Viability of Allotriploids in Salmonids

Abstract

Six intra-and interspecific crossings were made using three species of salmonids viz. brook trout Salvelinus fontinalis, masu salmon Oncorhynchus masou, and kokanee O. nerka. Then a portion of each of the crosses was heat-shocked at 29°C for ten min duration commencing ten min after fertilization to induce triploidy. Chromosome numbers and/or electrophoretic genotypes at the phosphogluconate dehydrogenase A (Pgdh-A) locus of survivors were examined to determine ploidy. The triploid rate of heat-shocked brook trout was very high, but that of masu salmon was moderate. Viable triploid hybrids were succes sfully produced in the reciprocal hybridizations between brook trout and masu salmon, but survival potentials of allotriploids were not different from those of diploid hybrids. In brook trout ?? ×kokanee ??, all offsprings from normal hybridization died before feeding, while a small number of allotriploids could survive beyond feeding stage. This evidence suggests that inviabilities of diploid hybrids may be moderated by allotriploidization. Only heat-shocked fish survived in the masu salmon ?? ×kokanee ?? hybridization, suggesting in-creased viability of triploids, but the ploidy of the survivors in this group was not determined.