The common Japanese conger, Conger myriaster, is one of the most important fisheries resources in Japan. However, the catch of the common Japanese conger has decreased by nearly 80% over the past 25 years, and the early establishment of aquaculture and seedling production technology is required. In order to conduct the first stage of seedling production, egg collection, it is necessary to understand the maturation mechanism of the common Japanese conger, but there are still many unknowns, both in the wild and in captivity. To date, there have been no comparative studies of the interannual changes in the common Japanese conger gonads under different rearing conditions. In this study, we investigated the effects of different rearing water temperatures on the annual changes in the gonadal development. The fish were reared in an environment where the annual water temperature varied from 8.0 to 24.4°C (16.1 ± 5.0°C) and 8.5 to 19.5°C (13.9 ± 2.9°C) were designated as group 1 and 2, respectively. The GSI and egg diameter of females in group 1 increased until July, when the water temperature did not exceed 20°C. From August onward, the GSI and egg diameter decreased rapidly when the water temperature exceeded 20°C. In group 2, the GSI and egg diameter increased in August, when the water temperature did not exceed 20°C. In group 2, GSI and egg diameter increased in August and were significantly higher than in group 1 in September and October. The GSI of males was higher in the group 1 at most of the time except for the period of advanced regression. These results indicate that low water temperatures of less than 20°C in rearing condition lead to more advanced maturity in both males and females. However, water temperatures not exceeding 20°C per year were thought to suppress ovarian regression and cause large individual variation in maturity.

Departmental Bulletin Paper

application/pdf