Microbial Diversity in Bio-Filter of the Recirculating Aquaculture System for Litopenaeus vannamei

Abstract:

In order to study the biodiversity of microbial community structure and explore the water quality purification mechanism of bio-filter in the recirculating aquaculture system for Litopenaeus vannamei, microorganism samples were collected from 5 different positions which were the outer and inner surfaces of the upper part of nano-membrane, the outer and inner surfaces of the lower part of the nano-membrane, and the collecting tray. Microbial diversity, functional microorganisms and purifying capacity among different samples were analyzed according to molecular biological methods and 16S rRNA gene pyro sequencing. The results showed that 10 phyla were identified in 5 different positions, in which Proteobacteria was the dominant group. Nitrospirae was detected in the nano-membrane (4.3%), while with low abundance in the collecting tray (0.33%). Ammonia oxidizing bacteria and nitrite oxidizing bacteria in nano-membrane were the primary microorganisms to remove nitrogen and the proportions were 1.70% and 6.99%, respectively. There were 41 dominant species identified in total. Among which, Pedobacter was absolutely dominant, Parvularcula was the second dominant species, and both abundance ratios were above 10%. Nitrospira was the third dominant species, whose average abundance on membrane (4.31%) was significantly higher than that in the collecting tray (0.28%). Rich biodiversity of microorganism and stable microorganism ecosystem in the biological filter had a crucial role in buffering water quality. The analysis of effective biomass indicated that nitrification happened mostly in the upper part of the biological filter, and the nitrification effect was weakened in the lower part, while almost disappeared in the collecting tray. Therefore, in order to improve efficiency of nitrification, the hanging membrane density and length should be scientifically designed and rationally distributed.