浜名湖におけるトビヌメリの生殖年周リズム
1989 年 55 巻 4 号 p. 591-599
詳細
1989 年 55 巻 4 号 p. 591-599
The annual reporductive rhythm of the tobinumeri-dragonet Repomucenus beniteguri was investigated for two consectuive years. In females, mean gonadosomatic index (GSI) peaked in late May (3.93%, 1986; 2.86%, 1987), and decreased to the lowest value during the summer (0.81%, 1986; 0.43%, 1987). It increased again in September, peaked in October (5.45%, 1986; 5.91%, 1987), and declined to 1.06% during the winter. About 40% of the females were ovulated in May, whereas all the females caught in October were ovulated. Ovaries were either regressed or immature in August. Changes in the GSI of males were similar to those of females, although the maximum level (0.29%) in males was very low.
In the females, plasma estradio-17 β (E2) levels exhibited seasonal changes in relation to GSI changes. Peak values of E2 were observed in May (0.79ng/ml) and October (0.78ng/ml). The lowest levels (0.17ng/ml) were detected in August. Plasma testosterone levels also increased in both spawning seasons, but the levels were very low ( ?? 0.31ng/ml). In males, plasma 11-ketotestosterone levels were detectable only in May (0.50ng/ml) and October (0.15ng/ml). Changes in plasma testosterone levels did not correlate with GSI changes in the males.
