Oreochromis niloticus (Nile tilapia) is one of the most produced fish for human consumption globally; however, these fish are susceptible to exposure to toxic chemicals in the water. Pyriproxyfen is a pesticide widely used to control mosquitoes in drinking water supplies and pests in crops. The present study aimed to examine pyriproxyfen's effects on fish O. niloticus fingerlings exposed using an acute 96 h and subchronic tests for 28 days. The lethal concentration LC50-96 h for O. niloticus was 2.77 mg L-1, no observed effect concentration (NOEC), and the lowest observed effect concentration (LOEC) was 1.0 and 2.5 mg L-1, respectively. The hepatic catalase activity was significantly changed after exposure to pyriproxyfen above 0.4 mg L-1. Pyriproxyfen also induced histopathological lesions in the hepatic tissue at 28 days in a dose-dependent pattern at concentrations above 0.4 mg L-1. Pyriproxyfen above 1.2 mg L-1 reduced the locomotor behavior, distance traveled inside the tank, mean speed, and angular variation. This pesticide also decreased weight gain, food conversion, and specific growth rate at concentrations above 1.2 mg L-1. In conclusion, exposure to pyriproxyfen in water from 0.4 mg L-1 may impair O. niloticus development; consequently, pyriproxyfen may affect this fish's production and quality at higher concentrations than commonly used in water (0.01 mg L-1).