The Hilsa, Tenualosa ilisha, commands a very high value as food fish. The present study was carried out to understand the breeding phenology of T. ilisha in relation to climatic variables. Monthly fish samples were collected from two landing centres, namely, Uzanbazar (Guwahati) and Shri Ramghat, Dhubri, of River Brahmaputra during May 2018 to April 2019. The assessment of gonadosomatic index (GSI) of T. ilisha revealed higher GSI values during October to February, and showed temporal variations with respect to sex. In males, highest GSI value was observed in the month January followed by February, whereas in females, GSI value was found to be highest in November followed by October. GSI (pooled) value was negatively correlated with air temperature, indicating vulnerability of the species to climate change. The highest percentage of mature males was observed during October–February, and mature females during October–December. The length at first maturity was recorded to be 290 mm for female(s) and 259 mm for male(s). The absolute fecundity ranged from 103,164 to 583,456 ova for fishes in the size range of 229–403 mm, with an average of 250,532 ova per female. Relative fecundity was found to range from 306 to 1096 ova per gram body weight, with an average of 791 ova per gram body weight. The diameter of ova of the studied fishes ranged from 414.6 to 738.2 µm, with a mean value of 546.73 ± 7.18 µm. The percentage frequency distribution of mature ova shows a distinct single peak or mode. Sex ratio (male: female) was found to be 1:0.87, indicating dominance of males over females. The chi-square test on observed sex ratio against the hypothetical ratio of 1:1 did not reveal a significant difference (p > 0.05). The findings of the present study can provide impetus toward successful management of this highly prized, transboundary, and migratory resource of River Brahmaputra, in the context of changing climate.

中文翻译：

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了解与印度布拉马普特拉河气候变量相关的溯河鱼类 Tenualosa ilisha（汉密尔顿，1822 年）的繁殖物候

希尔萨，Tenualosa 伊利沙, 作为食用鱼具有很高的价值。进行本研究以了解育种物候学T.伊丽莎关于气候变量。2018 年 5 月至 2019 年 4 月期间，每月从雅鲁藏布江的 Uzanbazar (Guwahati) 和 Shri Ramghat, Dhubri 这两个着陆中心采集鱼类样本。T.伊丽莎在 10 月至 2 月期间显示出较高的 GSI 值，并显示出与性别有关的时间变化。在男性中，GSI 值最高出现在 1 月，随后是 2 月，而在女性中，GSI 值最高出现在 11 月，随后是 10 月。GSI（汇总）值与气温呈负相关，表明该物种对气候变化的脆弱性。在 10 月至 2 月观察到成年雄性比例最高，在 10 月至 12 月观察到成年雌性比例最高。据记录，雌性初熟时的身长为 290 毫米，雄性为 259 毫米。对于尺寸范围为 229-403 毫米的鱼类，绝对繁殖力从 103,164 到 583,456 个卵子不等，平均每只雌性 250,532 个卵子。发现相对繁殖力范围为每克体重 306 到 1096 个卵子，每克体重平均含有 791 个卵子。所研究鱼类的卵子直径范围为 414.6 至 738.2 µm，平均值为 546.73 ± 7.18 µm。成熟卵子的百分比频率分布显示出明显的单峰或模式。性别比例（男性：女性）被发现为 1:0.87，表明男性对女性的优势。观察到的性别比例与假设比例 1:1 的卡方检验未显示出显着差异（p> 0.05）。本研究的结果可以为在气候变化的背景下成功管理雅鲁藏布江这一珍贵的跨界迁徙资源提供动力。