ARS | Publication request: Development and use of a Flavobacterium columnare challenge model in Rainbow trout

Submitted to: Annual Eastern Fish Health Workshop
Publication Type: Abstract Only
Publication Acceptance Date: March 7, 2011
Publication Date: March 28, 2011
Citation: Lafrentz, B.R., Shoemaker, C.A., Lapatra, S.E., Klesius, P.H. 2011. Development and use of a Flavobacterium columnare challenge model in Rainbow trout [abstract]. Eastern Fish Health Workshop. p. 41.

Technical Abstract: Flavobacterium columnare is a Gram-negative bacterium that causes columnaris disease in fish. Due to the economic impact of columnaris disease to the channel catfish (Ictalurus punctatus) industry, the majority of research in the United States on F. columnare involves this fish species. However, columnaris disease is also common in the rainbow trout (Oncorhynchus mykiss) industry and production of salmonids for stock enhancement. The objective of this study was to develop a laboratory challenge model for F. columnare in rainbow trout and use the model to determine the virulence of genomovar I and II isolates in rainbow trout. Six F. columnare isolates were obtained from rainbow trout experiencing losses due to columnaris disease and were ascribed to genomovar I by 16S rRNA-RFLP analysis. Three of these were chosen for a preliminary assessment of virulence and were used to challenge ten fish per isolate by immersion for 1 h in water containing the bacteria. Each isolate was virulent and induced different mortality patterns in fish following challenge. One isolate, 051-10-S5, was chosen for additional experiments to determine the ability to replicate mortality rates in independent experiments and to determine the variability between replicate groups within an experiment. In two independent experiments, using the same challenge dose and parameters, cumulative percent mortalities (CPM) were 48.9 and 49.8% and the standard errors between replicate groups were ± 7.2 and 11.1%. The challenge model was then used to compare the virulence of genomovar I and II F. columnare isolates (two isolates per genomovar) in rainbow trout. The results demonstrated a significant difference between the CPM of fish challenged with the genomovars, with the genomovar II isolates inducing higher mortality. A reproducible challenge model for columnaris disease in rainbow trout has been developed in the present study and will be useful to investigate host-pathogen interactions, vaccine development, and other control strategies.