Dietary cholesterol enhances osmoregulation, antioxidant defenses and immune response of Litopenaeus vannamei to alleviate the macromolecular damage induced by salinity stress

Cholesterol is an important essential nutrient for crustaceans. This experiment investigated the effects of dietary cholesterol on the osmoregulation, antioxidant defense, immune response and salinity stress resistance of Pacific white shrimp (Litopenaeus vannamei). Six diets (Chol 1.0, Chol 1.4, Chol 1.8, Chol 2.2, Chol 2.6, and Chol 3.0) with cholesterol levels of 0.1%, 0.14%, 0.18%, 0.22%, 0.26% and 0.30% were prepared and fed on shrimp (1.27 ± 0.18 g) for 56 d, followed by the low salinity stress experiment for 144 h. Sampling was conducted at 56 d and 24, 72, 144 h during salinity stress. At 56 d, cholesterol enhanced the growth performance of L. vannamei by promoting transport and absorption of endogenous lipid. Dietary 0.22%–0.30% cholesterol could enhance the antioxidant defense and immune response of shrimp. After salinity stress, Na+, Cl− and K+ ion concentrations and osmolality in hemolymph were decreased significantly (P < 0.05), and the Na+ concentration and osmolality of hemolymph in Chol 2.2–3.0 groups were significantly higher than those in Chol 1.0–1.4 groups (P < 0.05). After 24 h and 72 h of salinity stress, Na+/ K+- ATPase (NKA) activity in Chol 2.2–3.0 groups was significantly higher than that in Chol 1.0–1.4 groups (P < 0.05). The plasma dopamine (DA), norepinephrine (NE) and serotonin (5-HT) contents increased significantly at 24 h and recovered at 144 h in all groups (P > 0.05) with no significant differences in biogenic amines contents among all groups at the same time points (P > 0.05), indicating that cholesterol could improve the osmoregulation of L. vannamei by directly enhancing NKA activity independent of the regulation of biogenic amines. Dietary 0.26%–0.30% cholesterol could enhance the osmoregulation and salinity stress resistance of shrimp and protect against biomacromolecule damage induced by oxidative stress and ion toxicity. Insufficient cholesterol intake (below 0.1%) may presumably cause the death of shrimp by affecting the NKA conformation. Under physiological conditions, the optimum level of dietary cholesterol in shrimp feed was about 0.22%, while it was 0.26% - 0.3% under salinity stress.