Species Profile - Aeromonas salmonicida

Aeromonas salmonicida Emmerich and Weible, 1890

Common Name: Furunculosis, ulcer disease, erythrodermatitis

Synonyms and Other Names:

Bacillus salmonicida, Bacterium salmonicida, and Bacterium trutta, AS

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).


This map only depicts Great Lakes introductions. Click here for Great Lakes region collection information

Great Lakes Nonindigenous Occurrences: A. salmonicida was first introduced to the Great Lakes drainage prior to 1902, but the site of the original introduction within the basin is unknown (Mills et al. 1993). It has been documented in all five Great Lakes.

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Aeromonas salmonicida are found here.

State/Province	First Observed	Last Observed	Total HUCs with observations†	HUCs with observations†
	1902	1902	*
MI	2005	2005	3	Betsie-Platte; Lone Lake-Ocqueoc; Manistee
NY	1999	2015	2	Lake Ontario; Salmon
WI	2004	2015	2	Door-Kewaunee; Pike-Root

Table last updated 4/18/2024

† Populations may not be currently present.

* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

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. A. salmonicida has been documented in Chinook Salmon (Oncorhynchus tshwyatscha), Coho Salmon (Oncorhynchus kisutch), Brown Trout (Salmo trutta) and Lake Trout (Salvelinus namaycush) in the Great Lakes.

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 (Salvelinus fontinalis) or Char (Salvelinus alpinus). 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.

Great Lakes Impacts:

Summary of species impacts derived from literature review. Click on an icon to find out more...

Environmental Socioeconomic Beneficial

There is little or no evidence to support that Aeromonas salmonicida has significant environmental impacts in the Great Lakes.

Realized:
In the Great Lakes and connecting tributaries, A. salmonicida has had a larger impact on native salmonids than on introduced salmonids. It primarily affects Atlantic Salmon (Salmo salar), Brook Trout (Salvelinus fontinalis), Lake Trout (Salvelinus namaycush), and Lake Whitefish (Coregonus clupeaformis). It secondarily affects other native non-salmonid 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) (Crawford 2001, Mills et al. 1993). Aeromonas salmonicida has been found to be ubiquitous and established in commercial fish farms, government fish hatcheries, and wild populations throughout the Great Lakes and connecting tributaries (Bruneau et al. 1999). However, the bacterium continues to be detected at very low prevalence (GLFHC 2006).

In 2011, A. salmonicida was isolated from a Michigan state hatchery for the first time since 2005 and was detected in 2% of returning adult Atlantic salmon collected from the St. Mary’s River (GLFHC 2012). Following elevated mortalities observed in Michigan in 2011, twenty cases of production and brood stock Atlantic Salmon were tested for pathogens. Aeromonas salmonicida was detected in three of the twenty cases. However, analysis showed that furunculosis was not the cause of mortality (GLFHC 2012). Elsewhere in the Great Lakes region, seven of fourteen Pennsylvania state hatcheries tested positive for A. salmonicida in 2011 (GLFHC 2012).

Aeromonas salmonicida is known to infect Arctic Grayling (Thymallus arcticus), a species once prevalent in the Great Lakes until the 1930s (Hubbs and Lagler 1958). Between 1987 and 1991, the Michigan DNR unsuccessfully attempted to reintroduce grayling to Lake Michigan. Since 2010, owners of the 40-acre Brookhaven Lake (MI) have been attempting to reestablish this species. The first grayling were introduced to the lake in fall 2011, with plans to introduce 500 more in 2012 (Sanderson 2012). If furunculosis becomes established in this system, negative impacts on the grayling population could be realized.

In many fish farms, antibacterial agent resistance among different species and strains of bacteria has become a major problem (Schmidt et al. 2000). Aeromonas 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 among salmonid populations (Bakke and Harris 1998).

In salmonid hosts that contract furunculosis as a result of infection by A. salmonicida, symptoms can include furuncles, hemorrhaging, enlarged organs, erratic swimming, and lack of feeding (Cipriano and Bullock 2001, Crawford 2001). Because of this, infected fish may be more susceptible to predation (Lafferty and Morris 1996). However, cascading food web effects as a result of furunculosis infection in the Great Lakes have not been reported.

