PRODUCTION OF CLONAL AYU BY CHROMOSOME MANIPULATION AND CONFIRMATION BY ISOZYME MARKER AND TISSUE GRAFTING

We attempted to produce clonal fish by chromosome manipulation in ayu Plecoglossus altivelis. To induce mitotic gynogenesis diploids (mitotic-G2N as complete homozygous individuals), the eggs were inseminated with UV-irradiated sperm of normal diploid and were treated with a hydrostatic pressure of 650 kg/cm2 at 80 min after insemination and just before the first cell cleavage. The production of mitotic-G2N was confirmed by isozyme markers. The mitotic-G2N produced from the female parents which were heterozygous at Gpi-1, Me-1 and Pgm loci showed segregation into two homozygous types at those loci, and they were female in all individuals. To produce clonal fish, the eggs of mitotic-G2N were inseminated with the UV-irradiated sperm of normal diploid. The diploidization was achieved by retaining the second polar body with cold shock. Two families of clonal fish were produced and designated as clone-1 and clone-2. The clonal fish examined were all homozygous types in which their genotypes were the same as their mothers in each of clonal fish. The graft-tissue (a piece of operculum) transplanted into their intraclonal sibling hosts survived and was accepted. On the other hand, the graft-tissue transplanted into the different clonal hosts was rejected in both clones. These results suggest that intraclonal siblings possessed completely identical histocompatibility genes.