SEXUAL-MATURATION AND FERTILITY OF DIPLOID AND TRIPLOID ATLANTIC SALMON X BROWN TROUT HYBRIDS

Hybrids between Atlantic salmon (Salmo salar, At) and brown trout (Sal mo trutta, Bn) are highly viable and expected to be functionally steri le due to major interspecific karyotypic differences. However, contrad ictory results in published reports have left questions about the fert ility of these hybrids. We produced backcrosses between male diploid, male triploid, and female diploid F-1 At X Bn hybrids and both parenta l species. Additionally, half of the eggs from each cross were heat-sh ocked to induce second polar body retention. The hybrid nature of the F-1 broodstock and the backcross progeny was confirmed with protein el ectrophoretic analyses, including use of two loci (FDHG and PGK-2*) h eretofore unreported as diagnostic for these species. These crosses pr oduced either nonviable or sterile triploid progeny, Introgression bet ween the two species' genomes via hybridization appears to be effectiv ely blocked, Use of sterile diploid or triploid salmonid hybrids in co mmercial culture could have economic advantages and mitigate concerns regarding escape and establishment of domesticated fish stocks or inte rbreeding with wild stocks.