Potential benefits of natural bentonite as a water clarifier on ammonia removal, performance, immunity, antioxidant, and histology of Dicentrarchus labrax

Clay minerals such as bentonite (BNT) have recently drawn attention as non-nutritive additives in aquaculture, which can maintain water quality and maximize productivity. As water additives, four levels of natural BNT—0, 1.5, 3, and 4.5 g/liter (‰)—were evaluated. Juvenile European seabass (Dicentrarchus labrax) were stocked in fiberglass tanks and fed a commercial diet of 46/16 (protein/fat) for 56 days. The results showed that the BNT-treated groups had significantly reduced NH₃ content (p < 0.05) than the control group. Fish performance improved significantly in the BNT-treated groups. Blood biochemistry, digestive enzymes, liver and kidney function improved significantly with increasing BNT levels, in addition to the improvement of immune and antioxidant parameters, i.e., IGM, cortisol, MDA, catalase, TAC, and GPx, in comparison to the control group. Data on the gills, intestine, and stomach histology showed that the BNT-treated groups had healthier organs. However, the liver histomorphology reveals that hepatic vacuolations did not improve in the BNT-treated groups with the exception of the B3 group. Besides, pancreatic sections were normal in all BNT-treated groups. Therefore, natural BNT can be recommended for application in marine aquaculture at a level of 3 g/L, to reduce ammonia and improve fish growth, health and immunity.