Hatakeyama Rui, Akiyama Nobuhiko
Ocean Research Institute, University of Tokyo, Tokyo, Japan.
Zoolog Sci. 2007 Jun;24(6):614-22. doi: 10.2108/zsj.24.614.
From June 2000 to September 2001, we investigated the presence of eggs spawned in Margaritifera laevis and the seasonal changes in the gonads of Tanakia tanago. Eggs were observed from mid-March to mid-September. In females with a shrunken ovipositor, as the GSI gradually increased, most ovaries were in the prespawning phase (Oct-Mar). As the GSI increased further, most ovaries were in the early spawning phase (Mar-Jun). As the GSI gradually deceased, ovaries in the late spawning phase appeared (Jun-Sep). When the GSI was very low, most ovaries were in the postspawning phase (Sep-Oct). In males, when the GSI was low, most testes were in the early prespawning phase from Oct-Dec. As the GSI gradually increased, most testes were in the late prespawning phase (Dec-Jan). As the GSI increased further, testes were in the early spawning phase (Jan-Jun). As the GSI gradually decreased, amost testes were in the late spawning phase (Jun-Sep). When the GSI was very low, most testes were in the postspawning phase (Sep-Oct). These results indicate that T. tanago has a distinct annual reproductive cycle and is a spring-autumn spawner. Based on the relationship between reproductive activity and environmental factors, the spawning season of T. tanago appears to be initiated by increasing temperature and / or longer days in spring and to be terminated by shorter days in autumn.
2000年6月至2001年9月，我们调查了珍珠蚌（Margaritifera laevis）中产出的卵以及日本田奈鱼（Tanakia tanago）性腺的季节性变化。3月中旬至9月中旬观察到了卵。在产卵器萎缩的雌鱼中，随着性腺成熟系数（GSI）逐渐增加，大多数卵巢处于产卵前阶段（10月至次年3月）。随着GSI进一步增加，大多数卵巢进入产卵早期阶段（3月至6月）。随着GSI逐渐下降，出现了处于产卵后期阶段的卵巢（6月至9月）。当GSI非常低时，大多数卵巢处于产后阶段（9月至10月）。在雄鱼中，当GSI较低时，大多数精巢在10月至12月处于产卵前早期阶段。随着GSI逐渐增加，大多数精巢处于产卵前后期阶段（12月至1月）。随着GSI进一步增加，精巢处于产卵早期阶段（1月至6月）。随着GSI逐渐下降，大多数精巢处于产卵后期阶段（6月至9月）。当GSI非常低时，大多数精巢处于产后阶段（9月至10月）。这些结果表明，日本田奈鱼有明显的年度繁殖周期，是春秋季产卵鱼类。根据繁殖活动与环境因素之间的关系，日本田奈鱼的产卵季节似乎是由春季温度升高和/或白昼变长引发，并在秋季因白昼变短而结束。
