Lack of association between Flavobacterium columnare genomovar and virulence in hybrid tilapia Oreochromis niloticus (L.) x Oreochromis aureus (Steindachner)

Authors: Shoemaker, Craig; Lafrentz, Benjamin

Submitted to: Journal of Fish Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2014
Publication Date: 8/1/2014
Publication URL: http://handle.nal.usda.gov/10113/62184
Citation: Shoemaker, C.A., Lafrentz, B.R. 2014. Lack of association between Flavobacterium columnare genomovar and virulence in hybrid tilapia Oreochromis niloticus (L.) x Oreochromis aureus (Steindachner). Journal of Fish Diseases. 38:491-498.

Interpretive Summary: Columnaris disease is a bacterial disease of fish that can be problematic in tilapia (Oreochromis spp.) aquaculture production. An understanding of the mechanisms in which Flavobacterium columnare causes disease is needed for the development of prevention strategies. The objective of this study was to determine if genetically different isolates of F. columnare differ in their ability to cause disease in sex reversed hybrid tilapia. A series of immersion disease trials were performed using isolates of the five established genetic types of F. columnare: I, II, II-B, III, and I/II. Contrary to previous work in catfish and rainbow trout, there did not appear to be an association between genetic type of F. columnare and ability to cause disease in tilapia. The disease model used resulted in acute mortality. An alternative disease model was tested by cohabitating healthy fish with fish that died due to columnaris disease. This method resulted in rapid appearance of clinical signs (skin depigmentation and loss of mucus within 1-2 h) and mortality, suggesting the potential for an enhanced ability of F. columnare to cause disease upon growth on/in a fish host. This study highlights the importance of removing mortalities and moribund fish with columnaris disease from aquaculture systems to reduce the infectious pressure of F. columnare on the fish population.

Technical Abstract: Columnaris disease can be problematic in tilapia (Oreochromis spp.) production. An understanding of the pathogenesis and virulence of F. columnare is needed for the development of prevention strategies. The objective of this study was to determine the virulence of genetically defined isolates of Flavobacterium columnare in sex reversed hybrid tilapia, O. niloticus (L.) × O. aureus (Steindachner). A series of immersion challenge trials were performed using isolates of the five established genomovars of F. columnare: I, II, II-B, III, and I/II. The mean percent mortality of fish challenged with genomovar I, II, and III isolates ranged from 0-100, 3.3-78, and 3.3-75%, respectively. The mean percent mortality of fish challenged with genomovar II-B ranged from 35-96.7%, and the only genomovar I/II isolate tested caused no mortality. Contrary to previous work in other fish species, there did not appear to be an association between F. columnare genomovar and virulence in tilapia. The challenge model used resulted in acute mortality and an alternative challenge model was tested by cohabitating healthy fish with dead fish infected with F. columnare. This method resulted in rapid appearance of clinical signs and mortality, suggesting the potential for F. columnare to increase in virulence upon growth on/in a fish host.