During the period from October 2002 and November 2003, ovaries of 4–5 year old hybrids obtained as a result of reciprocal hybridization of rudd and carp bream (rudd ♀ x carp bream ♂, carp bream ♀ x rudd ♂) were histologically examined. In both groups of hybrids: rudd ♀ x carp bream ♂ and carp bream ♀ x rudd ♂, females with autumn-spring and spring period of vitellogenesis were found; in the carp bream ♀ x rudd ♂ the majority represented the spring vitellogenesis period (P < 0.05). In both groups of hybrids, during the period preceding reproduction and after reproduction, females showed characteristics to both spawn types: total spawners and batch spawners. Studies show that periods of vitellogenesis: autumn-spring and spring as well as spawn types: total and batch characteristic for carp bream and rudd respectively appear in both genetic lines of their hybrids (rudd ♀ x carp bream ♂ and carp bream ♀ x rudd ♂), and that the frequency of appearance of females with spring vitellogenesis period is higher when carp bream is the maternal species and rudd the paternal one. The results of studies suggest that females representing a different spawn type or vitellogenesis period found in population of crossing fish species can be the hybrids of those species.

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