Agricultural Pesticide-Induced Physiological Stresses in Freshwater Fishes of Bangladesh

Abstract

In Bangladesh, most croplands are situated in floodplains, enriched by numerous rivers and extensive freshwater wetlands. These areas also support productive open-water fisheries, crucial for supplying protein, generating income, creating jobs, and boosting the GDP. However, the widespread use of pesticides in these floodplains to protect crops and enhance food production leads to significant environmental issues. Agricultural pesticide residues enter water bodies through runoff, rainwater, drainage, seepage, and spray drift, contaminating natural water bodies and exerting continuous stress on aquatic life, including fish. Previous studies have detected pesticide residues in surface waters, sediments, and fish in Bangladesh, posing a major threat to wetland ecosystems. Research on freshwater fish species in Bangladesh has highlighted toxic effects on fish gonads, such as adhesion, inter-follicular space degeneration, ovigerous lamellae degeneration, necrosis, degenerated perinucleolar oocytes, cytoplasmic retraction in ovaries, and damage to sertoli cells. Additional observed effects include irregularly shaped seminiferous tubules, breakage of seminiferous tubules, and empty lumens in testes. Pesticides also inflict harm on other internal organs of fish, with gill effects like clubbing, reduction of gill filaments, telangiectasia of gill lamellae, hemorrhage, and damage to gill rakers. Kidney and liver damage include necrosis, cellular tissue degradation, acute cellular swelling, and irregular renal corpuscles, along with autolysis, vacuolation, and fatty changes in the liver. Developing embryos and larvae of freshwater fish are particularly vulnerable to the toxic effects of agro-pesticides. Studies reveal acute toxicity during early life stages, evidenced by deformities like edema, notochord deformity, caudal fin damage, yolk sac damage, posterior region damage, tissue fragmentation, black pigmentation on the yolk, body curvature, and lordosis in larvae. Exposed embryos exhibit deformities such as dark brown yolk sacs, notochord deformities, and broken eggshells. Mortality rates of fish embryos and larvae escalate with higher pesticide concentrations in water. Haemato-biochemical parameters serve as crucial indicators of pesticide exposure in fish studies, showing alterations in blood hemoglobin, glucose, RBC, WBC counts, and various erythrocytic abnormalities like twin cells, fusion, echinocyte formation, spindle-shaped, tear-drop, and elongated cells. Nuclear abnormalities include binucleated cells, nuclear buds, nuclear bridges, karyopyknosis, and notched nuclei. Research suggests that even at low concentrations, agro-pesticides disrupt physiological functions and life history traits of fish, adversely impacting the natural productivity and biodiversity of freshwater fish in Bangladesh.