An alternative-protein diet does not impact microbial stability in salmon Recirculating Aquaculture Systems

Victor Schmidt*, Christopher Good, Linda Amaral-Zettler
 
*Department of Ecology and Evolutionary Biology, Brown University. Providence, RI.
Josephine Bay Paul Center for Comparative Molecular Biology and Evolution, Marine Biological Laboratory. Woods Hole, MA.

Among the chief economic and environmental concerns in aquaculture is a reliance on fishmeal as the traditional protein source. Fishmeal based feeds often require harvest from wild fish stocks and fishmeal prices can fluctuate widely, having increased dramatically over the last decade. Significant advances have therefore been made in alternative diet formulations. Although the impact of these alternative diets on the fish itself has been the subject of recent research, including fish performance, intestinal inflammation, palatability, and gut microbiota, less research has been conducted on how alternative feeds impact the aquaculture environment as a whole. Recently, the implementation of Recirculating Aquaculture Systems (RAS) using closed containment technology has highlighted the need to maintain stable environmental and microbiological conditions within a farm environment. Microbial stability in RAS biofilters is particularly important, given their role in nutrient processing and water quality. If and how the impacts of alternative feeds on the microbial communities in fish translate into changes to the biofilters is not known. We tested the influence of a fishmeal free diet on the microbial communities in RAS water, biofilters and salmon microbiomes using high-throughput 16S rRNA gene amplicon sequencing. Salmon were grown to market size in six replicate RAS tanks, three with traditional fishmeal diets and three with alternative fishmeal-free diets. Samples were taken from adult market-ready intestines and gills, and from water and biofilters in each corresponding RAS unit. Our results corroborate previous findings that diet has a clear influence on microbiome structure of the salmon intestine, but extends these results to provide the first data on how the RAS environment as a whole is influenced by feed type. Our results show strong stability of taxa likely involved in water quality processing (e.g. Nitrospira) regardless of diet, and may further alleviate concerns regarding the use of alternative feeds in RAS operations.