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| NAS - Nonindigenous Aquatic Species |
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Common Name: furunculosis, ulcer disease, erythrodermatitis
Synonyms and Other Names: Bacillus salmonicida, Bacterium salmonicida, and Bacterium trutta
Taxonomy: available through 
Identification: A. salmonicida is a gram-negative, non-spore-forming and generally non-motile bacterium that can grow as single or paired rods of varying lengths or occasionally as coccoid cells. The rod-shaped form usually occurs in blood, lesions, and liquid media while the coccus form grows on agar media. Bacterial colonies on agar plates are round, translucent yellow and slightly convex. When grown in any medium, a brown soluble pigment is produced after a number of days. A motile form of this bacterium has also been identified (Marsh 1902; Mills et al. 1993; Kozinska et al. 2002).
In salmonid hosts that contract furunculosis as a result of infection by A. salmonicida, symptoms can include: furuncles (boil-like lesions) that develop in internal tissues and work their way out; overall darker color; hemorrhaging in the fin bases, mouth, abdominal walls, reproductive organs, viscera, liver, pyloric caeca, and heart; enlarged spleen; soft kidneys; erratic swimming; lack of feeding; and congested intestines. Severe septicemia and acute mortality sometimes occur (Cipriano and Bullock 2001; Crawford 2001).
An atypical form of A. salmonicida is likely responsible for ulcer disease in some species of trout. This disease does not infect the blood, liver, kidneys, or spleen, but can cause intestinal congestion. Throughout the course of the disease, the epidermis thickens and turns white, then grey, and finally dark red, as ulcers develop. Ulcers start externally and move inwards. They develop on the body, fins, jaw, or in the mouth (Cipriano and Bullock 2001).
In goldfish, ulcer disease may also develop, and manifests itself as white ulcers on the epithelium, which turn into hemorrhages below the scales. Lesions can cause some muscle degeneration (Cipriano and Bullock 2001).
Another atypical form of A. salmonicida may be responsible for carp erythrodermatitis, which results in skin hemorrhages. The bacterium resides between the dermis and epidermis of the infected host. Hemorrhages may reach the gills and eventually result in abdominal distention and anemia (Cipriano and Bullock 2001).
Size: rods vary in length from 0.5-6 µm and in width from 0.5-1 µm, whereas cocci vary in diameter from 0.5-1 µm (Marsh 1902)
Native Range:
Unknown. A. salmonicida was first discovered to be the pathogen responsible for salmonid furunculosis in Germany (Mills et al. 1993).
Nonindigenous Occurrences: A. salmonicida was first introduced to the Great Lakes drainage prior to 1902 but the site of the original introduction occurred within the basin is unknown (Mills et al. 1993).
Ecology: A. salmonicida can cause disease in fishes across a broad range of temperatures in marine and freshwater environments. It typically occurs in aquaculture and hatchery environments, but can also become established in the wild amongst introduced and native fish populations.
There are various strains of the bacterium with differing and complex taxonomies, probably including a few subspecies. Forms vary genetically and biochemically, and both typical and atypical types of the bacteria can be either motile or non-motile. Typical forms usually cause furunculosis in cold water salmonid species, and are particularly pathogenic to brook trout or char (Salvelinus fontinalis). Atypical forms generally cause dermal ulcers and external pathological symptoms in other fish species, and may or may not lead to septicemia in the host. Interestingly, atypical forms of the species isolated from non-salmonids can sometimes cause typical symptoms in salmonids.
Nonpathogenic infections have been observed in a diverse array of fishes, but a few pathogenic infections in species other than salmonids have also occurred in such hosts as marbled sole (Pleuronectes yokohamae), Japanese flounder (Parlichthys olivaceus), and spotted halibut (Verasper variegatus) (Marsh 1902; Carson and Handlinger 1988; Mills et al. 1993; Cipriano et al. 1996; Bakke and Harris 1998; Cipriano and Bullock 2001; Crawford 2001; Martinez-Murcia et al. 2005; Kumagai et al. 2006).
There are acute, chronic and carrier forms of A. salmonicida, and the impact of the disease increases with increasing environmental degradation and pollution. Many strains can grow at 20–37°C, although growth has also been recorded below 18°C, but not below 6°C, for some strains. Infection can occur at 11 °C or less for typical forms but there often will be no symptoms in host fish at such low temperatures. Optimum pH is around 6.4–8.0 but overall tolerance ranges from 5.3–9.0. This disease can be passed on via cohabitation, fish to fish contact, use of aerosols in aquaculture environments, ingestion of infected prey items, and cohabitation with infected mollusks (Marsh 1902; Post 1983; Arkoosh et al. 1998, 2004; Cipriano and Bullock 2001; Kozinska et al. 2002; Martinez-Murcia et al. 2005).
