Treatment, Identification of: Aeromonas, Furunculosis, & Vibrio in Aquariums & Ponds

Also symptoms or manifestations of these bacterial pathogens such as Septicemia, Pop-Eye, Intestinal, swim bladder and occasionally Dropsy in Fresh or Saltwater.

Sections Include:
(1) Overview
(2) Vibrio
(3) Aeromonas
(4) Furunculosis
(5) Treatments
(6) Prevention
As a Cause of;
*Pop Eye
*Swim Bladder & Intestinal Infections
(7) Summary & Downloadable pdf Version of article

Aquarium, Pond Aeromonas, Septicemia symptoms 

By Carl Strohmeyer-PAMR 35+ years experience

Updated 12/19/15


Aeromonas and Vibrio are both anaerobic gram negative bacteria with similar manifestations such as infecting wounds, gastroenteritis, as well as being the primary bacterium cause of hemorrhagic septicemia. Other manifestations may include pop-eye and Dropsy.

  • Aeromonas is more common in freshwater while Vibrio is more common in brackish and saltwater.
  • Aeromonas salmonicida (commonly called Furunculosis ) is a variant of Aeromonas that is more common in coldwater, often affecting Koi and Trout.
  • Aeromonas is the most common cause of Septicemia (which is more a symptom or condition than an actual disease), that often shows as red streaks in fins as well as more severe symptoms (often there is little that can be done at this point other than prevent other fish from severe Aeromonas/Septicemia infections).
  • Aeromonas & the similar Pseudomonas Bacteria are a common cause of “Pop-Eye” in fish
  • Aeromonas is often a factor in intestinal infections or pathogen induced swim bladder problems
  • Dropsy can be caused by internal (systemic Aeromonas infections)

Please read further for more in depth descriptions and treatment/prevention methods for each.


Vibrio in brackish water scatVibrio is a lactose-fermenting, anaerobic, gram-negative bacteria. It is slightly curved and rod shaped, and is an opportunistic pathogen, found in saltwater/marine or brackish environments. This organism causes wound infections, gastroenteritis, and is a common cause of “hemorrhagic septicemia” (see the picture below in the Aeromonas section for Septicemia) where the microorganism enters the blood stream, resulting in septic shock, rapidly followed by death in many cases (about 50% of infections).
A common symptom in marine fish and brackish fish is red patches or red streaked fins, especially in Yellow Tangs and Marine Angels.
Kanamycin is very effective in the high pH applications where Vibrio is usually present.
Another older but useful antimicrobial for treatment of Vibrio is Triple Sulfa and it also is effective in high pH environments.
Pimafix and a tea made Usnea Lichen are natural treatments that have shown some effectiveness for Vibrio.
Treatment of wounds with Methylene Blue or Hydrogen Peroxide or a 30 minute double dose "Bath" with Methylene Blue OR Potassium Permanganate is also useful in treatment of Vibrio.


Aeromonas, goldfish

One of the most common infections in freshwater fish is caused by the rod-shaped bacteria Aeromonas, which is also a gram negative, facultatively anaerobic, lactose-fermenting bacterium.

This bacterial pathogen is common in goldfish and many Tropical Fish. This bacterial infection can show itself in a wide variety of symptoms. Affected fish may have shallow or deep ulcers somewhere on the body, but may exhibit other signs such as exophthalmia (pop-eye), areas of bloody spots, and a distended abdomen. Infected fish with open sores appear to spread the disease to other fish, and sub clinical carriers may exist, shedding bacteria in their feces.

Aeromonas, ulcersAeromonas infections are probably the most common bacterial disease to infect Tropical Freshwater Fish.
Mortality rates are often low (10% or less) and losses may occur over a period of time (2 to 3 weeks or longer). In these instances, some factor; often water quality induced stress has caused the fish to become more susceptible to the bacteria.

Common sources of poor water quality stress are;

  • overcrowding

  • Poor filtration or especially no filtration

  • High ammonia, nitrite, nitrate levels

  • Unstable pH

  • High amounts of organic decomposition (often in the gravel or filters).

Water quality, high amounts of organic decomposition, and low oxygen levels are major distinguishers between Aeromonas and the often confused with bacterial disease "Columnaris".
In my experience, with Aeromonas infections, decaying organics or many of the above noted water quality stressers are present often along with low oxygen levels and a Redox that is too low while Columnaris is often found in more well kept aquariums/ponds with stressers such as aggressive fish or too high Redox.

It should be also noted that since Aeromonas is facultatively anaerobic (aerobic respiration is advantageous, but not necessary), so improving oxygen levels and circulation is often important for prevention and recovery.
While Aeromonas can and does thrive in oxygen rich environments (in a test tube environment), in practical experience this anaerobic bacterium does not compete in aquariums or ponds with optimum parameters.

