In-situ pretreatment of aquaculture tail water by molasses addition and the responses of bacterioplankton communities

Abstract

To reduce the pollutant concentrations in aquaculture tail water before discharging is important. Microcosmic experiment on pond culture of tilapia was conducted, in-situ molasses addition before 58 days of harvest was performed, and its effects on quality of aquaculture tail water and the responses of bacterioplankton communities were detected. Our findings showed that the molasses addition effectively reduced the concentration of total phosphorus, total nitrogen, and three kinds of inorganic nitrogen in aquaculture tail water. And its linear effect on nitrate and nitrite nitrogen was through the impact on the bacterioplankton communities.The dominant bacteria observed were Proteobacteria and Bacteroidetes, indicating that water quality physicochemical parameters have a significant correlation with different bacterial communities. FAPROTAX software provided bacterial function predictions and identified chemoheterotrophic bacteria as dominant in the tail water. In addition, abundance of functional microorganisms associated with nitrogen and phosphorus cycling was high. Interestingly, the growth-promoting effect of molasses on cultured organisms may not be due to the ingestion of biofloc by animals but could be a direct effect of molasses.Our study demonstrates that the addition of molasses can improve the quality of cultured tail water, reduce the environmental purification pressure, significantly alter microbial community structure in the water, enhance the nitrogen cycling capacity of the aquatic environment, and promote the growth of cultured animals. These results can provide a theoretical basis for the application of molasses in in-situ pretreatment of aquaculture tail water.