Exploring the Use of Ultraviolet (UV) Irradiation to Reduce the Risk of Flavobacterial Disease Outbreaks in Hatcheries and Aquaculture Facilities

1,2Christopher K. Knupp, 1Mohamed Faisal, 3Benjamin R. LaFrentz, 4Matt J. Griffin,

5Esteban Soto, 6Gregory D. Wiens, 1,2,7Thomas P. Loch

1Michigan State University - Aquatic Animal Health Laboratory, Aquatic Animal Disease Ecology Program, East Lansing, MI; 2Department of Fisheries and Wildlife, College of Agriculture and Natural Resources, Michigan State University, East Lansing, MI; 3Aquatic Animal Health Research Unit, United States Department of Agriculture – Agricultural Research Service, Auburn, AL; 4Thad Cochran national Warmwater Aquaculture Center, Delta Research and Extension Center, Mississippi State University, Stoneville, MS; 5Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, Davis, CA; 6National Center for Cool and Cold Water Aquaculture Research Service, United States Department of Agriculture – Agricultural Research Service, Kearneysville, WV; 7Department of Pathobiology and Diagnostic Investigation, College of Veterinary Medicine, Michigan State University, East Lansing, MI

ABSTRACT

According to the Food and Agriculture Organization of the United Nations, fish-pathogenic flavobacteria (Family Flavobacteriaceae) are leading causes of disease-related losses in aquaculture facilities, globally.  Compounding the issue, efficacious vaccines are currently unavailable and reports of antimicrobial resistance among flavobacteria are increasing, highlighting the need for alternative prevention methods.  Ultraviolet (UV) irradiation of facility source water is an effective means of reducing the risk of disease outbreaks caused by other fish pathogens; however, the UV dose required to inactivate the diversity of flavobacteria associated with diseases in fish has been inadequately studied.  To eventually arm aquaculture personnel with a tool to enhance facility biosecurity and reduce the risk of flavobacterial epizootics without the use of chemotherapeutants, a series of experiments were designed to identify UV doses capable of substantially reducing viable flavobacteria. Sixty-five flavobacterial isolates (n=36 species) recovered from diseased fish or their hatchery environments, including multiple geographically widespread Flavobacterium psychrophilum (causative agent of bacterial coldwater disease) and F. columnare (etiological agent of columnaris disease) variants, were assayed for their ability to survive a low dose (LD; 25mW/cm2) and high dose (HD; 125mW/cm2) of UV radiation using a collimating beam apparatus.  At the LD, most (49/65) flavobacterial isolates were reduced by >99%, whereas the remainder were reduced by 32-98%.  At the HD, 63/65 flavobacterial isolates were reduced by >99%, whereas the two remaining isolates were reduced by 98.6-98.9%.  Notably, some F. psychrophilum and F. columnare variants appeared less susceptible to UV irradiation, whereby reduction at the LD and HD ranged from 32-100% and 98-100% for F. psychrophilum and from 95-100% and 98-100% for F. columnare.  Overall, study results demonstrate that viable flavobacterial loads are substantially reduced at a UV radiation dose of 125mW/cm2 under laboratory conditions, indicating that UV radiation is promising in minimizing flavobacteria load in hatcheries and aquaculture facilities.