| Summary: | 碩士 === 東吳大學 === 微生物學系 === 105 === The mariculture system of Taiwan is limited to small-scale management and intensive farming due to the available land area. Such operation has resulted in the accumulation of feed residues and aquatic metabolites as well as high breakout rates of disease in the aquaculture systems. Administration of microbial control agents is a common practice to combat diseases and subsequently induced prevalence of antibiotic resistance in the aquaculture systems has become a harsh problem that the aquaculture is facing today. In order to evaluate and analyze the effects of mariculture system on the environment, this study investigated the incidence of sulfonamide-resistant bacteria, the occurrence of resistance genes and the bacterial community structure of different mariculture systems. The rearing systems including ecological Integrated Multi-Trophic Aquaculture (IMTA) System and the traditional deep-water system of the Milkfish (Chanos chanos), the most representive farmed fish in Taiwan, were investigated. The water and sediment samples were collected from the deep-water pond, IMTA pond, and influent seawater. Samples were also collected from the giant grouper (Epinephelus lanceolatus) pond for fish species comparison. The prevalence of sulfonamide-resistant bacteria in the aquaculture environment was analyzed by the cultivation-dependent approach. The prevalence of sulfonamide-resistant bacteria of the water samples from IMTA system was significantly lower than that in of deep-water system. The sediment collected from IMTA also showed similar low resistant incidence than that of deep-water system. The isolated resistant bacteria were all gram-negative with the exception of eleven isolates from IMTA system before the Milkfish rearing. The occurrence of sulfonamide resistance gene sul1 was higher than that of sul2 in sulfonamide-resistant isolates. The presence of third resistance gene sul3 was not detected. Among all water samples, the IMTA system after Milkfish harvesting showed the lowest occurrence of resistance gene as well as resistance toward colistin sulphate, kanamycin and cephalothin. Analyzing the bacterial community by next generation sequencing revealed that Proteobacteria and Bacteroidetes were the two dominant phyla in all water samples. The bacterial community composition of IMTA system before Milkfish rearing was similar to that of IMTA after fish harvesting. The community composition of deep-water pond and giant grouper pond was rather distinct and different from the rest of water samples. The proportion of potential pathogens in the microbial community of the deep-water system was calculated to be higher than that in IMTA system. These results facilitated the understanding of the benefits and possible risks on the environments of different mariculture systems.
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