Aquarium granuloma: symptoms and treatment pool granuloma

An aquarium granuloma, also called swimming pool granuloma, is a skin disorder caused by the bacterium Mycobacterium marinum. This culprit especially thrives in fresh water at a temperature of 25-30°C, such as freshwater aquariums. The bacteria can easily penetrate minimally damaged skin (via an abrasion, crack or other minor damage to the skin) and cause an infection. Symptoms of an aquarium granuloma include a red, thickened skin reaction and usually the lymph nodes in the armpit are also slightly enlarged. Without therapy, the skin defect often heals within one to two years with scarring. Treatment is with antibiotics for two to three months. By properly protecting yourself by wearing gloves when cleaning the aquarium, aquarium granuloma can be prevented. The prognosis is generally excellent with appropriate treatment. Scars may remain after healing.

  • What is an aquarium granuloma?
  • Synonyms
  • Causes of aquarium granuloma
  • Risk factors for pool granuloma
  • Incubation period
  • Who gets it?
  • Symptoms of aquarium granuloma
  • Examination and diagnosis
  • Physical examination and skin biopsy
  • Differential diagnosis
  • Aquarium granuloma treatment
  • Prognosis aquarium granuloma
  • Complications
  • Tendonitis
  • Septic arthritis
  • Osteomyelitis
  • Prevention and prevention


What is an aquarium granuloma?

An aquarium granuloma, also called ‘swimming pool granuloma’, is a skin disorder caused by the bacterium Mycobacterium marinum . The bacterium mainly occurs in fresh water and has an optimal growth temperature at 25-30°C. Initially the condition was mainly observed in swimmers, but in recent years it has mainly been seen in aquarium keepers.


An aquarium granuloma is also known by the following names:

  • Aquagranuloma
  • Fish tank granuloma
  • Mycobacterium Marinum infection
  • fishbowl granuloma
  • pool granuloma


Causes of aquarium granuloma

In most cases, people become infected after minimal trauma to the skin (a crack or abrasion) and having come into contact with contaminated water, often after operations or work in an aquarium or swimming pool, in rivers or lakes. The condition usually manifests itself after 2 to 6 weeks.

Risk factors for pool granuloma

Risk factors that increase the occurrence of an aquarium granuloma due to Mycobacterium Marinum include:

  • exposure to swimming pools (as a swimmer or swimming instructor) that are insufficiently chlorinated
  • working or being exposed to salt or freshwater aquariums
  • coming into contact with marine animals (whether from oceans or rivers), such as fish, crustaceans, turtles
  • cleaning, processing or packaging fish
  • fishing as a hobby can also pose a risk of infection
  • to dive
  • any exposure to contaminated water
  • having a poor immune system


Incubation period

The incubation period is the time between infection with the pathogen and the appearance of disease symptoms. This is two to three weeks, but can vary from one week to two months.

Who gets it?

Anyone exposed to the bacteria Mycobacterium marinum is at risk for aquarium granuloma. It is equally common in men and women. An aquarium granuloma is a very rare infection; the estimated incidence is 0.27 cases per 100,000 persons

Aquarium granuloma / Source: CDC NIOSH, Wikimedia Commons (Public domain)

Symptoms of aquarium granuloma

The main symptom is a red, unclearly defined pustule or swelling, with a nodular border. It is often a solitary pustule or nodule, but more spots may also be present in the same skin area. The elbows, fingers and backs of the hands are the most commonly affected body parts. The knees and legs are less commonly affected. Over time, the affected area may become more plaque-like and ulcerated. The lymph nodes in the armpit may also be slightly enlarged (swollen lymph nodes).

Examination and diagnosis

Physical examination and skin biopsy

The skin abnormality has a striking clinical picture, which, together with the patient’s story, often makes the diagnosis easy. Sometimes a skin biopsy and skin culture is necessary because the symptoms of aquarium granulomas are sometimes reminiscent of the clinical picture of other skin conditions.

Differential diagnosis

There are a number of other (infectious) diseases that are very similar to aquarium granuloma:

  • psoriasis vulgaris;
  • chronic eczema;
  • dermatomycosis;
  • chronic discoid lupus erythematosus (CDLE);
  • stage III syphilis;
  • cutaneous lymphoma;
  • lupus vulgaris (cutaneous tuberculosis);
  • leprosy.

Because the skin abnormalities in aquarium granuloma can correspond to various skin diseases, additional research is often done by means of a culture for mycobacteria.

Freshwater aquarium / Source: User Aleš Tošovský, Wikimedia Commons (Public domain)

Aquarium granuloma treatment

Without treatment, the condition often heals within 1 to 2 years, leaving behind scars. Treatment is with antibiotics, usually doxycycline or clarithromycin, for 2 to 3 months. Sometimes it is necessary for the doctor to remove necrotic (dead) tissue through a surgical procedure, better known as a debridement.

Prognosis aquarium granuloma

Pool granulomas can usually be cured with antibiotics. However, it heals with scarring. However, individuals with suppressed immune systems are at increased risk for severe forms of the infection.


Occasionally joint or bone infections occur. The disease may last longer or become more complex in patients whose immune system does not function properly. Possible complications include:


Tendonitis (tenosynovitis or tendinitis) may occur. Tendons connect muscles and bones. The affected part of the tendon is then painful, tender and swollen.

Septic arthritis

In septic or infectious arthritis, the fluid and tissue of a joint are inflamed. The result is pain and swelling of the joints.


Osteomyelitis refers to an infection of the bone, bone marrow and periosteum caused by bacteria.

Prevention and prevention

Avoid contact with contaminated water. Wear gloves when cleaning aquariums, especially if the skin is damaged at all.

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