Means of Introduction: A. salmonicida was very likely introduced with stocked nonindigenous fish species, such as brown trout (Salmo trutta) (Mills et al. 1993; Crawford 2001).
Status: Very likely established throughout all of the Great Lakes drainage system.
Impact of Introduction:
A) Realised: In the Great Lakes and connected tributaries, A. salmonicida has had a much larger impact on native salmonids than on introduced salmonids. It particularly affects Atlantic salmon (Salmo salar), brook char or trout (Salvelinus fontinalis), lake char (Salvelinus namaycush), grayling (Thymallus arcticus), and lake whitefish (Coregonus clupeaformis). It secondarily affects other non-salmonid native fish species such as northern pike (Esox lucius), yellow perch (Perca flavescens), dace and minnows (family Cyprinidae), catfish (family Ictaluridae), sticklebacks (family Gasterosteidae), and sculpins (family Cottidae). Among the introduced fishes affected in the Great Lakes basin are brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss) and other Pacific salmonids (Oncorhynchus spp.), goldfish (Carassius auratus) and common carp (Cyprinus carpio) (Mills et al. 1993; Crawford 2001).
Throughout watersheds in Ontario, A. salmonicida was ubiquitous and established in commercial fish farms, government fish hatcheries and wild populations from 1981–1994, although generally at very low rates in all environments (Bruneau et al. 1999). The bacterium continues to be detected, particularly in salmonid populations, throughout the Great Lakes drainage in cultured and wild environments, although generally at low prevalence rates (Great Lakes Fish Health Committee 2006).
B) Potential: In many fish farms, antibacterial agent resistance amongst different species and strains of bacteria has become a major problem (Schmidt et al. 2000). A. salmonicida is capable of transferring plasmids that confer drug resistance from one strain to another, which has the potential to result in new and more virulent strains of the disease evolving and appearing amidst salmonid populations (Bakke and Harris 1998). In lab environments this bacterium can be pathogenic to zebra mussels (Dreissena polymorpha). In the wild, mussel populations may act mainly as reservoirs for A. salmonicida, and further research is necessary to understand the ecology of the interaction between these species (Maki et al. 1998; Gu and Mitchell 2002). Atypical A. salmonicida is introduced and common amongst goldfish in Australia (Trust et al. 1980; Humphrey and Ashburner 1993). There have been major epidemics of this bacterium in salmonid populations, particularly in fish farms and hatcheries in the United Kingdom, Norway, and on the west coast of North America in British Columbia and Washington State (Morrison 1995; Bakke and Harris 1998).
Remarks: A. salmonicida has also previously been known as Bacillus salmonicida, Bacterium salmonicida, and Bacterium trutta.
References
Arkoosh, M. R., E. Casillas, E. Clemons, A. N. Kagley, R. Olson, P. Reno, and J. Stein. 1998. Effect of pollution of fish diseases: potential impacts on salmonid populations. Journal of Aquatic Animal Health 10(2):182-190.
Arkoosh, M. R., E. Clemons, A. N. Kagley, C. Stafford, A. C. Glass, K. Jacobson, P. Reno, M. S. Myers, E. Casillas, E. Loge, L. L. Johnson and T. K. Collier. 2004. Survey of pathogens in juvenile salmon Oncorhynchus spp. migrating through Pacific northwest estuaries. Journal of Aquatic Animal Health 16(4):186-196.
Bakke, T. A. and P. D. Harris. 1998. Diseases and parasites in wild Atlantic salmon (Salmo salar) populations. Canadian Journal of Fisheries and Aquatic Sciences 55(Suppl. 1):247-266.
Bruneau, N. N., M. A. Thorburn, and R. M. W. Stevenson. 1999. Occurrence of Aeromonas salmonicida, Renibacterium salmoninarum, and Infectious Pancreatic Necrosis Virus in Ontario salmonid populations. Journal of Aquatic Animal Health 11:350-357.
Carson, J. and J. Handlinger. 1988. Virulence of the aetiological agent of goldfish ulcer disease in Atlantic salmon, Salmo salar L. Journal of Fish Diseases 11:471-479.
