author(s)
Rinchen Nopu Bhutia, Sri Hari M, Nagesh Talagunda Srinivasan, Geetanjali Deshmukhe, Karankumar Ramteke, Shashi Bhushan and Asha Taterao Landge

abstract
Ailia coila (Hamilton, 1822) commonly called as Gangetic ailia is a “Near Threatened” species in the IUCN Red list. Total of 421 samples were taken from the Ganga (Samudragarh and Farakka) and Brahmaputra (Dhubri and Guwahati) river systems for the present study. The landmark-based truss network system was employed to delineate the stock of this species. The truss network was constructed by using 12 landmarks and 25 truss distances were extracted. Factor analysis using varimax rotation for differentiating the population explained 74.53% of the total variation in the data from first three factors; with first, second and third factors contributing 56.32%, 10.83%, 7.38% of the variations respectively. The morphological difference between the stocks of this species was related to oblique depth measurement on the dorsal and anal fin, and also on the caudal peduncle region. Discriminant function analysis was employed to reveal the percentage correctly classified individuals on the respective locations. Overall classification rate is found to be good around 97.85%. The percentage correctly classified was highest in Samudragarh (100%) which was followed by Farakka, Dhubri and Guwahati. The results from this present study reveals the existence of difference stock in Ganga and Brahmaputra and it forms a baseline study for the stock-specific management measures. Further, genetic population structure of this species should be studied using molecular markers to validate the results.