Spatial variation in the otolith shape of Asian sheat catfish, Wallago attu (Bloch & Schneider, 1801) populations from five Indian rivers

The population of Wallago attu (Bloch & Schneider, 1801) has declined worldwide including in the rivers of India and has been declared ‘Vulnerable’ by the International Union for Conservation of Nature. The restoration and conservation of fishes is heavily dependent on their population status in their natural habitats. Therefore, otolith shape was used to study the stock structure of W. attu from rivers Ganga, Gomti and Yamuna in Northern India, river Hooghly in Eastern and Pampa in Southern part of India. Shape indices of the asteriscus otoliths and elliptical Fourier analysis of the contour shapes was investigated using univariate and multivariate statistical techniques. The otolith descriptors (otolith length, breadth, area and perimeter) and four shape indices (length-breath ratio, form factor, circularity and ellipticity) of the otoliths were different (ANOVA, p<0.05) between the fish of five sampled rivers. Principal component analysis of normalized elliptical Fourier descriptors (NEFDs) of the contour shape accounted for 89.55% of the total variance. Discriminant function analysis on the basis of NEFDs resulted in 100% classification rate with no intermixing between the fish of different rivers and depicted the presence of different stocks of W. attu in a scatter plot of DF-I against DF-II. These variations in the otolith shape in the current study might be due to the restricted movement of fish because of geographical isolation and different environmental conditions in different rivers due to changes in habitat, or both. The current study would be helpful in developing effective strategies for stock management of this species.