From my and other professionals thoughts as to why this is; In aquariums/ponds with decomposing organic waste, pure anaerobes make a suitable environment for the facultative anaerobic Aeromonas bacterium to flourish. So get rid of the anaerobes via the decomposing waste/mulm as well as improve other parameters that promote this anaerobic environment and you will get rid of the Aeromonas bacterium (obviously once fish are infected, treatments will also be necessary)

What is also noteworthy from my many years of experience with 1000s of clients over these years is that aquarium, bowls without any established bio filter have a VASTLY higher incidence of Aeromonas infections, whether internal or external or both.
Even a small tank such as a 2 gallon aquarium should really have an established bio filter, otherwise often even the best of treatment regimens may fail once an Aeromonas infections gets started.
Here is a source for a simple but effective aquarium/bowl bio filter:
AAP Hydro Sponge Filter Kits

Common Symptoms of Aeromonas are (expanded upon in further sections);
  • Intestinal Issues; such as loose feces (similar to diarrhea), or white (Mucous covered) feces often confused with internal nematode parasites, as well as intestinal swelling
  • Swim bladder infections (this can be caused by other pathogens)
  • Septicemia of the blood resulting in red streaks, sometimes incorrectly diagnosed as a disease unto itself (AKA Red Pest), when in fact it is a symptom.
  • Sores that continue to grow
  • Pop eye (this too can be caused by other pathogens)
  • Infections of the kidneys resulting in Dropsy (this too can have other pathogenic causes)
  • Sometimes Aeromonas can present as an aggressive case of fin rot that often spreads beyond the outer finnage (psuedomonas is the more common cause of Fin Rot).

Septicemia, blood streaks


Aeromonas (along with Vibrio in brackish and marine) are common causes of hemorrhagic septicemia (often incorrectly identified as a disease of its own and called "Red Pest"). The happens whereby where the microorganism enters the blood stream, resulting in septic shock, rapidly followed by death in many cases.
Clinical signs of Aeromonas septicemia range from mild symptoms of red streaks to more serious symptoms such as sudden death with high morbidity in peracute cases to superficial to deep skin lesions. Skin lesions include variously sized areas of hemorrhage and necrosis and the base of the fins.
These lesions may progress to reddish to gray ulcerations with necrosis of the underlying musculature.
Ulcers may be observed in conjunction with a hemorrhagic septicemia which can produce non-specific lesions and clinical signs of exophthalmos (Abnormal protrusion of the eyeball), ascites (An abnormal accumulation of serous fluid in the abdominal cavity), and visceral petechiation (Small red or purple spots on the body), and a hemorrhagic and swollen lower intestine and vent.
Anorexia and skin discoloration are also observed with the septicemia.

Pop Eye


As noted earlier, Aeromonas (along with Pseudomonas Bacteria which is also gram negative but is aerobic) is one of the more common causes of bacterial “pop-eye” in fish.
A recent university study dealing with Trout found that removing stressors and improving oxygen levels often cleared eye infections without medication (although sometimes direct medication applications such as Silver Nitrate or Potassium Permanganate and hospital tank treatment with Erythromycin or a Kanamycin/Nitrofurazone is necessary).

Even though Pop-Eye is a symptom of more than one possible cause (such as Aeromonas), one thing that is common to this malady is fluid build up behind the eye.
So improving osmotic function (as in Dropsy) with correct mineralization is important, as well medicated baths or dips are often useful in curing/treating this condition. I often find a dip to work better than a bath for a severe stubborn case of Pop-Eye where the causes have been eliminated, yet the fluid remains.

Please see these articles for more about Dips and Baths: Aquarium Disease Prevention; Section 9, Baths, Dips OR even more depth Fish Baths for treatment of bacterial infections, septicemia, more

See this article for more about Streptococcus as a cause of Eye Infections:
Streptococcus, Eye Infections


Aeromonas can also be a factor in swim bladder or intestinal problems, especially when food is allowed to decompose on the bottom of the aquarium where fish (especially goldfish) may come along and consume it; also soaking dry foods in water prior to feeding cuts down on intestinal Aeromonas infections (as does healthy water parameters).
Large amounts of decomposing organic debris on the bottom of the aquarium (especially with goldfish) can also be a cause intestinal Aeromonas infections, so good filtration and in between cleanings with tools such as the Eheim Sludge Remover Vacuum can help.
With Bettas, poor water conditions due to ammonia spikes and other water quality issues can be a cause of swim bladder Aeromonas infections. Since many bettas are not kept in filtered containers, I strongly recommend finding some way to either add a filter (such as Hydro Sponge #1) or adding products such as Matrix to the bowl bottom or better in a small flow through medicine bottle (AmmoChips and other similar products can be used, but these are not as effective long term for these ammonia spikes).

