Behavior of spindle and chromosomes in early development of gynogenetic amago salmon eggs was examined for explication of basic cytological mechanisms to induce gynogenetic diploid using genetically inactivated rainbow trout sperm by UV-irradiation and with heat shock treatment (0°C for 20 min) for retention of second polar body. The heat shock treatment that started 30 minutes after insemination of amago salmon eggs incubated at 12.0°C was the optimum condition to induce meiotic gynogenetic diploids compared with other conditions of treatment. At 30 minutes, the eggs were in late anaphase of meiosis II. The percentage of eggs that became diploid larvae when treatment started at 5 to 30 minutes after insemination varied little. When treatment started at anaphase, the survival rate was greater than when treatment started at metaphase. It seems that physical damage to the eggs caused by heat is less at anaphase. The second polar body was retained in fewer eggs when heat treatment started later, in the range of 35 to 60 minutes after insemination. Cytokinesis may have prevented such retention more than the increased distance between chromosomes.