Drug Research Information Bulletin - Efficacy of Chloramine-T to Control Mortality Due to a Natural Infection of External Columnaris Disease Flavobacterium columnare in Juvenile Late Fall Chinook Salmon Oncorhynchus tshawytscha

Columnaris disease (causative agent, Flavobacterium columnare) is an acute-to-chronic bacterial infection with a worldwide distribution capable of infecting most freshwater fishes (Noga 2000). The disease most commonly occurs as an external infection; however, it can also occur as a systemic infection with no visible external signs (Post 1987). Flavobacterium columnare is more pathogenic at temperatures >15oC, and both mortality and acuteness of disease increase with temperature (Post 1987; Noga 2000). Typically, an external columnaris outbreak requires intervention (e.g., improving water quality or fish culture conditions and/or using chemotherapeutants) to reduce the bacterial load on fish. Several chemotherapeutants have historically been used to control mortality caused by external columnaris, and chloramine-T (CLT) is generally regarded as one of the most effective. Based in part by research conducted by AADAP (Bowker et al. 2008; Bowker et al. 2011; Bowker et al. 2013), Halamid® Aqua (100% CLT; sponsor, Axcentive SARL, Bouc Bel Air, France) was approved in May 2014 by the U.S. Food and Drug Administration (FDA) to control mortality in freshwater salmonids due to bacterial gill disease. The label (i.e., approval) was then expanded to control mortality due to external columnaris in walleye Sander vitreus and warmwater finfish. To further expand the existing label to allow use to control mortality in all freshwater finfish due to columnaris, an additional field effectiveness study was required on a coldwater fish species.

In this bulletin, we summarize the results of a study conducted to demonstrate the effectiveness of CLT to control mortality in late fall Chinook Salmon (CS) Oncorhynchus tshawytscha fingerlings naturally infected with external columnaris disease.