Ecofriendly synthesis of iron nanoparticles and their role in mitigation of multiple abiotic stresses in fish.

Aquatic animals are frequently exposed to environmental stressors such as elevated temperatures and various inorganic and organic contaminants. The present investigation examines the role of iron nanoparticles (Fe-NPs) in mitigating the combined effects of cadmium (Cd, 1/10th of LC50 0.69 mg L-1) toxicity and high-temperature stress (34 °C) in Pangasianodon hypophthalmus (striped catfish). Four treatments were designed in triplicate: a control group, a group exposed to Cd and high temperature (Cd + T), and two groups exposed to Cd + T but fed with Fe-NPs at 10 and 15 mg kg-1, respectively. Fe-NPs were biologically synthesized using fish waste (gill). Experimental diets were prepared by incorporating Fe-NPs at 0, 10, and 15 mg kg-1. Dietary supplementation with Fe-NPs significantly improved growth performance under Cd + T stress, including final weight gain %, specific growth rate, protein efficiency ratio, feed conversion ratio, relative feed intake, and daily growth index. Expression levels of growth genes GH and GHR1 in liver tissue were notably upregulated by Fe-NP-fed groups, while MYST expression was downregulated. Furthermore, stress and immune-related markers such as cortisol, HSP70, iNOS, CYP450, Caspase-3a, and TNF-α were significantly reduced in Fe-NP-treated groups compared to Cd + T and control groups, whereas Cd + T exposure alone markedly elevated these markers. Oxidative stress enzymes including catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferase (GST) in liver and kidney tissues were significantly elevated under Cd + T exposure, but their levels were reduced with dietary Fe-NP supplementation. Additionally, Fe-NPs at 10 and 15 mg kg-1 enhanced acetylcholine esterase activity in brain tissue compared to control and stressors group (Cd + T). Activities of alanine aminotransferase (ALT), aspartate aminotransferase (AST), lactate dehydrogenase (LDH), and malate dehydrogenase (MDH) in liver and gill tissues were significantly reduced in Fe-NP-fed groups under stress conditions. Importantly, dietary Fe-NPs also lowered Cd accumulation in various fish tissues. In conclusion, dietary supplementation with Fe-NPs at 10 and 15 mg kg-1 effectively mitigated the combined stress of Cd toxicity and elevated temperature in P. hypophthalmus by modulating gene expression, enhancing physiological performance, and alleviating cellular and metabolic stress.