Title : Algal biofilter treatment of fish pathogens in recirculating aquaculture systems
Abstract:
Integrated multi-trophic aquaculture recirculating aquaculture systems (IMTA-RAS) are proven to be great for the sustainable production of fish while conserving water and recycling nutrients. Fish pathogens are a significant cause of loss and cost in aquaculture. Frequently, pathogens accumulate in high nutrient areas such as in the microbial community of the nitrifying biofilter in the IMTA-RAS. On the other hand, algal biofilms can enhance the disease resistance and growth of the cultured species and increase water quality. Previous research at Mote shows that microbial communities of periphyton (algae, bacteria, and archaea in an attached submerged biofilm) may help to reduce the number of pathogens in the IMTA-RAS, preventing their establishment in biofilms. Validation of the effect of biofilter combination is necessary to establish where pathogens are residing within the IMTA-RAS and if periphyton is useful for remediating fish pathogens. Two trials were carried out on two separate 2500 L pilot scale IMTA-RAS for different biofilter combinations with samples taken over two different time periods per trial. The combinations tested in trials were periphyton only and periphyton in combination with a nitrifying biofilter. Samples were extracted with Qiagen EarthSoil Kits and validated on a Nanopore Nanodrop. High resolution classification of fish pathogens using the hsp70 gene and next generation sequencing was carried out to precisely examine fish pathogens in periphyton biofilters and nitrifying biofilters. Results will be compiled by OTU and into stacked bar charts, then compared for significant differences. The results indicated significant differences between the Vibrio communities in the MBBR and periphyton biofilter with up to a 90% lower population in the periphyton. Additionally, communities of Pseudomonas and Mycobacterium showed a lower population count in the periphyton biofilter. The results may be explained by the microbial ecology relating different clades such as archaea, Vibrios, nitrogen cyclers, and Cyanobacteria. Total population of pathogens in the MBBR was 3107 ± 518 versus total pathogen population of 427 ± 149. The microbial shift in the biofilter may be explained by microbial ecology and survival strategy (e.g. commensalism, parasitism, opportunism, etc.) differences between biofilter types. Although the results are promising, the microbial community needs to be correlated to removal of pathogens in the water column as well as operational and environmental conditions. Paired with biosecurity measures, IMTA-RAS biofilters provide a resilient, adaptable, and strong fortification for fish health.
