Title: Evaluation of Diquat against an acute experimental infection of Flavobacterium columnare in channel catfish, Ictalurus punctatus Authors
Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 25, 2008
Publication Date: May 6, 2009
Citation: Darwish, A.M., Mitchell, A.J. 2009. Evaluation of Diquat against an acute experimental infection of Flavobacterium columnare in channel catfish, Ictalurus punctatus. Journal of Fish Diseases. 32:401-408. Interpretive Summary: Columnaris disease, caused by the bacterium Flavobacterium columnare, exists worldwide and affects a wide variety of fish. In the United States, columnaris is one of the two most costly diseases to the channel catfish industry. Because of the serious losses attributed to the disease, therapeutants are needed to control columnaris. The present study was designed to assess the therapeutic potential of diquat (6,7-Dihydrodipyrido[1,2-a:2',1'-c]pyrazinediium dibromide) against an acute columnaris infection. The results demonstrated that one application of diquat at 5 mg/L or higher concentration will significantly reduce mortalities of acutely infected fish. The results also demonstrated that diquat will have more practical applications in tanks rather than ponds. Further research will be warranted to optimize the dose concentration and the application frequency and duration.
Technical Abstract: A trial was performed to evaluate the efficacy of diquat (6,7-Dihydrodipyrido[1,2-a:2',1'-c]pyrazinediium dibromide) against an acute experimental infection of Flavobacterium columnare in channel catfish, Ictalurus punctatus. Diquat is an Environmental Protection Agency-approved herbicide and has the potential to be legally and practically used against columnaris. Channel catfish were challenged, by cutaneous abrasion and waterborne exposure to F. columnare, and treated once at 22 h post challenge with 2.5, 5.0, 10.0 and 15 mg L-1 of diquat active ingredient for 6 h. At the conclusion of the trial, 21 d post challenge, diquat at 5.0, 10.0 and 15 mg L-1 significantly (P<0.05) reduced the mortality of infected fish from 95 % in the challenged non-treated fish to 68, 59 and 49 %, respectively. In vitro, the minimum inhibitory concentration (MIC) of 23 isolates of F. columnare was assayed. The majority of the isolates had an MIC value of 5 ug mL-1 (15 of the 23 isolates). Infected fish exhibited acute clinical signs similar to a natural infection. The skin had severe ulcerative necrotizing dermatitis and the muscles had severe necrotizing myositis. The gills had severe multifocal necrotizing branchitis. The identity of the bacteria isolated from the challenged fish was confirmed by polymerase chain reaction and by genotyping. The results demonstrate that diquat would reduce mortalities caused by an acute columnaris infection.