Effects of Dietary Low-Molecular-Weight Fish Hydrolysate (LWFH) on Nonspecific Immunity and Antioxidant Capacity of Pacific White Shrimp (Litopenaeus vannamei)

Abstract:

In this study we investigated effects of low-molecular-weight fish hydrosate (LWFH) on nonspecific immune and antioxidant capacity in the hepatopancreas and the expression of some immunity-related genes in the digestive tract of Pacific white shrimp (Litopenaeus vannamei). A diet containing 30% of fishmeal was regarded as a high fishmeal diet (HFM), and a diet containing soybean meal that substitutes 50% of the fishmeal in HFM was considered as a low fishmeal basal diet (LFM). Five LFM diets were formulated by adding LWFH at incremental levels (0, 0.5%, 1.0%, 1.5% and 2.0%) to LFM, which were designated as LFM0, LFM0.5, LFM1.0, LFM1.5, and LFM2.0, respectively. The experimental diets were fed to L. vannamei of (0.44±0.02) g in a water recirculation system for 48 days. The nonspecific immunity and antioxidant indices, and the activities of acid phosphatase (ACP), alkaline phosphatase (AKP), total superoxide dismutase (T-SOD) and the content of malonaldehyde (MDA) in the hepatopancreas were measured to determine the effects of dietary LWFH. We studied the expression of immunity-related genes including IMD, Penaiedin 3a, LZM and Crustin using qRT-PCR. The results suggested that a certain amount of LWFH could significantly improve the activities of ACP, AKP and T-SOD while reducing the content of MDA in the hepatopancreas. Moreover, the relative expression of IMD, Penaiedin 3a, LZM and Crustin were up-regulated in the LFM1.5 group. Therefore, the plant proteins may not be an ideal substitute because they may reduce the nonspecific immunity and antioxidant capacity of L. vannamei. Our results also suggested that 1.0%–1.5% LWFH added in LFM might increase the expression of the disease resistance related genes and enhance nonspecific immunity and antioxidant capacity．