Effects of hydroxyl methionine selenium supplementation in low-fishmeal diet on growth, antioxidant ability and nitrite tolerance of Pacific white shrimp (Litopenaeus vannamei)

Selenium is one of the important trace elements in aquatic animals, which plays an important role in animal growth and antioxidant ability. Compared with inorganic Se, organic Se is better absorbed and has higher bioavailability and tissue accumulation in many aquatic animals. The present study was performed to investigate the effects of hydroxyl methionine selenium (HMSe) supplementation in low-fishmeal diet on growth performance, antioxidant ability and nitrite tolerance of Litopenaeus vannamei. In this experiment, L. vannamei with an initial body weight of 0.90±0.05 g was fed with low-fishmeal diets (15% fishmeal) supplemented with 0.000, 0.375, 0.750, 1.500 and 2.250 mg/kg HMSe respectively, named HMSe0, HMSe1, HMSe2, HMSe3 and HMSe4. Each group had 3 replicates with 50 shrimp in each tank (500 L). The shrimp was fed to visual satiation three times daily at 08:00, 14:00 and 19:00 h for 8 weeks. After the feeding trial, 12 h nitrite stress test was conducted. The results showed as follows: The finial body weight (FBW, 15.03-16.11 g), weight gain (WG, 1570.1-1689.8%) and feed efficiency (FE, 1.10-1.33) of L. vannamei increased firstly and then decreased with the increase of dietary HMSe level in the diet, and reached the maximum value in the HMSe2 group. With the increase of the dietary HMSe level, the feeding intake (FI) decreased firstly and then increased. There was no significant difference in protein efficiency ratio (PER) and survival rate (SR) in all groups. With the increase of dietary HMSe level, the contents of selenium in whole body and muscle both increased significantly, while the contents of crude protein and crude fat in L. vannamei increased firstly and then decreased, and reached the maximum in the HMSe2 group and HMSe1 group, respectively. The contents of moisture and ash showed no significant effects in all groups. The activities of serum glutathione peroxidase (GSH-Px) and hepatopancreas catalase (CAT) in the HMSe4 group were significantly higher than those in the HMSe0 group. With the increase of the dietary HMSe level, the activities of total superoxide dismutase (T-SOD) and glutathione S-transferase (GST) in hepatopancreas were increased firstly and then decreased. Nitrite stress for 12 h significantly decreased the survival rate of L. vannamei. The survival rate in the HMSe2 group was significantly higher than that in the HMSe0 group. After nitrite stress, the content of MDA in hepatopancreas increased, but the activities of GST, CAT and T-SOD in hepatopancreas decreased. Meanwhile, these negative effects could be relieved with appropriate HMSe supplementation. The optimal supplementation of HMSe for L. vannamei was 1.35 mg/kg based on survival rate under nitrite stress using the guadratic polynomial regression analysis. In conclusion, supplementing 0.75-1.35 mg/kg HMSe in low-fishmeal diet could improve the growth performance, feed utilization, antioxidant ability and nitrite tolerance of L. vannamei.