Management of coldwater disease caused by Flavobacterium psychrophilum on Ontario trout farms
Coldwater disease caused by Flavobacterium psychrophilum is the primary disease of concern for raceway operations that use groundwater. Commercial vaccines are not available for coldwater disease and management, including antimicrobial use, is critical. A longer-term plan of the Fish Pathology Laboratory (FPL) is to conduct autogenous vaccine trials for coldwater disease. To increase the likelihood that this strategy will be effective however, several pieces of information are still needed including; a) further characterization of Ontario F. psychrophilum strains and b) characterization of the growth conditions required for optimum expression of virulence/immunogenic proteins and effective production monitoring systems to ensure that improved performance can be evaluated.
From work done to date in 2008 we have investigated one ‘outbreak' of coldwater disease that is systemic and affected fish have no external ulcerative disease (typical tail rot or necrotic myositis). This systemic form of coldwater disease during the early stages of production appears to be the rule rather than the exception. This is scientifically novel (although it is not to the farmer) and has received little concerted attention. This form of coldwater disease is particularly important to study as there are virtually no macroscopic lesions visible in affected fish, although mortality may increase and there are detectable but initially subtle, clinical signs. Monitoring of these early signs, along with lesions present using light microscopy is part of the ongoing project. Work in ongoing to characterize the isolates already obtained however further collection of strains is needed. Dozens of isolates from multiple clinical episodes are needed to derive conclusions about strain patterns, etc. This is the first objective for the present project.
There a single published study using two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) to determine the proteome of F. psychrophilum (Sudheesh et al. 2007). We have been using this rather exacting and laborious ‘search' tool for comparison of culture conditions that influence protein expression of F. psychrophilum. We have identified several proteins that are strong candidates and need to screen larger numbers of strains. The second objective of this proposal is to raise antisera to these proteins of interest. Lastly the final objective of this proposal is to undertake a treatment trial to determine the efficacy of florfenicol as a therapeutic measure to blunt the impact of coldwater disease. This trial is outlined in the report appended. Florfenicol is used to treat outbreaks of coldwater disease and appears to be effective in the short term. What is not known is if treatment in early stages (<1g) can produce long-term improvements in fish health and farm productivity.
2007 - 2009
Central Canada: Great Lakes, St. Lawrence Freshwater Drainage Basin
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