Sexual maturation and fertility of diploid and triploid Atlantic salmon X brown trout hybrids

Abstract

Hybrids between Atlantic salmon ( Salmo salar, At) and brown trout ( Salmo trutta, Bn) are highly viable and expected to be functionally sterile due to major interspecific karyotypic differences. However, contradictory results in published reports have left questions about the fertility of these hybrids. We produced backcrosses between male diploid, male triploid, and female diploid F, At X Bn hybrids and both parental species. Additionally, half of the eggs from each cross were heat-shocked to induce second polar body retention. The hybrid nature of the F 1 broodstock and the backcross progeny was confirmed with protein electrophoretic analyses, including use of two loci (FDHG ∗ and PGK-2 ∗) heretofore unreported as diagnostic for these species. These crosses produced either non-viable or sterile triploid progeny. Introgression between the two species' genomes via hybridization appears to be effectively blocked. Use of sterile diploid or triploid salmonid hybrids in commercial culture could have economic advantages and mitigate concerns regarding escape and establishment of domesticated fish stocks or interbreeding with wild stocks.