Differentiation of gonad maturation in sibling precocious males of the sea trout (Salmo trutta m. trutta L.) in their first year of life

It is only from microscope-aided analysis of the testes that the class of gonad development can be accurately evaluated and the extent of precocious maturation assessed, particularly in fish maturing for the first time. It is impossible to correctly identify maturing males of the underyearling sea trout on the basis of morphological examination of gonad appearance, abdominal massage to detect spermiation or gonadosomatic index value.