Skip to main content
ARS Home » Southeast Area » Auburn, Alabama » Aquatic Animal Health Research » Research » Publications at this Location » Publication #204393
Title: Improved husbandry to control an outbreak of rainbow trout fry syndrome caused by infection with Flavobacterium psychrophilum

Author
item Bebak, Julie
item WELCH, TIMOTHY - NAT. CTR COOL & COLDWATER
item STARLIPER, CLIFFORD - USGS NAT. FISH HLTH RES.
item BAYA, ANA - MARYLAND DEPT. OF AGRICUL
item GARNER, MICHAEL - NORTHWEST ZOOPATH

Submitted to: Journal of the American Veterinary Medical Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2007
Publication Date: 7/1/2007
Citation: Bebak, J.A., Welch, T.J., Starliper, C.E., Baya, A.M., Garner, M.M. 2007. Improved husbandry to control an outbreak of rainbow trout fry syndrome caused by infection with Flavobacterium psychrophilum. Journal of the American Veterinary Medical Association. 231: pgs. 114-116.

Interpretive Summary: A cohort of 35,200, 13-week-old, female rainbow trout at a fish farm in West Virginia was evaluated because of a two-week history of anorexia, lethargy, and a mortality rate of about 100 fish per day. Affected fish were lethargic and ataxic with bilateral exophthalmia, thin, had pale red gills and kidneys, red-tinged coelomic fluid and pale brown livers. Some were differentially pigmented bilaterally. The clinical diagnosis was bacterial or viral septicemia. The definitive diagnosis was rainbow trout fry syndrome (etiologic agent: Flavobacterium psychrophilum). The strategy for control of the outbreak was based on improving rearing conditions for the fish by reducing pathogen load in affected tanks and reducing pathogen spread among tanks. The option of treating with antibiotic-medicated feed was discussed with the farmer, but was declined. After changes were made, mortality rate declined quickly, and stopped within one to two weeks after the farm visit. Rainbow Trout Fry Syndrome (RTFS) has been extensively reported in the scientific literature as one clinical manifestation of infection with Flavobacterium psychrophilum. However, most textbooks used by aquaculture veterinarians focus on the more typical, commonly expressed form, bacterial coldwater disease. Consequently, RTFS is more prevalent that textbooks would suggest. This disease should be included on a list of differential diagnoses for septicemia in small hatchery-reared rainbow trout.

Technical Abstract: A cohort of 35,200, 13-week-old, female rainbow trout at a fish farm was evaluated because of a two-week history of anorexia, lethargy, and a mortality rate of about 100 fish per day. Affected fish were lethargic and thin and had disequilibrium, bilateral exophthalmia, pale red gills and kidneys, red-tinged coelomic fluid and pale brown livers. Some fish were differentially pigmented bilaterally. The presumptive diagnosis was bacterial or viral septicemia. The definitive diagnosis was rainbow trout fry syndrome caused by infection with Flavobacterium psychrophilum. A strategy for controlling the outbreak based on reducing pathogen numbers in affected tanks and reducing pathogen spread among tanks was developed. The option of treating with antibiotic-medicated feed was discussed with the farmer, but was declined. After changes were made, mortality rate declined quickly, with no more deaths within 10 days after the initial farm visit. Bacterial coldwater disease is the most common manifestation of infection with F. psychrophilum in fingerling and adult rainbow trout. However, the organism can also cause rainbow trout fry syndrome. This condition should be included on a list of differential diagnoses for septicemia in hatchery-reared rainbow trout fry.