Study of feed intake rate as a physiological biomarker in Nile Tilapia, Oreochromis niloticus (Linnaeus 1758) under Chlorpyrifos and Cypermethrin exposure.

Chlorpyrifos and cypermethrin are the two most extensively applied insecticides in agricultural areas across the world and are found to contaminate adjacent water bodies, posing risks to non-target aquatic organisms, including fish. Aquaculture is primarily concerned with the feeding and growth of fish. This study evaluated the effects of sub-lethal concentrations of chlorpyrifos and cypermethrin on the physiological biomarker 'feed intake rate' of Oreochromis niloticus through 96 h static renewal bioassays. The fish were fed a formulated diet containing 30 % crude protein at 5 % of their body weight per day. The feed intake rate calculation was based on the outcome of 6 h feeding of fish carried out in glass aquariums. Uneaten diets (leftovers) were carefully collected and dried, and the weight of the uneaten diets was subtracted from the total amount of dry feed delivered to determine the actual feed intake rate. In the present study, the actual feed intake rates in O. niloticus exposed to chlorpyrifos and cypermethrin varied from 3.06 ± 0.02 to 3.92 ± 0.02 g/100 g BW/d and from 3.32 ± 0.02 to 4.02 ± 0.01 g/100 g BW/d, respectively. Feeding rates and growth of O. niloticus decreased in all sub-lethal concentrations of both test pesticides when compared to the control. Even at a sub-lethal concentration of 5 μg/L chlorpyrifos and 0.5 μg/L cypermethrin, O. niloticus lost its appetite. It can be concluded that chlorpyrifos and cypermethrin even in low concentrations (μg/L) in aquatic media can affect the feed intake rate and growth in fish.