Background. In case of natural hybridisation of fish it is important to determine whether the hybrids attain sexual maturity and whether they can produce generation F2. The hybrids of rudd and carp bream, relatively frequent under natural conditions, have not been studied in the aspect of sexual maturity attainment.Materials and methods. Histological examinations of gonads of 4-5 year old rudd and carp bream hybrids were carried out in experimental environments during the pre-spawning and spawning seasons of the parental species.Results. In development of oocytes the female hybrids of rudd and carp bream reached the stage of migrating nucleus and deterioration of the morphological structure of the nucleus. In case of male hybrids the presence of spermatids was confirmed. The stage of spermatozoa was not observed in case of hybrids of rudd and bream. In case of the control species (rudd) that stage was also not observed. It is possible that the lack of that stage was affected by the parameters of the culture environment. Nevertheless, the sexual products of male hybrids of rudd and bream as well as rudd were deposited.Conclusion. The studies show that the hybrids of rudd and carp bream may reach sexual maturity in the natural environments.

Scardinius erythrophthalmus, Abramis brama, hybrids, attainment of sexual maturity