Study On Effects Of Bacillus On Water Quality And Growth Performance Of Grass Carp And Its Mechanism

With the intensive development of aquiculture, water quality has been polluted seriously. The pollutants, include fish feed-stuff and aquatic animal faeces, are major compounds containing nitrogen and phosphor. These pollutants in the water can transform into harmful materials which would lead to the death of aquatic livestock and further cause huge economic losses. Application of probiotics can improve the water quality, and are rich in nutrition which can be consumed by aquatic animals. As a candidate substitute of antibiotics in aquaculture, probiotics are now well accepted and widely used in aquaculture.420 grass carps, with similar initial weight (45 g), were randomly divided into 4 groups (three replicates for each group):Control group was fed the basal diet. Treatment group 1 and 2 were fed the basal diet, and added Bacillus preparation NO 1 and NO 2 with 1×109CFU/m3 per seven days in culture water, respectively.. Treatment group 3 were fed with the basal diet added with 0.5% Bacillus preparation NO 3, and added Bacillus preparation NO 2 with 1×109CFU/m3 per seven days in culture water. Bacillus preparation NO 1 is consisted of Bacillus subtilis (without denitrifying function) and Bacillus licheniformis (4:1). Bacillus preparation NO 2 is consisted of Bacillus subtilis (with denitrifying function) and Bacillus licheniformis (4:1). The water was not exchanged during experiment period. The main research results are as follows:(1) The results of water quality determination showed that pH value were maintained between 6.8 and 7.6.Compared with the control, ammonia nitrogen content of treatment groups at the 28th day decreased by 29.17%(P＜0.05),13.18%(P <0.05) and 48.09%(P<0.01), respectively; And ammonia nitrogen content of group 1 was lower than that of group 2 by 26.71%; Nitrite nitrogen content of group 1 and 2 were below 0.39 mg/L and close to that of the control, and there were no significant differences among the three groups. But the content of group 3 was highest among four groups; Nitrate nitrogen content of group 2 and 3 were lower than that of the control, decreasing by 62.54%(P＜0.01) and 96.84%(P＜0.01) at the 21th day, respectively; Total inorganic nitrogen of four groups were all increased, and compared with the control, the values of three treatment groups decreased by 15.39%(P<0.05), 18.72%(P>0.05) and 36.31%(P＜0.01) at the 21th day, respectively.(2) The mortality of all treatment groups were significantly lower than that of control by 17.61%(P＜0.01),41.85%(P＜0.01) and 66.52%(P＜0.01), respectively, and the mortality of group 3 was lower than that of group 1 and 2 by 59.37%(P＜0.01) and 42.43%(P＜0.01).(3) Analysis of intestinal micro flora showed that compared with the control, the number of E. coli and vibrios of group 1, group 2 and group 3 decreased by 11.38%(P＜0.01) and 13.77%(P＜0.05),10.90%(P＜0.01) and 18.05%(P＜0.05), and 33.90%(P＜0.01) and 31.95%(P＜0.01), respectively, and the numbers of group 3 were lower than that of group 2 by 25.82%(P＜0.01) and 16.97%(P＜0.01), respectively. The number of Bacillus sp. increased by 43.90%(P＜0.01) compared with the control.(4) The results of immune function showed that compared with the control, the level of globulin of group 1 increased by 44.62%(P＜0.05); The level of globulin and IgM of group 3 increased by 105.43%(P＜0.01) and 36.55%(P＜0.01), which were also higher than that of group 2 by 379.24%(P<0.01) and 72.17%(P<0.01), respectively. For the nonspecific immunity index, compared with the contol, the level of C3 of group 1 increased by 45.12%(P＜0.01); The lysozyme activity, C3 content and AKP activity of treatment group 2 increased by 39.24%(P＜0.05),15.75%(P＜0.05) and 105.17%(P＜0.01), respectively; The level of MPO, C3 and AKP of group 2 increased by 24.44%(P＜0.01),100.61%(P＜0.01) and 758.53%(P＜0.01), respectively, and which were also 20.00%(P＜0.01),76.25%(P＜0.05) and 318.65% (P＜0.01) higher than that of group 2, respectively.(5) The results of antioxidative response revealed that, compared with the control, the level of SOD, ASAFR, CAT, GSH-Px and GSH of group 1 increased by 23.07%(P＜0.01),20.77%(P＜0.01),21.30%(P＜0.01),100.53%(P＜0.01) and 63.51%(P＜0.01), respectively; The level of SOD, GSH-Px and GSH of group 2 increased by 22.79%(P＜0.01),114.34%(P＜0.01) and 25.21%(P＜0.01), respectively; The level of T-AOC, GSH-Px and GSH of group 3 increased by 78.22% (P＜0.01),67.46%(P＜0.01) and 128.56%(P＜0.01), respectively, and the level of T-AOC and GSH of group 3 were higher than that of group 2 by 92.75%(P＜0.01) and 82.54%(P＜0.01), respectively.In the liver, the value of most antioxidant index for three treatment groups were higher than the control, and the level of T-AOC, SOD, ASAFR, GSH-Px and GSH for group 3 increased by 68.93%(P＜0.01),132.52%(P＜0.01),26.28%(P＜0.01),48.30% (P＜0.01) and 115.69%(P＜0.01), respectively, and SOD and CAT activty of group 3 were 30.46%(P＜0.01) and 24.77%(P＜0.01) higher than that of treatment group 2, respectively.In the serum, compared with the control, the level of T-AOC, ASAFR, ALT of group 1 increased by (P＜0.01),32.84%(P＜0.01) and 24.50%(P＜0.01), respectively; the level of T-AOC, ALT and GSH of group 3 increased by 66.58%(P＜0.01),83.00% (P＜0.01) and 80.02%(P＜0.01), respectively, and the level of ALT and GSH of group 3 were 78.36%(P＜0.01) and 200.25%(P＜0.01) higher than that of group 2, respectively. The MDA content had no significant differences among all four groups.The results indicate that Bacillus added into aquaculture water can improve water quality, reduce ammonia nitrogen, and also enhance immune function and anti-oxidation activity of grass carp. Bacillus shows better effects when added into the feed at the same time.