Impaired gonadal development in the sea trout (Salmo trutta) × Atlantic salmon (Salmo salar) F1 hybrid females

Despite large karyotype differences between parental species, the hybrid progeny of the sea trout (Salmo trutta) females (2n = 80, FN = 100) and the Atlantic salmon (Salmo salar) males (2n = 58, FN = 74) may be viable and even fertile. As hybrids would pose threat to natural populations of parental species through backcrossing, gonadal development in the sea trout × Atlantic salmon hybrids has been studied in the present work. Moreover, cytogenetic investigation was performed to identify any changes in the number and structure of chromosomes that may affect gonadal differentiation and gamete production in the hybrid progeny. Eight males, two intersex individuals and one female were described among the two-year-old hybrids. Some of the hybrid males were already spermiating during the study. Predominance of the testicular component in the gonads was observed in both intersex individuals. Prevalence of males and the presence of intersex individuals together with only one female may suggest disturbances in the gonadal development only in females. Homogeneity of the chromosome number (69) and the chromosome arm number (87) in the hybrid individuals analyzed in this study suggests that unpaired chromosomes disturbed the development of ovaries but not testes.