The morphological, histological and cytogenetic characteristics of goldfish Carassius auratus (L.) x common carp Cyprinus carpio (L.) hybrids

Morphology of hybrids between the goldfish (Carassius auratus) and common carp (Cyprinus carpio) are studied by biometric and meristic methods. Additionally, histological analyses concerning gonads as well as genetic characteristics of chromosomes are performed. Studied hybrids were morphologically very similar to a goldfish but possessed one pair of reduced posterior barbels. Most meristic and biometric indices had intermediate values when compared to parental species. Histological study showed that investigated hybrids produce gonads with germ cells. All studied males had gonads at the same stage of maturity (III stage). By contrast, female gonads were in various stages of development - from sexually immature to post-spawning stage. Karyotype characteristics were assessed in terms of chromosomes number, fundamental arm number and location of nucleolus organizer regions (NOR). The data obtained were compared with baseline karyotypes of species used for hybridization, based on information from the literature. The diploid chromosome number of studied hybrids equaled 2n = 100, NF = 152. Ag-NORs were localized on the short arms of two to three submetacentric chromosomes. Additionally, one to two supernumerary (B) chromosomes were also found, which is a typical phenomenon for interspecific hybrids, especially between cyprinid fish species.