| In recent years, unreasonable stocking density, excessive fish feed and drug residues have become the prominent problems in the aquaculture of tilapia with the rapid development of intensive tilapia aquaculture in ponds. These usually caused water polluting and wasting anddisease epidemic, which have impeded the sustainable development of aquaculture. In this research, the effects of Houttuynia floating-bed on the quality of water, non-specific immunity of tilapia, and the structure and function of bacterial community for water, sediment and fish intestine were studied. The main findings are as follows:(1) During three months’ experiment from September to November, the factors of water quality, including COD, NH4+-N, NO2?-N, TP and PO43?-P in the treatment ponds were significantly lower than those of the control ponds(P<0.05), while the p H value and DO concentration fluctuated irregularly with no significant difference between the treatment and the control ponds. The activities of lysozyme(LSZ), nitric oxide(NO), alkaline phosphatase(AKP) and superoxide dismutase(SOD) of tilapia in the treatment ponds were significantly higher than those of the control ponds(P <0.05), but malondialdehyde(MDA) activity of tilapia in the treatment ponds was significantly lower than that of the control ponds(P <0.05). The average survival rate, relative weight gain and specific growth rate of tilapia in the treatment ponds(95.25%, 326.63 and 161.19, respectively) were higher than those of the control ponds(88.15%, 264.40 and 143.68, respectively), without significant difference between the treatment and the control ponds.(2) Biolog-Eco and PCR-DGGE methods were used to evaluate the bacterial community structure and function of water, sediment and fish intestine in the Houttuynia-Tilapia symbiotic system from September to November. The results showed that:① The microbial metabolic activity and bacterial diversity index of water in the treatment ponds were higher than those of the control ponds from October to November, while the status of the treatment and control ponds was opposite in September. The richness index, Shannon-Wiener index and Pielou index in the treatment ponds were higher than the control ponds during the three months. Principal component analysis(PCA) results showed the difference of carbon types utilization in the difference months. The utilization of carbon sources in control ponds was similar to treatment ponds in September, which was insignificant in October and November, and it appeared regularity of the variation in the order of September > November> October. Moreover, the Canonical Correspondence Analysis through carbon metabolism of aquatic microbial communities and environmental factors showed that ammonia nitrogen, total phosphorus, temperature and nitrates were the main influence factors to water flora. The DGGE results indicated that the microbial community of the treatment was similar to the control ponds. They belonged to seven bacterial phyla, including Actinobacteria(37.04%), Proteobacteria(33.33%), Bacteroidetes(11.11%), Firmicutes(7.41%), Chloroflexi(3.70%), Cyanobacteria(3.70%), and Fibrobacteres(3.70%). Meanwhile, Chloroflexi(strip 19) intensity in the control ponds was weaker than treatment ponds in October and November. Eight clones from fish intestine belonged to three bacterial phyla, including Firmicutes(37.50%), Proteobacteria(δ and γ subphyla)(37.50%) and Fusobacteria(25.00%).② The Biolog-Eco results showed that microbial metabolic activity and microbial diversity index of sediment in the treatment ponds were lower than the control ponds in September, while the status of the treatment and control ponds was opposite in October and November. Relative utilization ratios of carboxylic acids by microbial community were significantly different in different months, but the relative utilization ratios of other 5 categories of carbon source were similar. PCA results showed the difference of carbon types utilization in the difference months. And it appeared regularity of the variation in the order of October> November> September. The DGGE results indicated that the microbial community of the treatment and control ponds were similar, and they belonged to six bacterial phyla, including Proteobacteria(54.17%)、Bacteroidetes(16.67%)、Acidobacteria(12.50%)、Chloroflexi(8.33%)、Cyanobacteria(4.17%) and Fusobacteria(4.17%), in which Proteobacteria(54.17%) was the dominant flora. Meanwhile, Cyanobacteria(strip 3) intensity in the experimental ponds were weaker than the control pond from September to October, and in November it appeared only in the control pond samples.In summary,The Houttuynia cordata floating-bed could improve the non-specific immunity of tilapia, promote the self-cleaning function of water body, and increase the survival rate and yield of fish. On the other hand, Houttuynia floating-bed has a positive effect on maintaining the structure of microbial community,increasing the diversity of microbial community and the regulation of harmful bacteria. Therefore, Houttuynia floating-bed has good prospects in the development of tilapia aquaculture ponds. |
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