Effect of Allotriploidization on Development of the Hybrids between Female Chum Salmon and Male Brook Trout

Abstract

Mature ova of chum salmon Oncorhynchus keta were inseminated with milt from brook trout Salvelinus fontinalis and a portion of the eggs were treated with hydrostatic pressure in order to block the second polar body extrusion and to induce allotriploidy. The embryos from eggs exposed to the hydrostatic pressure shock were more viable than embryos from the usual hybridiza-lion. Karyological studies revealed that the latter inviable hybrids had exactly the same inter-mediate diploid karyatype as that of between two parental species, while the former viable hybrids had the allotriploidy comprising two sets of the maternal haploid complement and one set of the paternal haploid complement. A small number of viable larvae which occurred in the usual hybridization were found to be spontaneous allotriploids in biochemical studies using isozymes as gene markers. These facts proved that allotriploidization can lead to increased survival of developing embryos in some hybridization between salmonid species.