Effects of feeding selenium yeast fortified Artemia on the growth, survival rate, fatty acid composition, liver and intestinal tissue structure and stress resistance of largemouth bass (Micropterus salmoides ) larvae

At present, there are still some problems in the cultivation of aquatic fry in the market, such as the low survival rate caused by the inappropriateness of food. Therefore, it is particularly important to meet the nutritional needs of fish larvae at the stage of breeding high-quality fry. The purpose of this study was to investigate the effects of feeding selenium-enriched yeast on growth, survival rate, fatty acid composition, liver and intestinal structure, and stress resistance of Micropterus salmoides larvae. The five selenium supplementation concentrations of 0 (Y-se0), 5 (Y-se5), 10 (Y-se10), 15 (Y-se15) and 20 (Y-se20) mg/L were set to enhance the selenium nutrition of the M. salmoides larvae, and the enhanced selenium larvae were fed to 3000 M. salmoides larvae in glass tank (2.1 mg/ind., 200 ind./tank) for 20 days. At the end of the feeding experiment, 10 larvae per tank were placed in the 35 °C thermostatic water bath for acute temperature stress test. The results showed as follows: ① The survival rate (78.67%±1.55%), final body weight (49.28±1.56) mg, body length (1.35±0.05) cm and specific growth rate (15.78±0.16) of the Y-se15 group were significantly higher than those of the control group (P<0.05), but there were no significant differences in the condition factor (CF) among all groups (P>0.05). ② EPA content in the Y-se5 group was significantly lower than that of the control group (P>0.05); the DHA/EPA value of Y-se5 and Y-se15 groups were significantly higher than that of the control group (P<0.05). ③ The catalase (CAT) activity in the liver of Y-se10, Y-se15 and Y-se20 groups were significantly higher than that of the control group (P<0.05), and the glutathione peroxidase (GSH-Px) activity in the liver of all treatment groups were significantly higher than that of the control group (P<0.05). However, the content of malondialdehyde (MDA) in the liver of Y-se10, Y-se15 and Y-se20 groups were significantly lower than that of the control group (P<0.05), and the activity of total superoxide dismutase (T-SOD) exhibited no significant difference between all the treatment groups with the control group (P>0.05). ④ The vacuolation of liver tissue in the Y-se15 group was much less, and the intestinal villus length in the selenium yeast supplemental groups were significantly higher than that of the control group (P<0.05). ⑤ Under the 35 °C stress condition, the survival time of the Y-se15 group was significantly higher than that of the control group (P<0.05). In conclusion, the supplementation of selenium yeast at 15 mg/L level could significantly increase the growth, survival rate and DHA/EPA level of M. salmoides larvae, and improve the health status of fish by the enhancement of the organism's antioxidant and anti-stress ability. This study preliminarily explored the effect of feeding artemia nauplii with enriched yeast selenium on M. salmoides larvae, with the aim of providing reference for further improving the technology of nutrient fortification in the open-mouth diet of aquatic animal seedlings and promoting the high-quality development of aquaculture.