Anadromous fishes like hilsa shad are found near the delta region of Ganges River which are exotic and carry economic potential. The river offers a tidal environment connecting with marine and freshwater ecosystem providing nutrient-rich seasonal water for their growth and development. The complex migratory pattern of these fishes is a major concern in fisheries research. The present study is based on a large collection of isotopic data from otolith specimens of varying sizes covering population of varying age. Here we examined their stable isotopic signature and relate it with their age and locations in the stream length. Otolith δ¹⁸O showed significant relationships with fish sizes (length and weight) and distance from the river mouth and can provide a new tool to distinguish their habitats. Small size individuals show affinity for freshwater, while bigger individuals originates from Bay area. The ANOVA and discriminant function analysis (DFA) is used to check whether the fish inhabiting upstream and downstream can be categorized by their δ¹⁸O values and to define the composition of the end member. Further, a numerical model of two component mixing is introduced to prescribe the integrated time interval, equated with their size to define specific habitat. The significant variations in otolith δ¹⁸O values are found between upstream and downstream of the Hooghly River, and the DFA showed the overall 81% of individuals were assigned to the upstream or downstream of the Diamond Harbour, while the remaining individuals of 1–2 years age represent mobile population, probably participating in the successful spawning and feeding activities. This method allowed understanding the migration tendency of adult individual (fraction of time spend in the freshwater) and clearly identified the habitat based on isotopic ratios in otolith specimens. This study will serve as template for understanding the aquaculture potential and scientific management policies for hilsa shad in the West Bengal region.

在恒河三角洲地区附近发现了像鲥鱼这样的溯河鱼类，它们具有异国情调并具有经济潜力。河流提供与海洋和淡水生态系统相连的潮汐环境，为它们的生长和发育提供营养丰富的季节性水。这些鱼类复杂的洄游模式是渔业研究的主要关注点。本研究基于从覆盖不同年龄人群的不同大小的耳石标本中收集的大量同位素数据。在这里，我们检查了它们的稳定同位素特征，并将其与它们的年龄和在河流长度中的位置联系起来。耳石 δ ¹⁸O 与鱼的大小（长度和重量）以及与河口的距离显示出显着的关系，可以提供一种新的工具来区分它们的栖息地。体型较小的个体对淡水表现出亲和力，而体型较大的个体则来自湾区。ANOVA 和判别函数分析 (DFA) 用于检查栖息在上游和下游的鱼类是否可以根据它们的 δ ¹⁸ O 值进行分类，并定义末端成员的组成。此外，引入了两个组分混合的数值模型来规定综合时间间隔，等同于它们的大小以定义特定的栖息地。^{耳石 δ 18}的显着变化O 值位于胡格利河上游和下游之间，DFA 显示总体 81% 的个体被分配到钻石港的上游或下游，而其余 1-2 岁的个体代表流动人口，可能参与成功的产卵和喂养活动。这种方法可以了解成年个体的迁移趋势（在淡水中花费的时间比例），并根据耳石标本中的同位素比率清楚地确定栖息地。本研究将作为了解西孟加拉邦鲥鱼水产养殖潜力和科学管理政策的模板。