Gambusia affinis were collected from chetpet fish farm, with the help of fisherman using net and kept in a plastic drum. The
lake water was used for transportation. Fishes were transported quickly to the laboratory. The fishes were acclimatized slowly, in tap water and the experiments were conducted for 48 hours in two replicates. Individual experimental and control tanks were used in the laboratory Gambusia affinis were measured and weighed before and after of the experiment. A control was also maintained separately throughout the experiment conducted in individual fish of five different size groups (3.0, 3.3, 3.6, 3.9, 4.2, and 4.5) against the mosquito larvae of 3rd and 4th instar stage of Culex quinquefasciatus. The larval feeding rate was recorded.