中国东南沿海日本鳗鲡幼体的日龄及其孵化时间

Daily age and hatching time of Japanese eel elvers from southeast coastal estuaries of China

测定了2008年1—3月采自中国广东至江苏沿海9个河口的538尾线鳗的体长和矢耳石长轴半径,分析了其中107尾线鳗矢耳石的日龄结构。结果表明,线鳗的体长在47.40～62.34 mm,平均(54.77±2.21)mm,各采样点的平均体长存在极显著差异(ANOVA,P<0.001)。矢耳石长轴半径为133.22～175.95μm,平均(154.55±9.09)μm,各采样点之间无显著差异(P>0.05)。线鳗的日龄为124～158 d,平均(135.78±6.84)d,呈现出从南到北逐渐增加的趋势,其中最北部的大丰较最南部的新会大了15.9 d。根据日龄和采集时间推断,这些标本的孵化时间在9月6日—10月20日,主要集中在10月中旬,85.98%个体符合孵化时间的新月假设。分析表明,孵化较早的个体到达河口的时间也较早,生长速度快的个体也比生长慢的个体到达河口的时间要早。

The Japanese eel,Anguilla japonica,is one of the most important cultured species,widely distributed in rivers of the northeastern Asian countries＇ Taiwan,China,Korea and Japan.The spawning grounds were recently discovered in the North Equatorial Current west of the Mariana Islands,15°N,140°E.From January to March 2008,there were 538 Japanese eel elvers collected from nine estuaries along Guangdong Province to Jiangsu Province which were measured on total length and long radius of sagitta otolith.Furthermore,observations were based on growth increments in sagittal otoliths of elvers collected at 9 sites.These results indicated that total length of elvers were 47.40 mm to 62.43 mm,the average value was（54.77±2.21） mm and the mean total length of each site was significantly different（ANOVA,P0.001）.As for long radius of sagitta otolith,it was from 133.22 μm to 175.95 μm,the average value was（154.55±9.09） μm and there was no significant difference among each site（ANOVA,P0.05）.Daily age of elvers ranged from 124 d to 158 d and the average value was（135.78±6.84） d,indicating that migration of eel larvae from their oceanic spawning ground to the estuary requires 4 to 5 months.An obvious trend of daily age was increasing from southern to northern areas and the maximum difference was 15.9 d.Elver hatching dates,back-calculated from estimated daily ages,indicated that the spawning season lasted 2 months（from Sep.6 to Oct.20）,mainly concentrated in middle of October and approximately 85.98% samples accorded with New Moon Hypothesis.Finally,the inverse correlation between daily age and mean daily growth rates of fish length and otolith radius indicated that the time taken on migration from oceanic spawning ground to the estuary was shorter for fast-growing larvae than fast-growing elvers which arrived at the estuary earlier than slow-growing ones.