Effect of dietary organic and inorganic selenium on some antioxidant defence system parameters in rainbow trout (Oncorhynchus mykiss)

The purpose of this study was to investigate the effect of organic and inorganic selenium in the diet of rainbow trout on changing of malondialdehyde (MDA) and some liver antioxidant enzymes including aspartate transaminase (AST) and glutathione peroxidase (GPX). For this purpose, 810 rainbow trout fry with an average weight of 50.6±2.2 g were randomly fed with supplemented diets: 0 (control), 0.15, 0.30, 0.45, and 0.60 mg of organic (selenium-enriched yeast) and inorganic (sodium selenite) selenium per kg of feed with 3 replicates for 60 days. At the end of the experiment, the results showed that the amount of GPX enzyme activity in fish fed with 0.60 mg of organic selenium per kg diet reached a maximum of 5.49±0.62 IU/L, which was significantly different with other treatments (p<0.05). Addition of different sources of selenium to the diet caused a decreasing trend in AST enzyme, although the addition of organic selenium more than 0.45 mg kg was significantly reduced this enzyme and its lowest value was obtained in 0.60 mg kg of organic selenium (49.30±1.84 IU/L) (p<0.05). The lowest MDA level was observed in 0.60 mg kg of organic selenium (19.10 ± 0.76 μmol/L) compared to the other treatments (p <0.05), but the level of MDA among fish fed with inorganic selenium was only reduced in 0.60 mg kg of inorganic selenium and other treatments showed no significant difference (p> 0.05). Overall, considering the importance of selenium in GPX enzyme activity and based on the results, adding of organic selenium, especially at 0.60 mg/kg feed, had a greater effect on enhancing the antioxidant ability of rainbow trout compared to sodium selenite.