First record of the fish pathogen Flavobacterium columnare genomovar II from bluegill, Lepomis macrochirus (Rafinesque), with observations on associated lesions

Abstract

Flavobacterium columnare is the causative agent of ‘columnaris disease’ (Davis 1922), a disease that kills or debilitates a wide ecological and phylogenetic spectrum of temperate and tropical freshwater fish (Bernardet 1989; Bernardet & Grimont 1989; Bernardet et al. 1996; Olivares-Fuster et al. 2007; Bullard, McElwain & Arias 2011). It is regarded as a predominant pathogen of fish maintained in both food production aquaculture systems and the ornamental fish trade (Decostere et al. 1999a,b; Schneck & Caslake 2006), and it is of special interest in warm-water aquaculture ponds in the southeastern US, where it is regarded as one of the primary bacterial pathogens that constrains culture of channel catfish, Ictalurus punctatus (Rafinesque) (see Thune, Stanley & Cooper 1993; Plumb 1999). Much of the biological information about this bacterium derives from aquaculture epizootics (Olivares-Fuster et al. 2007, 2011), wherein columnaris disease is marked by epidermal sloughing and scale loss concomitant with a symmetrical body discolouration that has been called ‘saddleback’ lesion (Cone, Miller & Austin 1980; Bullard et al. 2011). The 3 genomovars (Ursing et al. 1995) of F. columnare (see Triyanto & Wakabayashi 1999) exhibit differential virulence (Arias et al. 2004; ThomasJinu & Goodwin 2004; Darwish & Ismaiel 2005; Shoemaker et al. 2008), but information on their prevalence, host distribution and pathobiology is largely indeterminate. Bluegill, Lepomis macrochirus Rafinesque, is a widely introduced centrarchid that ranges throughout the Mississippi River and adjacent basins in North America. This fish was co-introduced as a forage fish for the recreationally prized largemouth bass, Micropterus salmoides (Lacepede), and its populations thrive along with those of largemouth bass in lakes, ponds and creek pools as well as densely vegetated shorelines of impoundments (Boschung & Mayden 2004). Bluegill is a generalist omnivore that tolerates a wide range of salinities and thermal regimes, which has contributed to its high level of invasiveness: now a documented invasive species in >20 countries (Kawamura et al. 2006; Fuller, Nico & Williams 1999). During 19–23 April 2012, a significant bluegill kill occurred throughout a series of hydrologically linked earthen ponds located in east-central Alabama (32°40′51.89′′N; 85°30′39.73′′W). Moribund bluegill were sampled for bacterial analysis with a sterile loop and cultured on Shieh agar supplemented with tobramycin at a concentration of 1 lg mL 1 (Decostere, Haesebrouck & Devriese 1997) at 28 °C for 48 h. Rhizoid, yellowpigmented colonies were considered putative F. columnare cultures and were re-isolated on Shieh agar lacking antibiotic. Pure cultures were incubated in Shieh broth at 28 °C with shaking Correspondence S A Bullard Department of Fisheries and Allied Aquacultures, 203 Swingle Hall, Auburn University, Auburn, Alabama 36849, USA (e-mail: ash.bullard@auburn. edu)