Dietary supplementation of astaxanthin is superior to its combination with Lactococcus lactis in improving the growth performance, antioxidant capacity, immunity and disease resistance of white shrimp (Litopenaeus vannamei)

A four-week feeding trial, followed by a challenge test, was conducted to evaluate the effects of Lactococcus lactis and astaxanthin on the growth performance, digestive ability, antioxidant capacity, immunity, and disease resistance of Litopenaeus vannamei against Vibrio alginolyticus. Specifically, shrimp were randomly allocated into 12 tanks (100 shrimp per tank), and divided into 4 groups with 3 replicates. Shrimp were fed on either a control (CK) or three other treatment diets by supplementing L. lactis at 1 x 10(8) CFU g(-1) diet (L), astaxanthin at 250 mg kg(- 1) diet (A) and L. lactis at 1 x 10(8) CFU g(-1) diet combined with astaxanthin 250 mg kg(- 1) diet (LA). Results indicated that treatment diets significantly improved growth performance and increased the activity of digestive enzymes relative to the control diet. Particularly, the highest parameters were recorded in shrimp fed on astaxanthin alone. Moreover, statistical analysis revealed significant differences in antioxidant and immune enzymes activities between shrimp in the CK and A groups. From the results of the challenge test, shrimp fed on treatment diets all had significantly lower mortality as compared to the control diet, and shrimp fed on astaxanthin alone had the lowest mortality. Dietary supplementation of astaxanthin alone significantly increased the relative expression of Cru, Pen-3 alpha, SOD and LZM and decreased the relative expression of proPO in the gut of shrimp as compared to the control diet. The results indicates that the relative expression levels of most selected immune-related genes were significantly up-regulated in shrimp fed on astaxanthin alone, which may explain the best disease resistance observed in this group. Taken together, the findings of this study suggest that astaxanthin can positively affect the growth performance, digestive ability, antioxidant capacity, immunity, and disease resistance of L. vannamei against V. alginolyticus. Notably, these effects are superior to those induced by L. lactis alone or in combination with L. lactis.