There is little or no evidence to support that Aeromonas salmonicida has significant socio-economic impacts in the Great Lakes.
Realized:
Non-native Great Lakes wild and cultured salmonid populations susceptible to A. salmonicida infection include Coho Salmon (Oncorhynchus kisutch), Brown Trout (Salmo trutta), Chinook Salmon (O. tshawytscha), and Rainbow Trout (O. mykiss) (GLFHC 2006, GLFHC 2012). Prevalence of A. salmonicida in these species is low to moderate and mortalities are rare. For instance, in fall 2011, A. salmonicida was detected at 20% prevalence in returning feral Chinook brood stock spawners in a Michigan weir and at 4% prevalence in Coho Salmon from another (GLFHC 2012). That same year, A. salmonicida was isolated from 19 of 120 Coho salmon and 20 of 60 Seeforellen Brown Trout in Wisconsin hatcheries (GLFHC 2012). Furthermore, asymptomatic A. salmonicida infections were detected in four Indiana state hatcheries in 5 of 60 yearling Rainbow Trout, 1 of 30 young-of-year Chinook salmon, and 4 of 30 young-of-year summer-run steelhead (GLFHC 2012). An outbreak of furunculosis occurred in Brown Trout from the Curtis Creek Trout Rearing Station (Indiana) in June 2011, but the fish recovered following administration of medicated feed (GLFHC 2012). Prevalence of A. salmonicida in Coho and Chinook Salmon from New York state hatcheries continued to be low, and asymptomatic A. salmonicida infections were observed in 8 of 62 adult Chinook and 5 of 12 Coho Salmon in Ontario, Canada (GLFHC 2012).

Infectious diseases cost Canadian aquaculture industry over $400 million annually, with furunculosis accounting for approximately 10% in annual losses (Nash et al. 2006). The proportion of these losses specific to the Great Lakes region has not been reported. Likewise, the economic impact of pathogen screening requirements for the baitfish and aquaculture industries (see Management) are likely to be significant, but have not been documented.

Potential:
Aeromonas spp. are significant human pathogens, causing extra-intestinal infections in various organs (von Graevenitz and Mensch 1968). However, A. salmonicida is a fish pathogen and has not been associated with human infection (Janda and Abbott 1996). Atypical A. salmonicida is introduced and common among Goldfish in Australia (Humphrey and Ashburner 1993, Trust et al. 1980). 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 (Bakke and Harris 1998, Morrison 1995).

There is little or no evidence to support that Aeromonas salmonicida has significant beneficial effects in the Great Lakes.
Potential:
In lab environments, the A. salmonicida 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 (Gu and Mitchell 2002, Maki et al. 1998).

Management:

Regulations (pertaining to the Great Lakes)

The Great Lakes Fishery Commission lists Aeromonas salmonicida as a restricted pathogen - hatchery stocks are routinely tested for the pathogen and fish exhibiting clinical symptoms are not to be transferred, stocked or released.

Ohio requires source facilities outside the Great Lakes basin to document annual health inspections showing no furunculosis occurrences for the previous five years prior to importing salmonids to the Lake Erie watershed (Baird 2005). Indiana requires source facilities outside the basin to document they are furunculosis free prior to importing salmonid stock. Salmonids found carrying the pathogen, but asymptomatic, can be sold in state if source facilities are within the Great Lakes basin (Baird 2005). Michigan, Illinois, Wisconsin, and Minnesota also require imported salmonid health inspections. However, A. salmonicida is not a targeted pathogen. Minnesota allows the importation of furunculosis infected eggs, if prior egg treatments are approved (Baird 2005).

New York, Pennsylvania, Michigan, Illinois, Wisconsin, and Minnesota have instated similar baitfish regulations to control the spread of furunculosis and other fish pathogens. Those of New York include that bait harvested from inland waters for personal use is only permitted to be used within the same body of water from which it was taken and cannot be transported overland (with the exception of smelt, suckers, alewives, and blueback herring). Once transported, baitfish cannot be replaced to its original body of water (NYSDEC 2012).

Live or frozen bait harvested from inland New York waters for commercial purposes is only permitted to be sold or possessed on the same body of water from which it was taken and cannot be transported over land unless under a permit and or accompanied by a fish health certification report. Bait that is preserved and packaged by any method other than freezing, such as salting, can be sold and used wherever the use of bait fish is legal as long as the package is labeled with the name of the packager-processor, the name of the fish species, the quantity of fish packaged, and the means of preservation (NYSDEC 2012).

Certified bait may be sold for retail and transported overland as long as the consumer maintains a copy of a sales receipt that contains the name of the selling vendor, date sold, species of fish sold, and quantity of fish sold. Bait that has not been certified may still be sold but the consumer must maintain a sales receipt containing the body of water where the bait fish was collected and a warning that the bait cannot be transported by motor vehicle. Bait sold for resale require a fish health certification along with a receipt that contains the name of the selling vendor, date sold, species of fish sold, and quantity of fish sold, which must be kept for 30 days or until all bait is sold (NYSDEC 2012).