Cipriano, R. C. and G. L. Bullock. 2001. Furunculosis and other diseases caused by Aeromonas salmonicida. Fish Disease Leaflet 66. United States Geological Survey. 33 pp.
Cipriano, R. C., L. A. Ford, J. D. Teska, J. H. Schachte, C. Petrie, B. M. Novak, and D. E. Flint. 1996. Use of non-lethal procedures to detect and monitor Aeromonas salmonicida in potentially endangered or threatened populations of migrating and post-spawning salmon. Diseases of Aquatic Organisms 27:233-236.
Crawford, S. S. 2001. Salmonine Introductions to the Laurentian Great Lakes: An Historical Review and Evaluation of Ecological Effects. Canadian Publication of Fisheries and Aquatic Sciences 132. 205 pp.
Dalsgaard, I., B. K. Gudmundsdottir, S. Helgason, S. Hoie, O. F. Thoresen, U.-P. Wichardt, and T. Wiklund. 1998. Identification of atypical Aeromonas salmonicida: inter-laboratory evaluation and harmonization of methods. Journal of Applied Microbiology 84:999-1006.
Great Lakes Fish Health Committee. 2006. Annual Agency Reports. 58 pp.
Gu, J.-D and R. Mitchell. 2002. Indigenous microflora and opportunistic pathogens of the freshwater zebra mussel, Dreissena polymorpha. Hydrobiologia 474:81-90.
Humphrey, J. D. and L. D. Ashburner. 1993. Spread of the bacterial fish pathogen Aeromonas salmonicida after importation of infected goldfish, Carassius auratus, into Australia. Australian Veterinary Journal 70:453-454.
Kozinska, A., M. J. Figueras, M. R. Chacon and L. Soler. 2002. Phenotypic characteristics and pathogenicity of Aeromonas genomospecies isolated from common carp (Cyprinus carpio L.). Journal of Applied Microbiology 93(6):1034-1041.
Kumagai, A., K. Sugimoto, D. Itou, T. Kamaishi, S. Miwa and T. Iida. 2006. Atypical Aeromonas salmonicida infection in cultured marbled sole Pleuronectes yokohamae. Fish Pathology 41(1):7-12.
Maki, J. S., G. Patel, and R. Mitchell. 1998. Experimental pathogenicity of Aeromonas spp. for the zebra mussel, Dreissena polymorpha. Current Microbiology 36(1):19-23.
Marsh, M. C. 1902. Bacterium truttae, a new species of bacterium pathogenic to trout. Science 16(409):706-707.
Martinez-Murcia, A. J., L. Soler, M. Jose Saavedra, M. R. Chacon, J. Guarro, E. Stackebrandt, and M. Jose Figueras. 2005. Phenotypic, genotypic, and phylogenetic discrepancies to differentiate Aeromonas salmonicida from Aeromonas bestiarium. International Microbiology 8:259-269.
Mills, E. L., J. H. Leach, J. T. Carlton and C. L . Secor. 1993. Exotic Species in the Great Lakes: A History of Biotic Crises and Anthropogenic Introductions. Journal of Great Lakes Research 19(1):1-54.
Morrison, D. 1995. Furunculosis in the British Columbia and Washington State salmon farming industries. Managing furunculosis in the 90s. Proceedings of the 2nd BCMAFF workshop on furunculosis. Bulletin of the Aquaculture Association of Canada 95:3.
Post, G. 1983. Textbook of Fish Health. T. F. H. Publications, Inc. Ltd., The British Crown Company of Hong Kong. 256 pp.
Schmidt, A. S., M. S. Bruun, I. Dalsgaard, K. Pedersen, and J. L. Larsen. 2000. Occurrence of antimicrobial resistance in fish-pathogenic and environmental bacteria associated with four Danish rainbow trout farms. Applied and Environmental Microbiology 66(11):4908-4915.
Trust, T. J., A. G. Khouri, R. A. Austen, and L. D. Ashburner. 1980. First isolation in Australia of atypical Aeromonas salmonicida. FEMS Microbiology Letters 9:39-42.
Author: Rebekah M. Kipp
Contributing Agencies: 
NOAA - GLERL
Revision Date: 4/26/2007 Citation for this information:
Rebekah M. Kipp. 2009. Aeromonas salmonicida. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=2353> Revision Date: 4/26/2007
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