Effects Of Several Immunstimulants On The Non-specific Immune Response And Disease Resistance Of Japanese Flounder (Paralichthys Olivaceus)

Five experiments are conducted to investigate the effects of dietary vitamin C, vitamin E, glucan, n-3 HUFA, iron and zinc on the non-specific immune response and disease resistance to Edwardsiella tarda for Japanese flounder (Paralichthys olivaceus).Expriment I . A feeding experiment was conducted to investigate the effects of dietary vitamin E (supplied as DL-tocopheryl acetate) and n-3 HUFA on the non-specific immune response and disease resistance in Japanese flounder (Paralichths olivaceus). Nine practical diets were formulated to contain three levels of vitamin E (0, 80, 200 mg kg-1), and each vitamin E level with three glucan levels (0, 0.5 %, 1.5 %). Each diet was randomly assigned to triplicate groups of Japanese flounder (initial body weight: 40.5 + 1.0 g) in a re-circulation system. Fish were fed twice daily to satiation at 7:00 and 18:00 for 12 weeks. The results showed that muscle a -tocopherol and n-3 HUFA contents reflected dietary treatments well. However, the supplementation of dietary n-3 HUFA significantly decreased muscle a -tocopherol content (P<0.05). Alternative complement pathway activity (ACH50) was significantly increased with dietary vitamin E at 0.5% n-3 HUFA level (P<0.05). ACH50 also significantly increased with increasing dietary n-3 HUFA levels at 80 and 200 mg kg-1 vitamin E (P0.05). The highest ACH50 (199.9 U ml-1) was found in fish fed the diets supplemented with 200 mg kg-1 vitamin E and 1.5% n-3 HFUA. Fish fed the diet supplemented with 200 mg kg-1 vitamin E and 1.5% n-3 HUFA had significant higher lysozyme activity (131.7 U/ml) compared with fish fed diets without supplementation of n-3 HUFA or supplemented with 80 mg kg-1 vitamin E (P<0.05). In the disease resistance experiment, supplementation of dietary vitamin E and n-3 HUFAsignificantly decreased cumulative mortality and delayed the days to first mortality after 7-day E. ictalur challenge (P0.05). In addition, under the experiment conditions, dietary vitamin E and n-3 HUFA had synergistically effect on non-specific immune response and disease resistance of Japanese flounder (P<0.05).Expriment . A feeding experiment was conducted to investigate the effects of dietary vitamin C (supplied as L-ascorbyl-2-polyphosphate) and P- glucan on the non-specific immune response and disease resistance in Japanese flounder (Paralichthys olivaceus). Nine diets were formulated to contain three levels of vitamin C (0, 500 and 2000 mg ascorbic acid kg-1 diet), and each vitamin C level with three glucan levels (0, 0.3 and 0.6%). Each diet was randomly assigned to triplicate groups of Japanese flounder (initial body weight: 40.5?.0 g) in a re-circulation system. Fish were fed twice daily to satiation at 7:00 and 18:00 for 12 weeks. The results showed that dietary vitamin C significantly improved the specific growth rate (SGR) and alternative complement activity (ACH50) (P0.05), while no significant effects were found in respiratory burst activity, lysozyme activity and disease resistance to Edwardsiella tarda. In the absence of dietary vitamin C, dietary glucan significantly increased ACH50 and respiratory burst activity. Fish fed glucan-deficiency diets had significantly higher cumulative mortality than those fed diets supplemented with 0.6% glucan after 7 days following E. tarda exposure in the presence of dietary vitamin C. Furthermore, the days to first mortality was significantly later for fish fed diets with 0.6% glucan when fish were fed diets with 500 mg kg-1 vitamin C (PO.05). The interaction between dietary vitamin C and glucan had significant effects on ACH50, respiratory burst activity and cumulative mortality (PO.05). These results suggest that 3 -glucan can be used in the diet to improve the non-specific immune responses, and prevent or reduce mortality caused by E. tarda in Japanese flounder. The results also show glucans have more active effect on immunity in fish then vitamin C by oral administration. Vitamin C and glucan had synergistic effect on the immunity and disease resistance in Japanese flounder.Expriment II...