Asymmetry of post-F1 interspecific reproductive barriers among brown trout (Salmo trutta) and Atlantic salmon (Salmo salar)

F1 hybrids of Atlantic salmon Salmo salar females and brown trout Salmo trutta males were backcrossed to four male salmon. Their offspring exhibited statistically significantly higher survival than offspring of F1 hybrids of brown trout females backcrossed to three salmon. Some diploid progeny were observed in crosses between Atlantic salmon females and F1 hybrid males, demonstrating that trout×salmon hybrid males can produce reduced gametes. Backcrosses of both hybrid types to brown trout failed. The results as a whole demonstrated that post-mating barriers were asymmetric between Atlantic salmon and brown trout, suggesting that the introgression of brown trout genes into Atlantic salmon gene pools is possible, but not the reverse.