凡纳滨对虾工厂化循环水养殖系统水质指标及微生物菌群结构的分析

Analysis of water quality and bacterial community characterization in an industrialized recirculating aquaculture system of Litopenaeus vannamei

关键词:  凡纳滨对虾  工厂化循环水养殖  生物净化  水质指标  微生物菌群

Key words:  Litopenaeus vannamei  Industrialized circulation aquaculture  Biological purification  Water quality  Bacterial community

摘要:

为探究凡纳滨对虾(Litopenaeus vannamei)工厂化循环水养殖系统的养殖水体水质情况以及微生物菌群的组成结构，本研究利用高通量测序技术和生物信息学分析手段，测定凡纳滨对虾工厂化循环水养殖过程一级移动床生物净化、二级固定床生物净化、养殖水体的水质指标、水体和生物净化载体以及对虾肠道微生物菌群的组成。结果显示，水体的氨氮(NH4+-N)和亚硝态氮(NO2–-N)质量浓度显著降低，分别为0.85和0.21 mg/L。养殖系统水体、生物净化载体和虾肠道样品中共有的优势菌为变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)，此外，一级、二级生物净化系统水体中的放线菌门(Actinobacteria)为优势菌，生物净化载体中浮霉菌门(Planctomycetes)和硝化螺旋菌门(Nitrospirae)为优势菌；对虾肠道中的厚壁菌门(Firmicutes)为优势菌。另外，对虾养殖循环水系统中生物净化载体上的细菌物种含量比水样中的细菌物种少，但微生物多样性高于养殖水体，生物净化载体中微生物具有低丰度和高多样性的特点。综上所述，生物净化系统可有效地增加水体中促进氮、磷代谢的微生物菌群，调控养殖水体的水质指标，研究结果为凡纳滨对虾工厂化循环水养殖系统构建及水质调控提供理论依据。

Abstract:

Litopenaeus vannamei is one of the most important species of cultured shrimp in China. With the continuous development of intensive culture and increase in stocking density and feed feeding, the yield of cultured shrimp and utilization rate of the cultured environment have improved rapidly. However, a large number of residual baits, feces, fertilizers, and drugs have worsened the aquaculture water environment and led to prominent adverse environmental effects, widespread aquatic animal diseases, and severe environmental pollution. Therefore, the development of pollution-free ecological aquaculture, the promotion of industrialized circulating water aquaculture, and the research of efficient and sustainable biological purification systems have become the focus of aquaculture model research. Circulating water aquaculture is a new aquaculture mode in which water is treated and reused using modern techniques. To explore aquaculture water quality and the composition structure of microbial flora in an industrialized circulating water aquaculture system of L. vannamei, the water quality indexes of biological purification aquaculture systems such as primary moving bed biological purification, secondary fixed-bed biological purification, and aquaculture water, and the microbial flora of water and shrimp intestines were measured using high-throughput sequencing technology and bioinformatics analysis. The experimental results showed that the mass concentrations of ammonia nitrogen (NH4+-N) and nitrite nitrogen (NO2–-N) in the culture water met the standards for the healthy culture of L. vannamei after treatment with the biological purification culture system. Concentrations are 0.85 and 0.21 mg/L. Results showed that all water and carrier samples contained a certain abundance of nitrifying Spirillum bacteria, especially on the biological purification carrier, which was significantly higher than the proportion of the bacterial community in water samples. The Chao1 and Shannon indices of chemical fiber filament biological carriers were significantly higher than those in shrimp intestines. Results also showed that the number of microbial species and microbial community diversity on the biological carrier of chemical fiber filaments were higher than those in the intestine of shrimp. The bacterial community composition was characterized at the phylum and genus levels. A total of 46 bacterial phyla were identified in the samples. Proteobacteria, Bacteroidetes, and Actinobacteria were the dominant phyla in the water, and Proteobacteria, Bacteroidetes, Actinobacteria, and Planctomycetes were the dominant phyla in the biological carrier; Proteobacteria, Bacteroidetes, and Firmicutes were the dominant phyla in the shrimp intestine. The abundance of Planctomycetes in the biological carriers increased. The abundance of Proteobacteria and Firmicutes in shrimp intestines was higher than that in water, conducive to the degradation of nitrogen and phosphorus. Bacteroidetes and Firmicutes were the main metabolizing bacteria in the intestine, promoting carbohydrate metabolism and energy acquisition in shrimp. Actinobacteria can degrade organics, including macromolecules such as starch and proteins, and produce antibiotics and other antibacterial substances. The abundance of Actinobacteria in water was very high but decreased in shrimp, which played an important role in the decomposition of organic matter and nitrogen in water. The bacterial species content in the biological purification carrier of the shrimp culture circulating system was lower than that in the water sample, but the microbial diversity was higher than that of aquaculture water. The microorganisms in the biological purification carrier have the characteristics of low abundance and high diversity, possibly due to the increase in the abundance of environment-related functional bacteria on the biological purification carrier and the decrease in some flora species with little impact on the environment, resulting in the aggregation of biofilm bacteria species. In addition, the water and biological purification carrier also contained a certain amount of pathogenic bacteria, such as Vibrio and Mycobacterium. Therefore, it was necessary to regulate the content of pathogenic bacteria in the water environment and shrimp intestine to ensure a healthy shrimp culture. The results showed that the multi-stage biological purification system can effectively increase the microbial flora, promote the metabolism of nitrogen and phosphorus in the water, and regulate the quality of the aquaculture water. The dominant bacterial groups in water, biological purification carriers, and shrimp were different. Proteobacteria and Bacteroidetes were dominant in water biological carriers and intestines, whereas Planctomycetes mainly exist as biological carriers, Firmicutes mainly colonize the intestine, and Actinomycetes mainly exist in water. In this study, high-throughput sequencing technology was used to study the composition of the microbial community structure in the circulating water culture system of L. vannamei. Results can reveal the diversity of its internal microbial community, provide a basis for further revealing the "black box" of biofilters, and have important guiding significance for the study of the construction and denitrification efficiency of biofilters in seawater circulating water culture.