Morphometric differentiation of Labeo catla (Hamilton 1822) (Cyprinidae) in rivers: Possible adaptation to hydrology

Morphological differentiation in the Indian major carp, Labeo catla, in the Ganga and Narmada rivers was studied using image-based morphometric and multivariate analytical techniques. Twenty-three truss-network-based distances connecting 11 anatomical landmarks on the fish were measured from the digital images of the specimens collected from seven stations, four of which were set up along the river Ganga, and the other three stations along the river Narmada. For analysis, five stations were considered, as the samples from the three stations on the River Narmada were pooled and treated as a composite sample (Narmada). The multivariate analysis of variance showed evidence for significant morphometric differences between samples collected from the Ganga and those from the Narmada rivers. The subsequent Linear Discriminant Analysis explained 86% of the variability between the stations by two discriminant functions. This fact suggested the existence of three morphometrically different populations of the species along the Ganga. These populations were predominantly distributed in the middle stretch of the river (Ganga_Middle), the Bhagirathi-Hooghly stretch, and the Padma stretch, which are isolated by a barrage that does not allow free bidirectional movement of fish. The important discriminating morphometric characteristics were traits from the head and caudal region as well as the body depth of fish. The relatively narrower angles of snout profiles and lower body depths of the studied fish in populations from the Padma and Bhagirathi-Hooghly stretches of the River Ganga led to more pointed snouts and slenderer bodies. Morphological differentiation can be used as an environmental predictor that, in turn, would be of use in developing effective management strategies for the fish species of stock management concern.