Effects Of Dietary Administration Of Several New Immunostimulants On Growth Performance, Survival, Immune Response And Disease Resistance Of Juvenile Large Croaker, Pseudosciaena Crocea

Feeding trials were conducted to examine the effect of dietary administration of Bacillus subtilis and fructooligosaccharide, Bacillus subtilis and chitosan, glycyrrhizi acid on growth performance, survival,immune response and disease resistance of juvenile large yellow croaker, Pseudosciaena crocea. The experiments were conducted in seawater floating net cages(1.5×1.5×2.0 m) for 70 days.During the experimental period, the water temperature ranged from 22.5 to 31.5℃,the salinity from 28 to 33 and the dissolved oxygen content was approximately 6 mg 1-1.Results of the present study are presented as follows:1.Nine practical diets were formulated to contain three levels of Bacillus subtilis (0.0 (control),0.5×107cfu/g and 1.0×107cfu/g), and each Bacillus subtilis level with three fructooligosaccharide levels (0 (control),0.2% and 0.4%). Each diet was randomly assigned to triplicate groups of juvenile large yellow croaker. The result showed that at each dietary fructooligosaccharide level, dietary supplementation of 1.0×107cfu/g Bacillus subtilis significantly increased the specific growth ratio (SGR) (P<0.01)and feed efficiency ratio (FER) (P<0.05) compared with the Bacillus subtilis-deficient group. The immune assay showed that at each fructooligosaccharide level, serum superoxide dismutase (SOD) activity in fish fed the diet with 1.0×107cfu/g Bacillus subtilis was significantly enhanced compared with the Bacillus subtilis-deficient group (P<0.05).At each fructooligosaccharide level,fish fed diets with 0.5<107cfu/g Bacillus subtilis showed significantly improved serum lysozyme activity compared to the Bacillus subtilis-deficient group (P<0.05).Results of challenge test showed that 7 days accumulated mortality after bacterial infection was significantly lower in fish fed the diet with 1.0×107cfu/g Bacillus subtilis (P<0.05), at each fructooligosaccharide level.There was no interactional effect between the effect of dietary fructooligosaccharide and Bacillus subtilis on growth performance, immune response and disease resistance of juvenile large yellow croaker. These results showed that dietary supplementation of Bacillus subtilis (0.5×107cfu/g-1.0×107cfu/g) improved growth, feed efficiency ratio, nonspecific immune response and disease resistance of juvenile large yellow croaker.2.Nine practical diets were formulated to contain three levels of Bacillus subtilis (0 (control),0.5×107cfu/g and 1.0×107cfu/g), and each Bacillus subtilis level with three chitosan level (0 (control),0.3% and 0.6%).Each diet was randomly assigned to triplicate groups of juvenile large yellow croaker. The results showed that there were no significant differences in the SGR, survival, FER and hepatosomatic index (HSI) among experimental treatments. The immune assay showed that at each Bacillus subtilis level, respiratory burst activity of kidney macrophage in fish fed the diet with 0.3% chitiosan was significantly enhanced compared with the chitoan-deficient group (P<0.05). At each Bacillus subtilis level,fish fed chitosan-supplemented diets showed improved serum lysozyme activity compared to those fed chitosan-deficient diets (P<0.05).The result of challenge test showed that at each chitosan level,7 days accumulated mortality after bacterial infection was significantly lower in fish fed Bacillus subtilis-supplemented diets than in fish fed Bacillus subtilis-deficient diets (P<0.01).There was no interactional effect between the effects of dietary chitosan and Bacillus subtilis on growth performance, immune response and disease resistance of juvenile large yellow croaker. These results showed that dietary supplementation of chitosan (0.3-0.6%) improved nonspecific immune response, and dietary supplementation (0.5×107cfu/g-1.0×107 cfu/g) of Bacillus subtilis enhanced disease resistance of juvenile large yellow croaker.3.A series of experiments were conducted with the macrophages isolated from head kidney of large yellow croaker, Pseudosciaena crocea. Graded concentration of tryptophan with 0.00,0.03,0.06,0.12,0.24 and 0.48mM were added to the culture medium for a 6h incubation. After then, samples were taken for the measurements of respiratory burst, losozyme activity, superoxide dismutase activity and catalase activity. The results show that as the concentration of tryptophan increased, the respiratory burst activity first increased then decrease, and the value of respiratory burst activity at 0.12mM group was significantly higher than the control (P<0.05).With increasing concentration of tryptohan, SOD also first increased then decreased. When the tryptophan concentration was 0.06-0.48mM, the values of SOD were significantly higher than the control (P<0.05).However, CAT and lysozyme activity were independent of the tryptophan concentration (P>0.05).This result indicated that moderate concentration of tryptophan enhanced the nonspecific immune response of kidney macrophage of large yellow croaker in vitro.