ドジョウの成熟におよぼす水温の影響ならびに周年採卵
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概要
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In order to obtain basic information on the artificial production of fry, the effect of temperature upon egg maturation was examined in the loach, Misgurnus anguillicaudatus. Young females, divided into four groups, were reared for two months in aquaria regulated at 15°C, 20°C, 25°C and 30°C respectively. Rearing experiments were carried out in the summer, from May 20 to July 18, 1975; and in winter, from November 6, 1975 to January 5, 1976. In both summer and winter experiments, the highest gonadosomatic index ratios were in the groups kept at 25°C and 30°C. Loaches of these two temperature groups were injected with human chorionic gonadotropin, 10 IU/g body weight. At least 79% of injected fish spawned within 8 to 14 hours of injection. The average fertilization and hatching rates of eggs in the group kept at 25°C were markedly higher than in those kept at 30°C. On the other hand, in the groups kept at 15°C and 20°C only about 20% or fewer of the injected fish spawned. Other mature females collected from natural streams were aquariumreared at 25°C from June 1975 to March 1976. They spawned successfully after injection with HCG, even in autumn and winter. The out-of-season eggs developed normally and hatched at a rate similar to that for eggs obtained in the spawning season. Furthermore, other adult females, collected from an outdoor wintering pond at 5.3°C on November 23 and kept for 10 days at 25°C, successfully spawned after the injection of HCG, and the eggs hatched normally. Based on these results, we judge that the critical high temperature for egg maturation of this species is about 30°C and the most suitable, about 25°C, and mature females maintain their full maturity almost all through the year.
- 公益社団法人 日本水産学会の論文