| Grass carp is one of the major breeding in freshwater, occupies very important position in aquaculture. Along with the development of grass carp aquaculture industry modernization and intensive degree, high density cultivation mode makes single breeding environment ecosystem structure, weak resistance; At the same time, a large number of the bait and fish waste get into the water in the breeding process, easy cause eutrophication of water. In recent years, the substrate has become a research direction to solve these problems. The team will this technology applied in grass carp aquaculture, the substrate can significantly improve the grass carp growth performance and nonspecific immune function, and changes the bacterial community composition. But at present most scholars study the substrate what are concentrated in the effect of its application in aquaculture and feasibility, rarely studied considering the carrier material cost. Therefore, this paper focuses on the above problem we designed the following experiment content: 1) Effects of the density of substrates on the growth of grass carp, metabolism, water quality and microbial activities. To study the effect of density of substrates on grass carp growth performance and serum enzyme activity. According to the substrare surface area of cement water surface area ratio(specific surface area), test is divided into 50%(S-50), 100%(S-100), 150%(S-150) and the control group(no substrate). The results showed that the weight gain rate and specific growth of grass carp in S-100 and S-150 treatment group had no significant difference, but were significantly higher than control group and S-50 group(P<0.05), feed conversion rate were significantly lower than control group(P<0.05), S-100 treatment group had a significantly higher survival rate for other groups(P<0.05). COD content in S-100 treatment group was significantly lower than control group(P<0.05), dry matter(DM) content of fouling organisms and biomass(VSS) in S-100 treatment group is significantly higher than other treatment group(P<0.05). The catalase(CAT) activity is no significant difference(P>0.05) between S-100 and S-150 group, were significantly lower than the control group and S-50 group(P<0.05); the superoxide dismutase(SOD) activity in S-150 treatment group was significantly lower than the control group and S-50 treatment group(P<0.05), but there were no significant differences between S-100 and S-150 treatment group(P>0.05); the aspertate amino acid transaminase(AST) activity in experimental groups was significantly lower than control group(P<0.05). The research results show that the density of substrates influence the growth of grass carp and serum enzyme activity, more than 100% the density of substrates may promote the balance of active oxygen free radical metabolism of grass carp, strengthen the antioxidant ability. Under this experimental condition, when set up the substrate surface area of water surface area ratio(surface) 100%, not only can significantly promote the growth of grass carp,but also improve farming production, reduce the bait coefficient, and effectively reduce the production cost. 2) In different C/N ratio conditions, affecting the ecological growth performance, water quality and microbial activities of grass carp. To investigate the effect of C/N ratio and substrate integration on water quality, microbial dynamics and growth of Ctenopharyngodon idellus, bacteria community composition of substrate and water bacterial community composition at four C/N ratios was investigated by using PCRdenaturing gradient gel electrophoresis(DGGE) technique. The aquaculture water quality, growth performance of C. idellus were also investigated. An artificially formulated and prepared feed containing 30% crude protein was applied to all ponds.In order to raise the C/N ratio of aquaculture water to 15:1(CN15),20:1(CN20) and 25:1(CN25),glucose was applied separately as a source of carbohydrate in addition to artificial feed.The results showed that weight gain and specific growth rate of grass carp in CN20 treatment group were significantly higher(P < 0.05) than other groups, feed conversion ratio in CN20 group was lower than other groups(P < 0.05). Dissolved oxygen, ammonia and nitrite concentration in CN25 group were significantly lower(P < 0.05) than other groups, COD and BOD in CN25 group was higher than other groups(P < 0.05). The amount of bacteria in substrate gradually increased with the increasing of C/N ratio, and peaked at 5.57×107cells/g. With the increasing of C/N ratio, bacterial community composition similarity of aquaculture water in the control group andCN15, CN20, and CN25 treatment group with that of source water was 37%, 32%, 26% and 22% respectively; Bacterial community composition similarity between substrate and water was 59%, 58%, 55% and 52% respectively. Rhodobacter blasticus and Chloroflexi, the common bacteria in substrates, existed only in water of control group and CN15 treatment group. Bacteroidetes was dominant bacteria in both water and substrate of CN20 treatment group. The results demonstrated that C/N ratio affects bacterial migration from water to substrate. The C/N ratio of 20:1 and substrate can significantly promote the growth of C. idellus and improve aquaculture production. These results will provide a scientific basis for the further application of substrate in the actual production of C. idellus.This study optimize the application of substrate in grass carp for the first time, when hung the substrate surface area account for 100% of the pond water surface area ratio, substrate can significantly promote the growth of grass carp, and improve farming production, reduce the bait coefficient, and can effectively reduce the production cost; At the same time, substrate and C/N control play a role of the edge can be used in combination, the effect of using the C/N control(20:1)in the ecological grass carp pond is best, can purify the water quality, also can increase production. |
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