DIQUAT AND COLUMNARIS DISEASE NEW ANIMAL DRUG RESEARCH AND STATUS.  

J. Alan Johnson*, Stephen Grausgruber, Randall Esser, Jim Bowker, and Molly Bowman
 
Iowa Department of Natural Resources
Rathbun Fish Culture Research Facility
15053 Hatchery Place
Moravia, IA 52544
alan.johnson@dnr.iowa.gov

Use of Diquat dibromide (REWARD ® Herbicide; Syngenta) to control mortality of fish due to  Flavobacterium sp. infections was first reported by Bullock et al. (1990) and has been available for investigational purposes under the U. S. Fish and Wildlife Service (FWS) Investigation New Animal Drug (INAD) exemption since the early 2000's. Because Diquat does not have an active sponsor,there has been limited research toward a U. S. Food and Drug Administration approval.. Recently, the FWS Aquatic Animal Drug Approval Partnership (AADAP) Program developed a drug research plan for Diquat including trying to find a sponsor t to lead the approval effort for this drug. In 2016, researchers with the Iowa Department of Natural Resources and AADAP conducted a trial at Rathbun Fish Culture Research Facility to contribute to the Diquat drug approval.

Walleye fingerlings (116 mm, 12.1 g) held in a 1457 L raceway displayed skin lesions consistent with infection of F. columnare bacteria. Low fish mortality indicated the disease was in the initial stage of infection. Fish were transferred into eight test tanks (93.9 L; 85 fish/tank) and tanks were randomly designated as treated or control (N=4). Treated tanks received 18 mg/L Diquat dibromide for two hour static bath treatment on three consecutive days whereas control tanks received a static bath sham water treatment for the same duration and frequency. Fish mortality was documented for 14 d posttreatment, and at the end of the study, mean percent cumulative mortality in treated tanks (6.6%) was significantly different (P=0.0376) than that in control tanks (38.8%).