Heterogeneity of Aeromonas populations in wild and farmed perch, Perca fluviatilis L.

Abstract

The aeromonads comprise a diverse group of waterborne bacteria found within the gamma-proteobacteria. The last two decades have seen marked advances in Aeromonas taxonomy, and over 20 validated species are now recognized (for a recent review see Janda & Abbott 2010). Aeromonas species are well-known agents of fish disease, and this is reflected in the number of Aeromonas species originally described in diseased fish including Aeromonas allosaccharophila (Martinez-Murcia et al. 1992), Aeromonas aquariorum (Martinez-Murcia et al. 2008), Aeromonas bestiarum (Ali et al. 1996), Aeromonas piscicola (Beaz-Hidalgo et al. 2009), Aeromonas sobria (Popoff & Veron 1976) and four subspecies of Aeromonas salmonicida: A. salmonicida subsp. salmonicida (Griffin, Snieszko & Friddle 1953), A. salmonicida subsp. achromogenes (Smith 1963), A. salmonicida subsp. masoucida (Kimura 1969a,b) and A. salmonicida subsp. smithia (Austin, McIntosh & Austin 1989). Probably the best characterized of these is A. salmonicida subsp. salmonicida, the aetiological agent of furunculosis, which affects salmonid fish. In cases of acute disease, onset of mortality is rapid and mortality rates are high. Other species including Aeromonas hydrophila and A. veronii biovar sobria have been associated with ulcerative disease in farmed fish such as carp, catfish, koi and trout (Rahman et al. 2002; Kozinska 2007; Orozova et al. 2009; BeazHidalgo et al. 2010). Most recently, A. sobria has been identified as a causative agent of tail rot in tilapia (Li & Cai 2011), and A. veronii has been associated with infectious dropsy in oscar (Sreedharan, Philip & Singh 2011). In Switzerland, A. sobria was isolated from the skin lesions and internal organs of perch, Perca fluviatilis L., farmed in a freshwater lake. Diseased animals presented focal ulcers and fin rot (Wahli et al. 2005). Isolates taken from these diseased, farmed perch were able to induce similar clinical signs under experimental conditions indicating A. sobria was the causative agent of the disease (Wahli et al. 2005). A subsequent study, however, found A. sobria and A. veronii were among the dominant members of the intestinal microbiota of wild perch caught in the same lake and presenting no signs of disease (Goldschmidt-Clermont et al. 2008). The study described here aimed to determine whether these wild perch served as a reservoir of infection of farmed animals, or whether the A. sobria strains causing disease in farmed perch were distinct from those found to colonize the wild perch population. Fifty-two Aeromonas strains were isolated, from 2001 to 2005, from two distinct perch populations; a population of farmed fish reared in open pens on a freshwater lake and a population of wild perch caught in the same lake. Strains were initially isolated from material taken from perch organs (skin, intestine, kidney, spleen and liver; Table 1) with sterile loops and inoculated onto Columbia Journal of Fish Diseases 2012, 35, 607–613 doi:10.1111/j.1365-2761.2012.01388.x