LAUSR

It has been hypothesized that geographical isolation between river ecosystems often resulted in phenotypic variation and ultimately change in the population structure of aquatic species. To test the hypothesis, 471 individuals of Tor Mahseer, Tor tor, were collected across its distribution range from 18 locations on 10 Indian Rivers covering the Ganges, Narmada, and Godavari River basins to assess the population‐level inter‐ and intra‐basin shape variation through landmark‐based “geometric morphometrics.” Overall, multivariate analysis of variance (MANOVA) showed significant differences (F = 3.33, p < .001) in shape across wild populations. The Mahalanobis and Procrustes distances extracted from canonical variate analysis (CVA) were found to be significant (p < .001) between basins and nonsignificant (p > .001) within basin except Banas and Kali Sindh Rivers in the Ganges River basin. The results indicated that Tor Mahseer in Indian Rivers were represented by four heterogeneous phenotypic stocks (1: the Ganges River basin except Banas and Kali Sindh River; 2: the Banas and Kali Sindh River; 3: the Narmada River basin, and 4: the Godavari River basin) based on their shape. The wireframes depicted variation mainly in the head region, body depth, and the caudal peduncle area between four phenotypic stocks. The population‐level shape variation between the basins might be due to geographical isolation between the basins and within the Ganges basin because of river fragmentation due to habitat alteration, which restricts the movement of fishes. This study is useful for resolving the “phenotypic stock” complexity in order to develop a suitable stock management plan with the aim of conserving and restoring populations of Tor Mahseer in Indian Rivers.