In addition to baitfish protections, prior to placing fish in New York waters, a fish health certification report must document that the fish are furunculosis free.

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Control
Biological
While supplements of lactic acid bacteria (Carnobacterium spp.) given with fish feed do not protect against A. salmonicida infection (Gildberg et al. 1995), such probiotic supplementation (also A. hydrophila and Vibrio fluvialis) can decrease mortality in Atlantic salmon (Salmo salar) and Rainbow trout (Oncorhynchus mykiss) infected with A. salmonicida (Irianto and Austin 2002). Carnobacterium strain K1 colonizes the intestinal tract of Rainbow trout and inhibits A. salmonicida growth (Jöborn et al. 1997). Short-term bathing of presmolt Atlantic salmon infected with furunculosis with siderophore-producing Pseudomonas fluorescens is another successful biological control (Gram et al. 1999, Smith and Davey 1993). Bath treatments with V. alginolyticus (Austin et al. 1995) can also lead to a reduction in mortality (Verschuere et al. 2000).

Administration of bacteriophage to infected fish may also help control outbreaks. In a study that administered the bacteriophage HER 110 to A. salmonicida HER 1107 infected Brook trout (Salvelinus fontinalis), A. salmonicida populations declined by six log units (base 10) in 3 d. Further tests within fish populations are necessary to better understand the implementations of this alternative therapy (Imbeault et al. 2006).
The U.S. FDA approved vaccine cefuroxime administered to brood stock prior to spawning has proven to be very effective at reducing A. salmonicida prevalence (GLFHC 2006). Very good to excellent results controlling and preventing out-breaks of furunculosis have also been obtained using an autogenous vaccine, produced by Microtechnologies; this treatment was accompanied by an immune-enhancing feed administered for three weeks prior and three weeks post vaccination, as well as stock thinning to reduce overall stress (GLFHC 2006).

Physical
There are no known physical control methods for this species.

Chemical
Antimicrobial agents used to treat A. salmonicida infections include thiophenicol, furazolidone (Herman 1968), oxytetracycline (Heo and Seo 1996, Herman 1968, Wiklund and Dalsgaard 1998), sulphamerazine, tetracycline and a combination of trimethoprim (Heo and Seo 1996, Wiklund and Dalsgaard 1998) and sulphonamide (McCarthy and Roberts 1980). Others include flumequine (Michel et al. 1980), oxolinic acid (Hastings and McKay 1987, Heo and Seo 1996, Wiklund and Dalsgaard 1998), florfenicol (Inglis et al. 1991b), amoxycillin (Inglis et al. 1992), enrofloxacin (Stoffregen et al. 1993), chloramphenicol, neomycin, nitrofurantoin and ciprofloxacin (Heo and Seo 1996, Wiklund and Dalsgaard 1998). Feed containing terramycin and romet are effective in treating A. salmonicida (MDNR 2012).

However, an increase in antimicrobial resistance was recognized in the United States beginning in 1967 (Wood 1967). Antimicrobial resistance by A. salmonicida has been discovered with the following agents: sulphonamides (Herman 1968), oxytetracycline (Grant and Laidler 1993, Inglis et al. 1991a, Tsoumas et al. 1989), a combination of sulphonamide and trimethoprim (Grant and Laidler 1993, Tsoumas et al. 1989), oxolinic acid (Grant and Laidler 1993, Hastings and McKay 1987, Höie 1992, Inglis et al. 1991a, Oppegaard and Sörum 1994, Tsoumas et al. 1989), flumequin (Höie 1992), and amoxycillin (Grant and Laidler 1993).The U.S. FDA approved broad-spectrum, in-feed antibiotic florfenicol is now available to control mortality in finfish due to furunculosis (MAA 2012).

Other
Minimizing fish stress can reduce the risk of disease outbreak (FTS 2012).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Remarks: A. salmonicida has also previously been known as Bacillus salmonicida, Bacterium salmonicida, and Bacterium trutta.

References (click for full reference list)

Other Resources:

Author: Kipp, R.M., A.K.Bogdanoff, A. Fusaro and R. Sturtevant

Contributing Agencies:

Revision Date: 8/21/2018

Citation for this information:
Kipp, R.M., A.K.Bogdanoff, A. Fusaro and R. Sturtevant, 2024, Aeromonas salmonicida Emmerich and Weible, 1890: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/GreatLakes/FactSheet.aspx?Species_ID=2353, Revision Date: 8/21/2018, Access Date: 4/18/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.