Since 1992, cotton has been Benin's top agricultural sector, constituting over 35% of its exports. Production focuses on the northern region, primarily in the Borgou and Alibori departments, contributing around 70% of the nation's output. However, cotton farming faces challenges from pests, leading to extensive pesticide use. In 2015, Benin spent $6.8 million on pesticides, half of which were highly hazardous. Unfortunately, only 1% effectively targets pests, while the remaining 99% pollute ecosystems, particularly aquatic ones. This pollution affects water bodies crucial for fish, supplying over 60% of the region's fresh fish, including Oreochromis niloticus. Consequently, pesticide contamination poses environmental and health risks. To assess this, a study was conducted to examined the impacts of cotton field effluents on Oreochromis niloticus in Batran water reservoir on the immune, haematological, and growth responses during the dry season. The 56-day in-situ experiment, approved by the University of Parakou's Faculty of Agronomy, adhered to animal care guidelines using a 2 × 1 experimental design with a pen culture system and two environments: the Batran water reservoir (polluted environment) and a concrete tank at the Aquaculture Research Station (SRIA) of the University of Parakou (reference environment).