SURVIVAL TO FRY AND SEAWATER TOLERANCE OF DIPLOID AND TRIPLOID HYBRIDS BETWEEN CHINOOK (ONCORHYNCHUS-TSHAWYTSCHA), CHUM (ONCORHYNCUS-KETA),AND PINK SALMON (ONCORHYNCHUS-GORBUSCHA)

We investigated the viability and seawater tolerance of all possible c ombinations of triploid and diploid hybrids between chinook (Oncorhync hus tshawytscha), chum (O. keta), and pink salmon (O. gorbuscha) in tw o brood years. Triploidy (induced by heat shock shortly after fertiliz ation) was determined by flow cytometry of blood taken from a sample o f the fish. A factorial mating design was used to estimate the effects of cross, heat shock (ploidy), and their interaction. With the except ion of the chinook (female) X chum (male) cross, all combinations prod uced offspring that survived to yolk absorption. Survival of heat-shoc ked groups was lower than that of diploid controls at the eyed stage a nd at hatching, but not different from diploids between hatching and y olk absorption. Induced triploidy did not increase the viability of in terspecies hybrids. The level of triploid induction averaged across al l heat-shocked crosses was 88% in one year and 95% in the other. Seawa ter tolerance (measured by 24-h seawater challenge survival) was highe r in chinook hybrids with pink and chum salmon than in chinook control s. Seawater tolerance did not differ between diploid controls and heat -shocked triploid groups. Combinations that had seawater tolerance sho rtly after yolk absorption include chinook x pink, pink x chinook, and chum x chinook.