| The development of intensive aquaculture industry has led to the deterioration of water environment and frequent occurrence of aquatic animals' diseases, which affect the growth, and even cause death of aquatic animals. Probiotics can not only promote the growth and prevent the diseases of aquatic animals, but also play a crucial role in improving water quality. The present study was conducted to study the effects of Bacillus on the growth performance, intestinal digestive enzyme activities, intestinal flora composition, immunity and antioxidant capacity of grass carp, and also to study its effect on water quality.In this study,450 grass carps with about initial weight (45 g) were randomly divided into 3 groups (three eplicates for each group,50 fish per eplicate):Control group was fed the basal diet. Group 1 were fed the basal diet added 0.1% Bacillus complex (B. subtilis and B. amyloliquefaciens,1:1). Group 2 were fed the basal diet added 0.1% B. subtilis. Three groups were fed with feed (2% fish weight) at 8:00, 12:00 and 21:00 everyday. The test lasted for 45d and the water was changed 1/3 every week. Main research results are as follows:(1) Water quality determination showed that, compared with the control, nitrite nitrogen in water of group 1 and 2 significantly decreased from the 21d th to the end of the experiment (except the 35d th of group 1, P＜0.01); and ammonium nitrogen of group 2 also significantly decreased at 21d th and 35d th. There were no significant differences in nitrate nitrogen and pH among the three groups.(2) Feeding experiment showed that, compared with the control, ADG of group 1 and group 2 increased by 50.00% (P<0.01) and 20.00% (P<0.05), respectively; ADFI of group 1 and group 2 increased by 44.44% (P<0.01) and 16.67% (P<0.05), respectively; compared with group 2, addition of complex Bacillus increased both ADG and ADFI significantly (25.00% and 23.81%, respectively, (P<0.01)). It also revealed that compared with the control, addition of Bacillus to the feed decreased the death rate of grass carp.(3) Digestive enzyme activities determination revealed that, in the intestine, compared with the control, trypsin activity of group 1 increased by 79.46% (P<0.01), and trypsin, lipase and amylase activities of group 2 increased by 14.75% (P<0.01), 13.03% (P<0.01) and 78.95% (P<0.01), respectively. In the hepatopancrea, compared with the control, lipase activity of group 1 increased by 16.82% (P<0.01), but the trypsin and amylase activities were not significantly affected, and lipase and trypsin activities of group 2 increased by 17.72% (P<0.01) and 13.81% (P<0.01), respectively.(4) Analysis of intestinal microflora showed that, compared with the control, the number of Bacillus sp. in the intestine of group 1 and 2 increased by 21.51% (P<0.01) and 23.51% (P<0.01), respectively, and the number of E. coli decreased by 13.46% (P<0.01) and 14.23% (P<0.01), and the number of vibrios decreased by 16.99% (P<0.01) and 16.85% (P<0.01). Bacillus had no significant effects on the number of total aerobic bacteria, lactic acid bacteria and seudomonas sp.(5) Determination of serum immune parameters showed that, Bacillus had no significant effect on serum total protein, globulin and albumin levels, A/G ratio and lysozyme activity of grass carp. Compared with the control, IgM, C3 and AKP of group 1 increased by 30.77% (P<0.01),34.62% (P<0.01) and 107.79% (P<0.01); similarly, and group 2 increased by 100.00% (P<0.01),123.08% (P<0.01) and 108.87% (P<0.01). Bacillus had no significant effects on GOT, GPT and the myeloperoxidase activities of grass carp.(6) Antioxidant parameters assay revealed that, compared with the control, levels of serum SOD, GSH, T-AOC and GSH-Px of group 1 increased by 20.06% (P<0.01), 32.76% (P<0.01),41.75% (P<0.01) and 11.30% (P<0.05), respectively, and levels of CAT, SOD and GSH-Px in intestinal mucosa increased by 41.44% (P<0.01),38.01% (P<0.01) and 19.56% (P<0.01), respectively, levels of hepatopancrea SOD and GSH increased by 33.83% (P<0.01) and 25.86% (P<0.01), respectively. Compared with the control, levels of serum T-AOC, CAT and SOD of group 2 increased by 18.31% (P<0.01),44.23% (P<0.05) and 11.01% (P<0.01), respectively, levels of CAT, SOD, GSH and ASAFR in intestinal mucosa increased by 17.12% (P<0.01),63.89% (P<0.01),70.92% (P<0.01) and 15.69% (P<0.05), respectively, levels of hepatopancrea T-AOC, CAT, SOD and GSH increased by 37.60% (P<0.01),52.00% (P<0.01),39.05% (P<0.01) and 51.39% (P<0.01), respectively. Compared with the control, level of MDA in serum and hepatopancrea of group 1 decreased by 6.21% (P<0.05) and 25.39% (P<0.01), respectively, group 2 decreased by 48.62% (P<0.01) and 12.62%(P<0.01), respectively.In conclusion, Bacillus added in basal diets can improve the growth performance and decrease the death rate of grass carp, and this may be due to increased digestive enzyme activities, improved intestinal flora composition, and enhanced immune function and antioxidation capacity. It was also revealed that Bacillus complex showed better growth-promoting effect than B. subtilis. |