Generally for Swim Bladder infections simple baths described later in this article should be the first treatment step as well as withholding food for a couple days, and increasing mineral/electrolyte levels in the tank (this can be done with products such as Regular or Medicated Wonder Shells which are also especially helpful for fish such as Bettas not kept in filtered aquariums.

Another simple remedy for swim bladder issues is a thawed and shelled frozen pea fed to the fish. While this is more for constipation, if constipation is at the root or even just a part of the problem, this can help as can feeding frozen, live, or even FD Brine Shrimp.



When Aeromonas goes systemic (internal) it has been shown to be a major contributor to Dropsy (which is a kind of catch all diagnosis for bloating with distended scales usually caused by kidney and sometimes liver maladies).

Prevention is the key here;

  • Soak dry foods so as to not introduce air into the intestines which can start an Aeromonas infection in the intestines (gut) and swim bladder.
  • Good tank parameters including maintaining positive mineral ions
  • Use antibiotics sparingly, many have side affects on the liver and kidneys such as Neomycin and Tetracycline. Kanamycin (which is gram negative) is a better choice, although Neomycin when fed as a part of a medicated food can be useful.

Please see this more in depth article (from Aquarium Answers) about Dropsy: "Aquarium Answers; Dropsy in Fish"

Aeromonas, sores


Treatments of Aeromonas in tropical freshwater aquariums include:
Pimafix AND Melafix for mild infections, especially mild wound infections (Melafix by itself is rarely effective on Aeromonas though).
Nitrofurazone for more serious infections (this can be combined with Kanamycin for an even stronger combination treatment). Neomycin is an excellent antibiotic when mixed with food that delivers medications internally to infections (although this is primarily a gram positive antibiotic, it is anaerobic in activity and it should be combined with a gram negative antibiotic such as Kanamycin for better results).

Triple Sulfa is also a medication worth considering, especially in cases of Septicemia (caused by Aeromonas or other pathogens).
Although not the strongest medication for serious cases of Aeromonas, Triple Sulfa is often effective for the red streaks found in fins even though the fish may be healing otherwise. A Triple Sulfa treatment for red streaks is often boosted with the addition of a medicated bath using Methylene Blue and salt with direct application of Methylene Blue to the affected area immediately prior to the bath.
Please see this article for more about fish baths:
Fish Baths for treatment of bacterial infections, red streaks

Another antibiotic that may be worth considering for some Amazon River tanks is Minocycline (Link) which is found in Maracyn Two (do not confuse this with Maracyn One which contains Erythromycin which is rarely effective for Aeromonas) or Tetracycline Hydrochloride.
This said, both being Tetracyclines, these can have many drawbacks for many aquarium applications (including being less effective with gram negative bacterium) and should only used in rare instances (please follow the previously noted link for further information).

Aquarium Salt or Cichlid Salt can also be added at a rate of 1 tablespoon per 5 net gallons of water as an additional treatment to those above and the baths below (however sodium chloride rarely replaces these treatments, only compliments). Please see this article for more about the use of Aquarium Salt: “Aquarium Answers; Salt in Freshwater Aquariums”

For ulcerations I also recommend medicated baths of about 30 minutes using either Methylene Blue or Potassium Permanganate at double normal in tank strength using tank water for this bath, then disposing of the bath water after completion.
Potassium Permanganate is the slightly better choice for external infections of Aeromonas as it has more antibacterial properties due to oxidation.
Methylene Blue is the better choice for internal manifestations of this bacterial pathogen such as Swim Bladder, intestinal, Dropsy or Pop-Eye due to its effectiveness in tissue penetration.
In fact in Swim Bladder and intestinal Aeromonas infection, the MB Bath (along with possibly 1-2 teaspoons of salt and ¼ teaspoon of Epsom salt per gallon of bath water) followed by changes in water in the main aquarium, changing diet and/or withholding food for 2 days (dry foods should be soaked for 5 minutes prior to feeding), establishing a GH level of at least 100 ppm (for positive Calcium, Magnesium mineral ions) and 1 tablespoon of salt per 5 gallons may be all that is necessary for treatment.
If this does not remedy the problem then treatment with medications such as Kanamycin, Metronidazole, or Neomycin in a fish food soak. My preference for intestinal infections would be a combination of Metronidazole and Neomycin in this fish food soak (these can also be used in the bath, but are not as effective in reaching the source of the infection as fish food delivery).

Further Reading;
Aquarium Medications; Fish Food Medication Delivery

Product Resources:
AAP Neoplex
AAP Metronidazole


As noted earlier in the section dealing with Dropsy, water parameters, filtration and more is important for prevention AND ongoing treatment.

