Sex, size and ploidy ratios of Carassius gibelio from poland

Abstract

Unusual tolerance of ecological conditions and an ability of bisexual and unisexual reproduction allows Carassius gibelio (Bloch, 1782) to colonize various habitats from northern Europe to Asia. This non-native species of negligible economic importance has a negative impact on native species and the environment, and is undesirable in any part of Europe. As the reproductive mode is indirectly indicated by sex and ploidy ratios, these two features together with the karyotypes as well as sex-and ploidy-related length-weight relationships were studied in C. gibelio population inhabiting the Siemianówka Reservoir (northern-east Poland). Moreover, we tested the hypothesis that the frequency of triploid or diploid C. gibelio individuals in European populations will be greater than that in East Asia where it is native. The studied population is bisexual, clearly indicated by the presence of females (the sex ratio 3.1:1), represented by triploids and diploids in a 1:1 ratio. The parity of the sex ratio among diploids was noticeable in that most males (78.8%) were diploids but, surprisingly, the rest were triploids. The sex and ploidy ratios indicated both unisexual (via gynogenesis) and bisexual reproduction of C. gibelio. The weight-length relationships were related to sex but not to the ploidy. Compared to native populations, our findings reveal a higher incidence of sexually-reproducing diploids, which may have facilitated their success in invading Europe.