Effects Of Several Immunostimulants On The Growth Performance, Non-specific Immunity And Disease Resistance Of Cobia,(Rachycentron Canadum)

The present study was performed to investigate the effects of dietary on the growthperformance, non-specific immunity and protection against Vibrio harveyi infection incobia, Rachycentron canadum. The results can be summarized as follows:1. The aim of this study was to examine the effect of the compoundimmunostimulants containing β-glucan, A3a-peptidoglycan, vitamin C and vitamin E（China Patent No. ZL03112114.4.） on the growth performance, non-specific immunity andprotection against Vibrio harveyi infection in cobia （Rachycentron canadum）. Fish werefed diets containing six graded levels of compound immunostimulants (0,1,2,3,4and5gkg^-1diet) for8weeks. The results showed that the survival rate ranged from81.1%to84.4%with no significant difference among all the groups （P>0.05） after feedingexperiment. Dietary compound immunostimulants significantly increased the specificgrowth rate （SGR）, serum lysozyme, alternative complement pathway （ACP） activity,phagocytosis percentage （PP）, respiratory burst activity of head kidney macrophages ofcobia. Moreover, feeding of supplemented diets containing3.0g kg^-1compoundimmunostimulants resulted in significantly lower mortality against the pathogens, Vibrioharveyi compared with the control group. To elevate the growth and immune resistanceability of cobia, the optimal dose of dietary compound immunostimulants administration,determined by second-order polynomial regression analysis were3.43and2.71g kg^-1dietrespectively, on the basis of the SGR and mortality after challenge with V. harveyi.2. A feeding experiment was conducted to investigate the compound probioticscontaining Bacillus subtilis7.0×10⁹CFU g^-1, Bacillus licheniformis3.0×10⁹CFU g^-1,Lactobacillus spp.5.0×10⁸CFU g^-1and Arthrobacter spp.1.0×10⁸CFU g^-1on the growthperformance, non-specific immunity and protection against Vibrio harveyi infection incobia （Rachycentron canadum）. Fish were fed diets containing six graded levels of compound probiotics (0.0g kg^-1,1.0g kg^-1,2.0g kg^-1,3.0g kg^-1,4.0g kg^-1and5.0g kg^-1)for8weeks. The results showed that the survival rate ranged from81.1%to84.4%with nosignificant difference among dietary treatments （P>0.05） after feeding experiment. Dietarycompound probiotics significantly increased the specific growth rate （SGR）, serumlysozyme, alternative complement pathway （ACP） activity, phagocytosis percentage （PP）,respiratory burst activity of head kidney macrophages of cobia. Moreover, feeding ofsupplemented diets containing compound probiotics resulted in significantly lowermortality against the pathogens, Vibrio harveyi compared with the control group. Toelevate the growth and immune resistance ability of cobia, an optimal dose of dietarycompound probiotics administration, determined by second-order polynomial regressionanalysis was3.3g kg^-1, on the basis of the SGR and mortality after challenge with V.harveyi.3. The present study was performed to investigate the effects of various levels ofdietary Bacillus subtilis and chitosan on the growth performance, non-specific immunityand protection against Vibrio harveyi infection in cobia, Rachycentron canadum. Fish werefed with the control diet and six different experimental diets containing three graded levelsof B. subtilis@2×1010CFU g^-1(0.0,1.0,2.0g kg^-1diet) for each of two levels of chitosan(3.0and6.0g kg^-1diet). The results of8weeks feeding trial showed that the survival rateranged from81.3%to84.0%with no significant difference among all the groups （P>0.05）. The SGR （%） in the fish fed with dietary treatments was significantly higher thanthat of the control fish except diet group with2.0g kg^-1B. subtilis and3.0g kg^-1chitosan;significant maximum SGR was observed in the fish fed with1.0g kg^-1B. subtilis and6.0gkg^-1chitosan. The serum lysozyme activities were significantly higher in6.0g kg^-1chitosangroups than that in3.0g kg^-1chitosan groups and the control group; no significantdifferences were observed among B. subtilis levels, at the same chitosan supplementallevel. The serum ACP activities were significantly higher in3.0g kg^-1chitosan groups at0.0and1.0g kg^-1B. subtilis levels; at low chitosan level, the cobia fed diets with1.0g kg^-1B. subtilis had significantly higher serum ACP activity, but at high chitosan level, the cobiafed diets with2.0g kg^-1B. subtilis had significantly higher serum ACP activity. In thegroups with2.0g kg^-1B. subtilis regardless of chitosan levels, the phagocytosis wassignificantly increased, but the respiratory burst activity was significantly decreasedcompared with1.0g kg^-1B. subtilis. At any of three B. subtilis level, the groups with3.0gkg^-1chitosan had higher the phagocytosis and respiratory burst activity, but at2.0g kg^-1B. subtilis level, the groups with6.0g kg^-1chitosan had higher respiratory burst activity.Moreover, fish fed the diet containing2.0g kg^-1B. subtilis and6.0g kg^-1chitosan had significantly higher post-challenge survival on the7th day following Vibrio harveyiinfection and post-challenge survival showed clearly the synergistic effect of chitosan andB. subtilis. Based on these results, the combination of1.0g kg^-1B. subtilis and6.0g kg^-1chitosan is optimal for the growth, innate immunity and disease resistance of cobia with an8-week oral administration and dietary B. subtilis and chitosan should be taken intoaccount when a long term oral administration is conducted.