Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/2/2014
Publication Date: 10/30/2014
Citation: Straus, D.L., Farmer, B.D., Beck, B.H., Bosworth, B.G., Torrans, E.L., Tucker, C.S. 2014. Water hardness influences Flavobacterium columnare pathogenesis in channel catfish. Aquaculture. 435:252-256.
Interpretive Summary: Columnaris disease in fish is caused by bacteria and is the most important cause of mortality in aquaculture. It can affect any freshwater fish throughout the world. We set up a study to determine why we could easily reproduce the disease by exposing catfish to the bacteria in well water at our research center in Stuttgart, Arkansas but our colleagues in Stoneville, Mississippi could not in their well water. In the first experiment, all fish exposed to a dose of the bacteria in our water died, but none of the fish exposed to the same dose of bacteria in their water died. We used an analytical technique to determine that 1900-times more bacteria attached to fish gills in our water versus their water. The second experiment showed that filtering our water with a water softener to remove hardness, or filtering their water with a charcoal filter to remove tannins (which were believed to inhibit bacteria), indicated that hardness was the key factor influencing the mechanism of fish getting columnaris disease.
Technical Abstract: Studies were conducted to determine aspects of water chemistry responsible for large differences in pathogenesis and mortality rates in challenges of channel catfish Ictalurus punctatus with Flavobacterium columnare; challenges were conducted in water supplying the Stuttgart National Aquaculture Research Center (SNARC; Stuttgart, Arkansas), and the Warmwater Aquaculture Research Unit (WARU; Stoneville, Mississippi). Waters differed in two major characteristics: compared to SNARC water, WARU water contained appreciable dissolved organic matter (DOM) and low concentrations of dissolved calcium and magnesium. In Experiment 1, fish were challenged with F. columnare in aquaria with either SNARC or WARU water. Mortality at 4 d was 100% in SNARC water, while no fish died in WARU water. Bacterial adhesion to gill surfaces also differed dramatically and was approximately 1900-times higher for fish challenged in SNARC water (more than 800,000 bacterial CFUs/ng extracted DNA) than in WARU water (fewer than 450 CFUs/ng). Experiment 2 was conducted with a lower bacterial challenge to determine which factor, DOM or divalent cation concentration, caused this difference. Complete removal of DOM from WARU water by carbon filtration did not affect bacterial adhesion to gills or result in greater mortality in challenged fish. Consequently, DOM did not contribute to the differences in mortality seen in Experiment 1. However, removal of most calcium and magnesium from SNARC water by ion-exchange filtration resulted in decreased bacterial adhesion to gill and decreased mortality compared to un-altered SNARC water. It appears that the concentration of divalent cations (hardness) affects pathogenesis of columnaris disease.