Early gametogenesis of the Volkhov whitefi sh, Coregonus lavaretus baeri

The fi rst detailed examination of the gonadal development of Volkhov whitefi sh juveniles was performed. Morphology and sequence of germ cells and gonad development are presented. Thirty days after hatching in the gonad anlagen, primordial germ cells began to divide. Sex differentiation occurred 82 days after hatching. Gonia in ovaries proliferated rapidly, some of them entered meiotic prophase developing into oocytes. In two weeks, the developing oocytes had reached the ‘early perinucleolus stage’ and began the cytoplasmatical growth. At the same time, in ovaries of some females, cysts with male germ cells appeared. Ten days later, all whitefi sh females had hermaphroditic features. In male gonads few germ cells were dispersed singly amongst stromal tissue. The reason for the mass hermaphroditism among Volkhov whitefi sh females may lie in the environmental circumstances such as high temperature during the study period, or the specifi city of the early gametogenesis in this whitefi sh species.