Alterations in histopathological features and brain acetylcholinesterase activity in stinging catfish Heteropneustes fossilis exposed to polluted river water

Responses of stinging catfish (Heteropneustes fossilis) to pollution were studied in three freshwater rivers, namely Buriganga, Turag, and Shitalakkhya (Dhaka, Bangladesh), which are potentially affected by anthropogenic pollution originating from industrial and sewage dumping. Partial parameters about water quality (temperature, dissolved oxygen, and pH) and seasonal plankton fluctuation were recorded at wet and dry seasons. Histopathology and acetylcholinesterase (AChE) activity were used as biomarkers to assess water toxic effects in 7-and 10-day exposures of H. fossilis to three rivers waters, respectively. The lowest level of dissolved oxygen was recorded as 0.7 ± 0.1 mg/l, and the lowest count of plankton genera was 21 at lean period. Furthermore, the 7-day exposure of fish to polluted water abruptly altered the normal structure of various organs. Major structural damages were partial and total epidermal loss, dermis and muscle separation, melanin pigment and vacuole in skin muscle; missing of lamellae, clubbing, fungal granuloma, hyperplasia and hemorrhage in gills; hyperplasia, hemorrhage, pyknosis, vacuole, necrosis, nuclear alteration, fatty degeneration, lipid droplets in liver; degenerating glomerular and tubule, hemorrhage, pyknosis and vacuole in kidneys; and scattered spermatozoa and prominent interstitial space in the testis. After subsequent exposure to polluted water, a significant (P < 0.05) inhibition of AChE activity in the fish brain was observed with the following order of potency: 102.00 ± 5.00 nmol/min/mg protein (Turag) ≥ 104.00 ± 5.00 nmol/min/mg protein (Buriganga) > 130.67 ± 3.51 nmol/min/mg protein (Shitalakkhya). This study confirmed the utility of biomarkers in biomonitoring studies and reflected the potential hazards of pollution to aquatic biota.