Effect of yeast hydrolysate supplementation on the resistance of Pacific white shrimp, Litopenaeus vannamei , challenged with low salinity stress

Although Pacific white shrimp, Litopenaeus vannamei is a euryhaline shrimp species, when suffering from acute low salinity stress, the survival and physiological status of the shrimp may be affected. This study aimed to investigate whether the dietary yeast hydrolysate (YH) helped Litopenaeus vannamei to respond to acute low salinity stress. Firstly, shrimp (mean weight 15.82 ± 0.08g) were randomly assigned to two groups and fed two diets containing 0% YH (YH0) and 3% YH (YH3) four times daily at a salinity of 28. After a two-week feeding trial, some shrimp fed the two diets were transferred to salinity 4 and 20 mediums and others were transferred to salinity 28 as control for a low salinity stress. Samples of shrimp were collected at 0 h, 0.5 h, 1 h, 3 h, 6 h and 9 h after transferred. Results showed that Na/K-ATPase and phenoloxidase (PO) activities were not affected, while alkaline phosphatase (AKP) and acid phosphatase (ACP) activities decreased, but the superoxide dismutase (SOD) activity increased in shrimp fed diet with yeast hydrolysate before the low salinity stress (0 h). The Na/K-ATPase activity decreased at 1 h, 3 h and 6 h due to the decrease in salinity. The Na/K-ATPase activity of shrimp fed YH3 diet increased at 1 h and 9 h but decreased at 6 h compared with that fed YH0. The AKP activity decreased at 6 h, while the ACP activity decreased at 1 h and 3 h for the salinity stress. AKP and ACP activities of shrimp fed YH3 diet decreased at 3 h and 6 h compared with that fed YH0. The PO activity decreased at 0.5 h, 1 h, 3 h and 9 h because of the decrease in salinity. However, it increased in shrimp fed YH3 diet at 1 h compared with that fed YH0 diet. The SOD activity decreased at 3 h and 6 h due to the low salinity stress. The SOD activity of shrimp fed YH3 diet decreased at 0.5 h and 9 h compared with that fed YH0. Therefore, it was concluded that the ingestion of the feed containing yeast hydrolysate improved the defence against low salinity stress by modulating the activity of Na/K-ATPase, PO and SOD enzymes, while the diet factor has less impact on the AKP and ACP activities of the organism compared with the culture salinity.