The Fate of Bacteriophages in Recirculating Aquaculture Systems (RAS)—Towards Developing Phage Therapy for RAS

Gabriel M.F Almeida,Lotta-Riina Sundberg,Jouni Vielma,Kati Mäkelä,Jani Pulkkinen,Elina Laanto

doi:10.3390/antibiotics8040192

Abstract

Aquaculture production has increased tremendously during the last decades, and new techniques have been developed, e.g., recirculating aquaculture systems (RAS). In RAS, the majority of water volume is circulated via mechanical and biological filters and reused in the tanks. However, the prevention and treatment of diseases in these systems are challenging, as the pathogens spread throughout the system, and the addition of chemicals and antibiotics disrupts the microbiome of the biofilters. The increasing antibiotic resistance has made phage therapy a relevant alternative for antibiotics in food production. Indeed, as host-specific and self-replicating agent they might be optimal for targeted pathogen eradication in RAS. We tested the survival and spread of Flavobacterium columnare -infecting phage FCL-2 in recirculating aquaculture fish farm with rainbow trout (Oncorhynchus mykiss) in a fully controlled study. After a single addition, phage persisted in water samples collected from tank, fixed bed, moving bed, and aeration unit up to 14 days, and in the water of rearing tanks, rainbow trout mucus, and bioreactor carrier media from the fixed and moving bed biofilters for 21 days. Furthermore, phage adsorbed preferentially to moving bed carrier media, which contained biofilm attached and from which higher phage numbers were recovered. This study shows phages as a potent strategy for maintaining biosecurity in RAS systems.

Highlights

Aquaculture production is an important source of a protein destined for human consumption.It is an expanding industry with many strategies employed to improve efficiency and environmental impact
Phages were recovered from all sampled components of the recirculating aquaculture systems (RAS) system up to 14 days, and from the water from rearing tanks, fish mucus and carrier media from the fixed and moving bed biofilters for 21 days after a single phage exposure (Figure 1A–G)
Phage titers were higher in filter carrier media samples, suggesting that bacterial biofilm may have a role in phage enrichment

Summary

Introduction

Aquaculture production is an important source of a protein destined for human consumption. It is an expanding industry with many strategies employed to improve efficiency and environmental impact. Water in RAS is reused after being treated, dramatically reducing the amount of water needed for fish farming in aquaculture sites. Confining large populations of aquatic animals are a risk factor when considering infectious diseases, and aquaculture rearing units have been shown to favor pathogens and virulence increase [3,4,5]. The reuse of water in RAS may pose a biosecurity challenge for infectious diseases, as the removal of pathogens or chemical residues from the tanks is difficult, increasing the unnecessary exposure of aquatic animals to both [6].

Methods

Results

Discussion

Conclusion