Search

This study was conducted to evaluate the effects of Bacillus licheniformis and combined herbs extracts on the physiological and immune characteristics, intestinal microbiota, and vibriosis resistance of sea cucumber Apostichopus japonicus. The sea cucumbers were fed with basal diets supplemented with B. licheniformis (B group), combined herbs extracts (C group), or both (BC group). The BC group exhibited the better growth performance and higher digestive and immune enzyme activities, whereas the lowest parameters appeared in the control group. This revealed that dietary B. licheniformis and combined herbs extracts in combination could improve digestion, food intake, phosphatase-responsiveness, and oxidation resistance more efficiently compared with the other groups. The BC group was also more capable of regulating intestinal flora balance of sea cucumbers by increasing the beneficial bacteria related to energy synthesis and metabolic conversion, and inhibiting the potential pathogens associated with organic damage and metabolic disorders. Furthermore, the BC group showed greater ability of improving disease resistance by reducing the cumulative mortality rates and the counts of Vibrio splendidus. These results collectively demonstrated that dietary B. licheniformis and combined herbs extracts could improve the physiological and immune parameters, optimize the microbial community, and enhance the resistance to vibriosis of sea cucumbers, and the health-promoting effects were more obvious by supplying them in combination.

In order to understand the effects of seasonal change on the immunity of sea cucumber Apostichopus japonicus cultured in pond, A. japonicus with body weight of 12.2 ± 4.5 g (sample A) and 32.6 ± 7.1 g (sample B), respectively, were collected monthly and randomly from a typical pond during a year cycle and employed for the evaluation of immunocompetence. Simultaneously, the environmental factors in the pond including water temperature, pH, salinity and dissolved oxygen (DO) were measured using a handheld multiparameter meter. The activities of acid phosphatase (ACP), alkaline phosphatase (ALP), lysozyme (LYZ), phenoloxidase (PO), superoxide dismutase (SOD), catalase (CAT) and myeloperoxidase (MPO) in the coelomic fluid were selected for the evaluation of A. japonicus immunocompetence and determined using biochemical methods. The results showed that in both samples, the activities of all determined enzymes had small values in winter and early spring, and LYZ, CAT and MPO activities also presented small values in summer, suggesting that pond‐cultured A. japonicus underwent immunosuppression twice during a year cycle, and the immunosuppression occurred in winter and early spring was more severe than that occurred in summer. In addition, most of the determined enzymes showed different variations between the two samples, and had significantly negative correlation with protein concentration, which was significantly and negatively correlated with water temperature, revealing that body weight and water temperature might have crucial effects on the immunity of A. japonicus cultured in pond.

The immune-related enzymes in marine animals are very sensitive to divalent metal ions. To investigate the roles divalent metal ions play in the influence on the immunity of sea cucumber Apostichopus japonicus, one of the most important commercial species in Asian countries, the effects of eight divalent metal ions at concentrations of 2.5, 5, 10, 15, 20, 25 and 30 mmol L−1 on the activities of superoxide dismutase (SOD), phenoloxidase (PO), acid phosphatase (ACP), alkaline phosphatase (AKP) and myeloperoxidase (MPO) in coelomic fluid were determined with the nitro blue tetrazolium chloride (NBT) method, dopachrome formation method, p-nitrophenyl phosphate (pNPP) method and 3,3′,5,5′-tetramethyl benzidine (TMB) method. The results indicated that Mg2+ enhanced the activities of SOD, PO, ACP and AKP significantly and showed no obvious effect on MPO activity; Zn2+ increased the activities of SOD, ACP and AKP, and showed no obvious effect on the activities of PO and MPO; Cu2+ enhanced the activities of ACP, AKP and MPO and activated SOD and PO at a certain concentration range; Ca2+ and Mn2+ inhibited the activities of ACP and AKP; Fe2+ had strong inhibitory effect on SOD activity; Pb2+ showed inhibitions on the activities of SOD, PO, ACP and AKP; and Cd2+ inhibited MPO activity greatly. The data obtained in this study collectively suggest that Mg2+, Zn2+ and Cu2+ have potential in promotion of A. japonicus immunity, while Ca2+, Fe2+, Pb2+, Cd2+ and Mn2+ might be limiting factors to the immune response of A. japonicus.