Protective role of selenium and selenium-nanoparticles against multiple stresses in Pangasianodon hypophthalmus

Pollution and climate change pose significant threats to aquatic ecosystems, with adverse impacts on aquatic animals, including fish. Climate change increases the toxicity of metal in aquatic ecosystems. To understand the severity of metal pollution and climate change, an experiment was conducted to delineate the mitigation potential of selenium (Se) and selenium nanoparticles (Se-NPs) against lead (Pb) and high temperature stress in Pangasianodon hypophthalmus. For the experiment, five isonitrogenous and isocaloric diets were prepared, varying in selenium supplementation as Se at 0, 1, and 2 mg kg^-1 diet, and Se-NPs at 1 and 2 mg kg^-1 diet. The fish in stressor groups were exposed to Pb (1/20th of LC₅₀ concentration, 4 ppm) and high temperature (34 °C) throughout the experiment. The results demonstrated that dietary supplementation of Se at 1 and 2 mg kg^-1 diet, as well as Se-NPs at 1 mg kg^-1 diet, significantly reduced (p < 0.01) the levels of lactate dehydrogenase and malate dehydrogenase in both liver and muscle tissues. Additionally, the levels of alanine aminotransferase and aspartate aminotransferase in both gill and liver tissues were significantly decreased (p < 0.01) with the inclusion of Se and Se-NPs in the diets. Furthermore, the enzymes glucose-6-phosphate dehydrogenase in gill and liver tissues, fructose 1,6-bisphosphatase in liver and muscle tissues, and acid phosphatase in liver tissue were remarkably reduced (p < 0.01) due to the supplementation of Se and Se-NPs. Moreover, dietary supplementation of Se and Se-NPs significantly enhanced (p < 0.01) the activity of pyruvate kinase, glucokinase, hexokinase, alkaline phosphatase, ATPase, protease, amylase, lipase, and RNA/DNA ratio in the fish. Histopathological examination of gill and liver tissues also indicated that Se and Se-NPs protected against structural damage caused by lead and high-temperature stress. Moreover, the study examined the bioaccumulation of selenium and lead in muscle, water, and diets. The aim of the study revealed that Se and Se-NPs effectively protected the fish from lead toxicity and high-temperature stress, while also improving the function of cellular metabolic enzymes in P. hypophthalmus.