The Research On Frequency Of Administration Of Immunostimulants And Immunity Fatigue For White Shrimp Litopenaeus Vannamei And Sea Cucumber Apostichopus Japonicus

A six-week growth trial was conducted to compare the effects of different feeding strategies of dietary immunostimulants on the growth and immunity of white shrimp Litopenaeus vannamei (4.70±0.20 g). The six feeding strategies were as follows:(1) shrimps were fed with immunostimulant-free basal diet (C); (2) fed with dietaryβ-glucan (2000 mg/kg) continuously (CB); (3) fed with dietary glycyrrhizin (600 mg/kg) continuously (CG); (4) fed with dietaryβ-glucan (2000 mg/kg) for 7 days, then with basal diet for 7 days, and so on (B:C=7:7); (5) fed with dietaryβ-glucan (200 mg/kg) for 2 days, then with basal diet for 5 days, and so on (B:C=2:5); (6) fed with dietaryβ-glucan (2000 mg/kg) for 7 days, then with dietary glycyrrhizin (600 mg/kg) for 7 days, and so on (B:G=7:7). The total haemocyte count (THC), the superoxide anion, activities of phenoloxidase (PO) and superoxide dismutase (SOD) in serum were used to evaluate the immunities of shrimp. At the same time, the specific growth rate (SGR) was used to evaluate the growth performance. The results showed that compared with glycyrrhizin,β-glucan could maintain the immunity of shrimp at a higher level during the experimental period. However, continuously applyingβ-glucan or glycyrrhizin into the diet caused immunity fatigue in L. vannamei. Discontinuous administration ofβ-glucan or glycyrrhizin could eliminate the immunity fatigue. Shrimps fed with dietaryβ-glucan two days following basal diet five days (B:C=2:5) showed the highest SGR. It was concluded that the feeding strategy of B:C=2:5 is most suitable for L. vannamei.A four weeks trial was conducted to compare the effects ofβ-glucan, mannan-oligosaccharide (MOS) and their three alternate modes on the growth, immunity and resistance against Vibrio splendidus of sea cucumbers Apostichopus japonicus (6.80±0.30g). The sea cucumbers fed with immunostimulants showed higher special growth rate (SGR) and lower cumulative incidence than that of sea cucumbers fed with basal diet (control). In all groups, highest SGR was observed at the group of feeding sea cucumbers withβ-glucan diet seven days and MOS diet seven days while sea cucumbers fed with P-glucan diet two days and MOS diet five days alternately showed the lowest cumulative incidence. When sea cucumbers were fed withβ-glucan, the immune parameters increased and were significantly higher than control on the 4th day. But the total coelomocytes counts (TCC) and superoxide anion decreased and were without significant difference compared with control group on the 18th day. TCC of the sea cucumbers fed with MOS was significantly higher than that of control group on the 15th day and superoxide anion on 11th day. These two parameters were not different significantly compared with that of the control group on the 29th day but were still higher than that of the control group. The superoxide dismutase and phagocytic rate of the sea cucumbers fed withβ-glucan and MOS continuously were significantly higher than that of control group during the experiment. The sea cucumbers fed withβ-glucan and MOS alternately showed all four immune parameters significantly higher than that of the control group during the experiment and the phagocytic rate was significantly higher than that of the sea cucumbers fed continuously. Overall, alternate feeding P-glucan and MOS could take advantage of both to enhance the growth, immunity and resistance to V. splendidus. In three alternate modes, the schedule that feedingβ-glucan diet two days following MOS diet five days alternately was most suitable for sea cucumbers.