Effects of crude extracellular protein and crude intracellular polysaccharides of Vibrio alginolyticus on the growth, energy metabolism regulation and WSSV resistance of Litopenaeus vannamei

This study aimed to investigate the effects of adding crude extracts of the extracellular protein (Ex-Pro) and intracellular polysaccharides (In-Poly) of Vibrio alginolyticus to diets, at a dosage of 10 g/kg, on the growth, energy metabolism and WSSV (White Spot Syndrome Virus) resistance of Litopenaeus vannamei (initial weight, 0.88 +/- 0.04 g/shrimp). Growth and survival rate were not significantly affected by the crude extracts (p > 0.05). Shrimp fed Ex-Pro crude extracts showed higher succinate dehydrogenase (SDH) activity in the hepatopancreas and muscle but lower lactate dehydrogenase (LDH) activity in the muscle (p < 0.05). The activities of hexokinase (HK), pyruvate kinase (PK), LDH and SDH in the hepatopancreas and the activity of SDH in the muscle were significantly increased by feeding In-Poly crude extracts (p < 0.05). In contrast, the content of fatty acid synthase (FAS) in the muscle was significantly reduced by the crude extracts (p < 0.05). The contents of glucose and triglyceride and the activity of the electron transport system in the hepatopancreas were significantly increased by the crude extracts (p < 0.05), and the WSSV resistance of the shrimp was increased. These results indicated that the Ex-Pro and In-Poly crude extracts of V. alginolyticus could affect energy metabolism, and there was a correlation between WSSV resistance and energy metabolism in L. vannamei.