Iron (Fe) is an essential micronutrient for fish, playing a crucial role in various physiological processes, including oxygen transport, enzymatic activity, and overall metabolic function. However, excessive concentrations of iron in aquatic environments can have harmful effects on fish health, leading to oxidative stress, impaired organ function, reduced growth, and even mortality. Currently, there are no widely accepted or effective therapeutic agents available to mitigate the toxic effects of elevated iron in catfish production systems. This lack of intervention strategies highlights the urgent need for alternative solutions to protect fish from iron-induced toxicity.
A promising strategy to mitigate waterborne iron toxicity in aquaculture is the incorporation of dietary supplements such as bentonite, a natural clay known for its strong adsorption properties. Given its ability to bind excess metals and prevent their systemic accumulation, the present study aimed to evaluate the protective effects of dietary bentonite in channel catfish (Ictalurus punctatus) exposed to elevated environmental iron levels. To assess this, three experimental diets were formulated: a control diet containing 0% bentonite, a diet supplemented with 2.5% bentonite, and another supplemented with 5.0% bentonite. Catfish from each dietary group were subjected to a high iron concentration of 9.5 mg/L (as Fe³⁺), representing 25% of the determined 96-hour LC50. Additionally, a non-exposed control group was maintained in parallel for each dietary treatment. The experiment was conducted in triplicate over a period of eight weeks to determine the long-term effects of dietary bentonite supplementation. Following exposure to Fe, significantly lower growth was observed for the fish group fed with the control diet in comparison to bentonite-supplemented (at either dose) fish groups. During iron exposure, Fe accumulation in the liver and plasma was significantly higher in the control diet group compared to bentonite-supplemented dietary groups. Likewise, Fe exposed group fed with the control diet showed oxidative stress in the liver based on significantly higher malondialdehyde (MDA) content as well as reduced catalase (CAT) and superoxide dismutase (SOD) activities, whereas activities of these enzymes increased significantly in dietary bentonite treatments. Overall, these findings demonstrate that dietary bentonite supplementation effectively mitigates waterborne iron toxicity in channel catfish by improving growth performance, reducing iron accumulation in tissues, and enhancing antioxidant enzyme activity. The results suggest that bentonite can serve as a practical and sustainable dietary intervention in catfish farming to counteract the adverse effects of elevated environmental iron levels.