Evaluation of largemouth bass (Micropterus salmoide) fed selenium yeast diets: Growth, histopathology, antioxidant ability, and apoptosis

The objective of this study was to investigate the effects of selenium yeast on the growth, histomorphology, antioxidant capacity and apoptosis of largemouth bass (Micropterus salmoide). The five iso-nitrogen and iso-lipid feeds were supplemented with selenium yeast levels of 0, 0.5, 1.0, 1.5 and 2.0 mg/kg, respectively. The 525 largemouth bass (initial body weight: 11.48 +/- 0.43 g) were equally divided into 15 buckets (three buckets per feed treatment) for a 67-day feeding experiment. The results showed that the addition of 1.5 and 2.0 mg/kg of selenium yeast significantly reduced weight gain rate, and specific growth rate (P < 0.05), disorganized the structure of liver cells and exacerbated the vacuolation of liver tissue in largemouth bass. The activities of glutathione peroxidase and superoxide dismutase in serum were significantly increased by 1.0 mg/kg selenium yeast (P < 0.05). After selenium yeast was supplemented, villus length and villus width were significantly increased (P < 0.05), NO contents and respiratory burst activities in hematocyte were not significantly changed (P > 0.05). With the addition of 1.5 mg/kg of selenium yeast, the relative expression of growth hormone 1, insulin-like growth factor-1, superoxide dismutase, catalase, Kelch-like ECH-associating protein 1, and nuclear factor erythroid 2 related factor 2 in hematocyte was significantly increased (P < 0.05). The significantly lowest percentage of apoptotic hematocyte was also seen in the 1.5 mg/kg selenium yeast addition group (P < 0.05). Overall, the supplementation of 1.5 mg/kg selenium yeast was not conducive to the growth and liver development of largemouth bass, but it could improve the antioxidant capacity of hematocyte and inhibit the apoptosis. It provided a theoretical basis for the enhancement of immune capacity during the farming of largemouth bass.