Invasion, Biology and impact of feral population of Nile tilapia (Oreochromis niloticus Linnaeus, 1757) in the Ganga River (India).

In this study, we aimed to determine the dispersion area and population characteristic of Oreochromis niloticus (i.e., the abundance, length-weight, food and feeding, gastro somatic index (GaSi), sex ratio, gonado somatic index (GSI) and fecundity) which has formed a feral population in the Ganga River, the largest one in the country. Water parameters were studied in relation to Oreochromis niloticus between years 2008 and 2012. Abundance of O. niloticus in the fishery of the river was observed. Condition factor for feral O.niloticus was calculated which ranged from 2.07-3.64 during successive years. The gut content analysis revealed the presence of over 80% bacillariophyta and cyanophyta comprising of the phytoplankton; crustaceans and rotifera were the primary groups of zooplankton. Calculated GaSi ranged from 7.05 to 11.41 at different sampling sites. Sex ratio indicated the presence of more females than males, indicating an increased propagule pressurs. GSI was ranged from 0.27-3.90 in different catches. High fecundity was observed at locations where the fish had high abundance, indicating an increased spawning potential of the feral fish. The change in dynamics of the fishery was a consequence of increased yield of O.niloticus in the river attracting attention to conserve native germplasm facing threats of shifting from their natural habitats.