An analysis of 133 populations of Carasiius spp. from wa-ter bodies in Ukraine showed their polyspecific structure: 62 % of individuals of the studied 3453 specimens tur-ned out to be bisexual goldfishes C. auratus, 25 % were unisexual Prissian carps C. gibelio, 6 % accounted for the aboriginal species crucian carp C. carassius, and 6 % were hybrids C. auratus × C. carassius. In this case a clear trend has been revealed towards the formation of homogeneous alternative populations, specifically: either C. auratus, or C. gibelio. Individuals of C. carassius and the hybrids C. auratus × C. carassius typically comprise an admixture in various populations. The cause of the bipolar distribution of individuals of C. auratus and C. gibelio between various water bodies is the instability of mixed populations as far as individuals of C. auratus very quickly replace females of C. gibelio due to their low reproductive potential.