced triploidy did not increase the viability of interspecies hybrids. The level of triploid induction averaged across all heat-shocked crosses was 88% in one year and 95% in the other. Seawater tolerance (measured by 24-h seawater challenge survival) was higher in chinook hybrids with pink and chum salmon than in chinook controls. Seawater tolerance did not differ between diploid controls and heat-shocked triploid groups. Combinations that had seawater tolerance shortly after yolk absorption include chinook × pink, pink × chinook, and chum × chinook.