|
This study was carried out to investigate the appearance time of the second polar body for producing Gynogenesis or Triploid which could be obtained by arresting the second polar body by cold shock, and then blastoderm was used to measure fertility that revealed the nature of oogenesis, the effects of water temperature on fertility, hatchability, abnormality, viability and growth rate, and the water temperature and the breeding methods to prevent early death of larvae in Korean loach(Misgurnus anguillicaudatus) ; the results obtained in this study were summarized as follows. The second polar body was observed ont he surface of plasma disc close to micropyle within 10~40 min after fertilization at 29^{circ}C. Artificial inseminatin had to be done immediately after the egg spawning because the spermatozoa of loach their mobility within 2 minutes when they were exposed to water. The amount of time needed to reach at blastoderm stage was 12 hours if fertilized eggs were incubated at 16^{circ}C, 8 hours at 19^{circ}C, 6 hours at 21^{circ}C, 5 hours at 23^{circ}C, 4 hours at 26^{circ}C and 3 hours 30 min at 29^{circ}C showing the shorter time for development of eggs at higher temperature. Fertilization rates in water temperatures of 19^{circ}C, 21^{circ}C, 23^{circ}C, and 26^{circ}C were higher than those of water temperatures, 16^{circ}C and 29^{circ}C. Water temperatures at 19^{circ}C, 21^{circ}C and 23^{circ}C showed higher hatching rates that those of 16^{circ}C 26^{circ}C, and 29^{circ}C, while abnormal rates in 16^{circ}C, 19^{circ}C, 21^{circ}C and 23^{circ}C were lower than that of 26^{circ}C and 29^{circ}C. Water temperatures at 16^{circ}C, 19^{circ}C, 21^{circ}C, 23^{circ}C and 26^{circ}C respectively, were more different than 29^{circ}C in survival rates. The embryos were hatched at 72 hours after fertilization in 16^{circ}C water temperature, 48 hours in 19^{circ}C, 40 hours in 21^{circ}C, 32 hours in 23^{circ}C, 25 hours in 26^{circ}C, and 16 hours in 29^{circ}C. Within three days after hatched out, the larvage grew 3mm in total length, the yolk granules were entirely consumed and the head and the trunk became thicker. Within 45 days after hatched out, the larva grew 25mm at 29^{circ}C, 21mm at 26^{circ}C, 16mm at 23^{circ}C, 15mm at 21^{circ}C, 12mm at 16^{circ}C in a 30 litreglass aquarium.
|