Fish with Pseudomoniasis

Koi with side ulcer possibly from pseudomoniasis

Pseudomonas is one of the bacteria species that might be found in your fish tank. Most aquarium bacteria, including those in your biological filtration system, are harmless, and some are even good to your fish. Other bacteria, on the other hand, wait until your fish's defenses are weakened before attacking, causing signs such as ragged fins, body sores, and loss of appetite.

A bacterium species seldom causes major issues in your fish on its own. They usually induce a secondary illness after a severe accident, transportation stress, or parasite infestation has debilitated the fish. Some Pseudomonas species, on the other hand, are capable of causing crippling sickness in otherwise healthy fish, and even death.

What Is Pseudomoniasis?

Pseudomoniasis is a bacterial infection caused by bacteria of the Pseudomonas genus. Pseudomonas infection is another name for it. There are many distinct Pseudomonas species in the aquatic environment, and the majority of them will not harm your fish. The majority of aquatic bacteria feed on debris that gathers on the aquarium's bottom, plant surfaces, and even the aquarium glass. They have no effect on the fish until the immune system has been weakened by another stressor event injury.

In pseudomoniasis, the fish's weakened immune system permits the bacteria to switch from benign into a harmful source of fish disease.

Symptoms of Pseudomoniasis in Fish

Fish Pseudomoniasis is similar to many other bacterial illnesses. These symptoms are prevalent with any bacterial fish sickness and are not particular to a Pseudomonas infection.


  • and redness at the base of the fins
  • or red spots on the skin
  • Lethargy
  • Decreased appetite
  • Sudden death

Red sores on your fish's body or ragged fins will most likely be your first clue that something is amiss. The sick fish will frequently hold its fins close to its body and may exhibit indications of lethargy, such as a lack of movement, drifting to lower levels of the tank, and a loss of appetite. You could see your fish quickly opening and shutting its mouth. However, the virus can sometimes kill the fish before symptoms appear.

Causes of Pseudomoniasis

Pseudomonas species may be found in practically all aquatic settings, although they usually only become pathogenic, or capable of causing sickness, when a fish becomes sick. Many infections, including Pseudomonas bacteria, may spread and thrive once a fish's defenses have been compromised. Certain Pseudomonas species, on the other hand, can cause illness even if the immune system hasn't been compromised.

Pseudomonas aeruginosa, which is found in the typical fish microbiome, is one such species. However, this bacterium species has evolved to be very opportunistic and harmful, allowing it to infect and sicken even otherwise healthy fish. Hemorrhagic septicemia, gill necrosis, abdominal distension, and internal organ failure are all symptoms of Pseudomonas aeruginosa.

If a fish's immune systems are continually weakened, or the bacteria are too plentiful, your fish will not recover without treatment.

Diagnosing Pseudomoniasis in Fish

Most fish owners don't take their sick fish to the veterinarian for diagnosis or treatment, though there are vets who specialize in aquatic pets.

When it comes to pseudomoniasis, the best diagnostic evidence comes from euthanizing a moribund fish (one that has significant clinical indications and is near to death) and sending the carcass to a veterinary lab for bacterial analysis. While euthanizing a fish is never pleasant, it may be done in a humane manner by submerging the ailing fish in a container filled with a 1:4 mix of vodka (or a comparable alcohol) and water. If you use 8 ounces of water, for example, you'll add 2 ounces of vodka. Within minutes, the fish will die of alcohol poisoning.

Tissues taken from the kidneys and spleen reveal a lot about which bacterium species is the underlying cause of sickness. If other fish in the tank are experiencing similar symptoms, it will be easier to treat them with medicines.

Additional diagnostics include bacterial culture of open wounds and antibiotic sensitivity testing. However, because exterior wounds provide a breeding ground for a variety of bacteria, the results may not be very specific as to the disease's true etiology.


The best strategy to cure Pseudomonas infections is to figure out what caused the fish's immune system to deteriorate in the first place. Poor water quality, insufficient or wrong diet, and aggressiveness or bullying difficulties are also common fish stresses. Better aquarium or pond upkeep, removing fish from the ecosystem, acquiring new food, and adding décor items or other environmental changes are all possible remedies, depending on the underlying issue.

Consult your aquatic veterinarian for tips on how to enhance your fish's environment and reduce stress. Treatments such as improving water quality or antibiotic medication will only give temporary comfort if the stressor is not addressed.

Your veterinarian can swab the sick fish's body for sores and send the samples to a lab to be cultured for Pseudomonas bacteria. An antibiotic sensitivity test can be done based on the bacteriology results to discover the most effective antibiotic for that specific bacterium. Because many Pseudomonas species are known to be resistant to various antibiotics, this is essential.

Your veterinarian will choose the best treatment technique after an appropriate antibiotic has been discovered. The medicine can be administered as a bath, in food, or directly injected into the fish, depending on the size, condition, and total number of fish affected.

Over the counter antibiotic-like products are usually not effective against Pseudomonas species bacteria.

Prognosis for Fish With Pseudomoniasis

Your fish is likely to live if it is just moderately unwell and receives quick treatment for the illness. Pseudomonas infection is more likely to kill fish that are seriously unwell or have not been treated with the proper medication.

How to Prevent Pseudomoniasis

The best way to keep Pseudomonas bacteria from spreading in your aquarium is to follow stringent quarantine procedures. This manner, if a stressed-out fish begins to show clinical indications as a result of capture, transit, and the new habitat, the sickness will not spread to the rest of your fish. Maintaining a clean, well-balanced aquarium water system, avoiding overloading the tank with too many fish, and giving a high-quality diet all contribute to keeping your fish healthy enough to battle illnesses before they start.

Is Pseudomoniasis Contagious to Humans?

Humans are not usually infected with Pseudomoniasis. Immunocompromised people, children, and the elderly should avoid coming into touch with aquarium water merely to be safe. Fish Mycobacterium is the most prevalent fish bacteria with the potential to infect humans, and it may cause serious skin sores in humans.