Induction of Gynogenetic Diploids and Cytological Studies in Honmoroko Gnathopogon caurulescens

Abstract

The production of gynogenetic diploids of honmoroko by cold-shock treatment with UV-ir-radiated nigorobuna sperm was examined. 2000 ?? 10000ergs/mm² was the optimum UV dose to genetically inactivate nigorobuna sperm which was diluted 100 times by physiological saline solution. The highest yield of gynogenetic diploids was produced after a 40 min duration of cold-shock (CS: 0 ?? 0.3°C) treatment. When the eggs were incubated at 15.0, 20.0, and 25.4°C, the best times to start CS treatment were 12, 7, and 4.5 min after insemination, respectively. The hatching from the eggs CS treated (for a 40 min duration) between just after insemination and after 90 min peaked at 7, 12, 40, 70, and 90 min and showed periodical fluctuations. The yield of normal fry showed higher values when the CS treatment was started 3 ?? 7 min after insemination, but there were low rates of normal fry hatched at times between 10 and 90 min. The egg showed the metaphase of the second maturation division at the time of insemination, and advanced to the anaphase by 5 to 7 min after insemination. The extrusion of the second polar body was observed 10 min after in-semination. The metaphase of the first cleavage and the prophase of the second cleavage were seen 40 and 60 min after insemination, respectively. These results suggest that CS treatment (0°C, for 40 min 3 ?? 7 min after insemination) is a practical method for the induction of gynogenetic di-ploids in honmoroko, caused by prevention of the formation of the second polar body.