The impact of cotton leaching pesticides on the immune system of native fish Oreochromis niloticus and Clarias gariepinus in North Benin

Details

Supervisors

KESTEMONT, Patrick ; IMOROU TOKO, Ibrahim

Faculty

Faculté des sciences

Degree label

Master [120] en biologie des organismes et écologie

Abstract

Cotton culture in Benin plays an important role in the country’s economy, especially in the North. This demanding crop needs phytosanitary treatment inputs, which are often overdosed and can reach surface waters such as reservoirs. In these water reservoirs, several fishing techniques are used, such as floating cages and enclosures (the latter leaving access to the water bottom). Two species, Nile tilapia Oreochromis niloticus and African catfish Clarias gariepinus, are commonly reared in this region’s aquaculture systems. The aim of this research was to evaluate the contamination effect of pesticides on the immune systems of the fish reared in these water reservoirs as well as which fish species is the most impacted by this pollution and finally, to compare and figure out which is the best fishing practice to diminish their exposure to pollutants. Two water reservoirs were selected, Batran, located in an important cotton production area (contaminated site) and Songhaï, located in a low production area (control). Both species were artificially stocked and reared in cages and enclosures installed within two reservoirs during the cotton growing season. Three sampling campaigns took place, one before the phytosanitary treatments began (P1), one during the phytosanitary treatments application (P2) and the last one after the phytosanitary treatments occurred (P3). During each sampling campaign: fish, water and sediment were collected to conduct pesticide dosage and assess several biomarkers of the immune system in both species. Physico-chemical properties of the water reservoirs were also measured during the experiment. Results in Batran, showed that residues of pesticides (i.e. DDT derivatives, chlorpyrifos-ethyl) were found, in higher doses in the African catfish’s flesh. Molecules of pirimiphos-methyl and chlorpyrifos-ethyl were found in African catfish reared in Songhaï. Traces (third of the LOQ value) of acetamiprid were detected in all water and sediment samples from both sites. Dissolved oxygen content seemed to be impaired in the Batran reservoir, suggesting the impact of pesticides on primary production. Pesticide exposure appeared to have immunosuppression and/or immunostimulation effects on several immune system biomarkers. Results showed that African catfish could be more affected than Nile tilapia and that the fish reared in enclosures are more exposed to contamination from pesticides than those reared in cages. Based on these findings, fish reared in the cotton production area (Batran) undergo immunotoxicity processes, especially the African catfish raised in enclosures.