Increased resistance of triploid rainbow trout × coho salmon hybrids to infectious hematopoietic necrosis virus

Abstract Diploid and heat-induced triploid treatment groups of rainbow trout ( Salmo gairdneri ), coho salmon ( Oncorhynchus kisutch ), and reciprocal hybrid crosses were produced and monitored for survival and growth through early life stages. Survival to the fry stage showed a significant increase in the triploid rainbow trout female × coho salmon male hybrids relative to the diploid hybrid group. At a mean weight of 0.65 g all groups were administered a standardized static bath challenge with Leong Type 2 virulent IHN virus. The triploid rainbow trout female × coho salmon male hybrids showed a significant increase in IHN resistance when compared to pure-species rainbow trout groups. Early growth results suggest a poorer growth rate for the triploid hybrid. Triploid hybridization improved viability of the hybrid cross, increased relative resistance to IHN virus challenge, and may provide a useful method for the interspecific transfer of desired characters into commercial fish stocks.