Induction of two types of gynogenetic diploids by hydrostatic pressure shock and verification by genetic marker in ayu.

The induction of gynogenetic diploid by suppression of first cell clevage (abbreviated as the mitotic-G2N for its point of suppressing cell clevage) is considered to be more effective in producing a complete homozygous diploid than the induction of gynogenetic diploid by retention of 2nd meiosis (abbreviated as the meiotic-G2N for its point of retaining 2nd polar body), if we intend to fix and establish a pure line of fish seeds for aquaculture. As it was difficult to induce the mitotic-G2N by cold shock in ayu, the hydrostatic pressure shock which seems to be more promising was applied to find the best condition to suppress the first cell clevage as well as to retain the 2nd polar body of fertilized eggs. Three factors, pressure level, shock duration and starting time of application were examined. The least pressure level and duration required to induce the meiotic-G2N were 500-600 kg/cm2 for 6min and 600-700 kg/cm2 for 6min to induce the mitotic-G2N. The induction of these two types of gynogenetic diploids were verified by an isozyme genetic marker, i.e. Gpi-1 which showed almost 100% heterozygosity in the meiotic-G2N, and complete homozygosity in the mitotic-G2N.