REPRODUCTIVE ABILITY OF SECOND GENERATION KOI X GOLDFISH HYBRID MALES AND RESULTS OF THEIR CROSSES WITH KOI FEMALES
Previous studies have shown that F1 hybrid females between ornamental koi carp (Cyprinus carpio) and goldfish (Carassius auratus) produce diploid eggs due to a transformation of meiosis. Hybrid F1 males are typically sterile, but a single fertile male, which produced diploid spermatozoa, was found. When crossed with koi females, this male produced triploid hybrids. Also, the F1 male was crossed with F1 hybrid females for the production of F2 hybrids. F2 progenies consisted mostly of diploids. Analysis of microsatellite DNA markers showed that diploid males repeated the genotype of the parent F1 male while diploid females repeated the genotypes of the parent F1 females. On this basis, it was suggested that diploid males and females in F2 resulted respectively from spontaneous androgenesis and spontaneous gynogenesis.
The purpose of the present study was to investigate the reproductive ability of diploid F2 males. Thirty three from 185 (18%) investigated 2-year-old F2 males released sperm. Flow cytometric analysis showed that spermatozoa produced by F2 males were diploid. Three F2 hybrid males were crossed with koi females. In each cross, a mixture of eggs from several koi females was fertilized with sperm from individual hybrid males. Results of flow cytometric analysis of juveniles from obtained progenies are presented in Table 1. Only triploids were found in progenies from crosses of F2 hybrid males with koi females, while fish in the control (koi x koi) were diploid.
The results of the present study show that the reproductive ability of F2 males was similar to the reproductive ability demonstrated earlier by the fertile F1 male. Like the F1 male, F2 males produced diploid spermatozoa and generated only triploids when crossed with koi females. It is remarkable that almost 20% of F2 males were able to produce sperm. This increase in reproductive capacity of F2 males as compared with F1 males could be predicted since based on previous data all of the F2 males inherited the genotype of the fertile F1 male.