State of Gonads of Underyearlings of Brown Trout Salmo trutta (Salmonidae) from the Alatsoya River (Karelia)

Signs of early maturation have been revealed in 50% of underyearling males of brown trout from the Alatsoya River in Karelia: spermatocytes of the first- and second-orders and spermatids were observed in their testes. Precociously mature males began to be formed as early as the first summer of their life. Signs of early maturation have not been observed in females at age 0+. Gonads contained germ cells of opposite sexes in a very small number of individuals.