Nanozymes as a novel solution for oxidative stress reduction and nitrogen compound removal in aquatic systems: a...

Antioxidants in fish are vital biomarkers when exposed to pollutants that cause oxidative stress. Among the most important components of the antioxidant defense system are the enzymes superoxide dismutase (SOD) and catalase (CAT). This study aimed to evaluate the potential of certain nanomaterials as nanozymes by mimicking the activity of SOD and CAT enzymes when added to the diet of common carp, simultaneously, removing the efficacy of nitrogen waste. To evaluate the effect of nanozymes on common carp fish, six types of experimental diets were used over 84 days. The study included six groups: a control group (T1) on a standard diet, and five groups supplemented with 1 mg kg⁻¹ of potassium dichromate (K₂Cr₂O₇). Among these, T3 and T4 also received 1 mg kg⁻¹ and 5 mg kg⁻¹ of CeO₂ nanoparticles, respectively, while T5 and T6 were given 1 mg kg⁻¹ and 5 mg kg⁻¹ of Fe₃O₄ nanoparticles, respectively. The experiment aimed to study the effects of K₂Cr₂O₇ combined with varying doses of CeO₂ and Fe₃O₄ nanoparticles. The results of the current study indicated a significant reduction (P ≤ 0.05) in certain nitrogenous compounds (ammonia and nitrates) in water in nanozyme treatments. The study also demonstrated a significant improvement (P ≤ 0.05) in productive performance in (T6), a significant decrease (P ≤ 0.05) in liver enzyme activity in blood serum in (T3), and a significant increase (P ≤ 0.05) in glutathione peroxidase (GPx) enzyme activity in (T5). Furthermore, there was a significant increase (P ≤ 0.05) in the gene expression of the enzymes SOD and CAT in (T4), as well as the gene expression of the GPx enzyme in (T6). The current study concludes that CeO₂ and Fe₃O₄ nanoparticles can be added to fish diets as nanozymes to combat oxidative stress in fish by mimicking the activities of the body's antioxidant enzymes. Nanozymes seem to reduce nitrogenous pollutants via adsorption or possibly oxidation.