  • Good tank parameters including 0 ammonia/nitrites, low nitrates, and a stable pH/KH. Lower pH water can increase the virulence of Aeromonas, so low pH tanks tend to be more problematic to Aeromonas infections.

  • Low amounts of DOC (dissolved organic compounds), large amounts of organic mulm/decomposition which will often show up as an unstable pH and KH as well as occasionally high nitrates.

  • Aeromonas infections occur most often during environmental changes, stressors, changes in temperature, in contaminated environments, and when an organism is already infected with a virus or another bacterium.
    Aeromonas can also be ingested through food products contaminated with the Aeromonas bacterium. For this reason be careful to clean up uneaten food and to remove food that may get trapped in filters. As well, if the fish food method of aquarium cycling is used, it is best to dissolve it as a fine powder into water first before adding to the aquarium.

    Reference: Wikipedia; Aeromonas

  • Use of products such as Pillow Moss which are a natural way to maintain low pH soft water tank while not allowing Aeromonas infections.

  • Limit use of Activated Carbon.
    This is a double edged sword as activated carbon can help lower DOC, however it also can lower dissolved oxygen and provide an ideal surface area for anaerobic Aeromonas bacterial growth.
    Please see this in depth article for further information about this subject:
    Aquarium Answers; Activated Carbon

  • Good filtration that is regularly and properly cleaned (rinsed with de-chlorinated water, not straight tap water).

  • Good circulation which includes a dissolved oxygen 5-7 ppm since Aeromonas is an anaerobic bacteria (it thrives in LOW oxygen water). If you do not have this often difficult to find test kit, simply maintaining a combined aquarium water turnover of 5 times the aquarium size per hour. This counts all circulation devices such as air stones.

  • Proper mineralization is important for correct osmoregulation which in turn allows for better oxygen permeation (which recent studies show is important to fish eye infections). This is where the use of products such as Wonder Shells are helpful.

  • Too Low Redox; while I often discuss the fact that many aquarium keepers miss the importance of Redox Reducers so as to lower free radicals and for improved osmoregulation, a Redox that is too low or at least needs to be temporarily raised can help with Aeromonas and Vibrio bacterial infections. Generally this can be improved with simply increasing the circulation and oxygen content or for more drastic measures adding Potassium Permanganate can increase your aquarium or ponds Redox oxidation properties quite quickly.


Furunculosis, cold water fish, pond

In Coldwater freshwater fish the similar pathogen is Aeromonas salmonicida also known as furunculosis.
Treatment in Coldwater can be difficult as many treatments are not as effective below 65 degrees F.
Also Nitrofurazone, which is one of the treatments of choice in coldwater is less effective at the higher pH most coldwater fish prefer.

In higher pH applications (8.0 + in particular), Triple Sulfa and Kanamycin are generally the better choice. And on some strains of Furunculosis, Tetracycline has shown occasional effectiveness.
Another treatment in coldwater is Oxytetracycline, which works much better if soaked in the food and is especially useful when treating the water such as in a pond is undesirable.
A newer treatment preferred by many Koi keepers is KoiZyme (formally known as LymnoZyme). This is a formula of natural bacteria, enzymes, and micro nutrients that reduce the Aeromonas (and Pseudomonas) bacteria present in the water. It does not attack the bacteria directly, rather is out competes the Aeromonas bacteria for nutrients.

Pimafix often combined with Melafix is an organic treatment shown to be effective for Aeromonas, especially in pond applications.
Treatment of wounds with Mebromin or a 30 minute double dose dip with Methylene Blue is also useful in treatment of Aeromonas.

Product Resource: API Treatments; Pimafix & Melafix

Outside reference for Furunculosis:
Furunculosis and Other Diseases Caused by Aeromonas salmonicida (PDF)


It is important to note that both Aeromonas and Vibrio pathogens are opportunistic bacteria that are more virulent in poor water conditions.
It is important to affect a cure that water conditions are improved during treatment and not worsened by the treatment itself, which is why I do not recommend Tetracycline be used in display tank treatments of this disease as Tetracycline lowers red blood cell counts and binds calcium in the water which is essential for healing.
Regular partial water changes between treatments, stable pH and a proper functioning bio filter are all essential for effective cure and prevention.
I recommend good water parameters as prevention and to speed recovery during infections.

Here are a few parameters to consider:
*Ammonia/ Nitrites- 0 ppm
* Nitrates - under 40 ppm for freshwater/ 20 ppm for saltwater
*KH (Alkalinity)- 50 to 150 for freshwater (depending on the fish kept)/ 240 + for saltwater

For more about prevention I recommend this article: “Aquarium Disease Prevention”

Further references:


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