Guo Hong-Yi, Zheng Yi, Tang Wen-Qiao, Shen Hao, Wei Kai, Xie Zheng-Li, Tsukamoto Katsumi
Laboratory of Ichthyolology, Shanghai Fisheries University, Shanghai 200090, China.
Dongwuxue Yanjiu. 2011 Aug;32(4):442-50. doi: 10.3724/SP.J.1141.2011.04442.
The Yangtze River estuary is the main production area of Anguilla japonica in China, as well as the only existing fishery area for adult eels. Japanese eels are distributed in the main rivers and many tributaries from the Yangtze River estuary to the upper Jinsha River, which extend to nearly 3 000 km. However, their migration behaviors remain relatively unknown. We analyzed the biological characteristics of 153 specimens of silver eels collected from the Jingjiang section of Yangtze River (31(o)30'N, 120(o)42'E) between September and November, 2008, and tested the sagittal Sr/Ca ratios of 27 specimens. Among the 153 specimens examined, 85 were female and 68 were male, which translated to a female-male ratio of 1 : 0.8. The ages of the female specimens ranged from 3 to 7 a (average 5.52) with an average total length (TL) of (669 ± 80) mm, average body weight (BW) of (555 ± 229)g, average condition factor of 1.77 ± 0.22, and average gonad somatic index (GSI) of 1.32 ± 0.31. The ages of the males ranged from 3 to 5 a (average:4.38) with an average TL of (518 ± 51) mm, average BW of (234 ± 76) g, average condition factor of 1.62 ± 0.18, and average GSI of 0.21 ± 0.11. All biological parameters of females were significantly larger than those of the male specimens (P<0.05). According to the average Sr/Ca ratio (7.99 ± 1.05) × 10(-3) of the elver mark of sagitta, 17 individuals (62.96%) were river eels and 10 individuals (37.04%) were estuarine eels. Of 16 females, 13 individuals (81.25%) were river eels and 3 were estuarine eels, while of 11 males, 36.36% were river eels and 63.64% were estuarine eels. The analysis on Sr/Ca ratios for every growth layer group (GLG) indicated there were no significant differences between second-age males and females. However, significant differences were observed between the third-age, fourth-age, and migration-age male and female specimens. This was likely related to the fact that second-age eels of both sexes stay in the same inhabitation waters; however, as they grow older, they move to different areas.
长江口是中国日本鳗鲡的主要产区，也是成年鳗鱼现存的唯一渔业区域。日本鳗鲡分布于从长江口到金沙江上游的主要河流及众多支流，其分布范围延伸至近3000公里。然而，它们的洄游行为仍相对不为人知。我们分析了2008年9月至11月间从长江靖江段（北纬31°30′，东经120°42′）采集的153尾银鳗的生物学特征，并检测了27尾样本矢耳石的锶钙比。在所检查的153尾样本中，雌性85尾，雄性68尾，雌雄比例为1:0.8。雌性样本年龄范围为3至7龄（平均5.52龄），平均全长（TL）为(669±80)毫米，平均体重（BW）为(555±229)克，平均肥满度为1.77±0.22，平均性腺成熟系数（GSI）为1.32±0.31。雄性样本年龄范围为3至5龄（平均4.38龄），平均TL为(518±51)毫米，平均BW为(234±76)克，平均肥满度为1.62±0.18，平均GSI为0.21±0.11。雌性的所有生物学参数均显著大于雄性样本（P<0.05）。根据矢耳石鳗线平均锶钙比(7.99±1.05)×10⁻³，17尾个体（62.96%）为河鳗，10尾个体（37.04%）为河口鳗。在16尾雌性中，13尾个体（81.25%）为河鳗，3尾为河口鳗；而在11尾雄性中，36.36%为河鳗，63.64%为河口鳗。对每个生长层组（GLG）的锶钙比分析表明，2龄雄性和雌性之间无显著差异。然而，在3龄、4龄和洄游期的雄性和雌性样本之间观察到显著差异。这可能与两性2龄鳗鱼生活在相同栖息水域这一事实有关；然而，随着它们年龄增长，会迁移到不同区域。
