ドジョウの放卵数,卵巣卵数および卵径分布

抄録

In order to obtain basic information for the artificial fry production in the loach, Misgurnus anguillicaudatus, a number of ovarian eggs and artificially spawned eggs by hormone injection and egg diameter were examined in adult females of various sizes and ages. Females of three and more years of age showed 100 per cent spawning against the total injected females, although two-year females comprised 84.8 per cent. About 56 per cent ripe eggs against the total ovarian eggs were spawned at a time. Number of ovarian eggs and spawning eggs increases propor-tionally with the body weight of adult females. In females larger than 15.2g in body weight, number of spawning eggs per unit body weight and gonadosomatic index also increase proportionally with the body weight, but in females smaller than 15.2g such interrelationship is not observed. The size composition in ovarian eggs displays characteristic features of the type of asynchronism, that is, the ovary in the full stage contains ovarian eggs of various sizes. Based on these results, adult females larger than ablout 15g may be more fruitul for artificial egg taking than the smaller females and the loaches may spawn several times within a spawning season.