Sores That Won't Heal After Tank Work: The Fish Tank Granuloma Risk
A small cut on the hand, a routine tank clean-up, and a few weeks later a reddish bump that won't heal: this scenario has a name, fish tank granuloma. A study by Slany, Jezek and Bodnarova published in 2013 in BioMed Research International (research on Google Scholar) details two cases of aquarists infected with Mycobacterium marinum, a bacterium naturally present in fresh and salt water worldwide. Find our other pointers in the care and grooming section and on the fishkeeping hub.
How does this bacterium infect an aquarist?
Mycobacterium marinum lives naturally in the water and on surfaces of an aquarium without posing any problem to healthy fish. The risk appears when a hand with a small cut, a scrape, or even a fish-spine prick stays in prolonged contact with tank water: the bacterium uses this opening to settle under the skin, most often on the fingers or the back of the hand.
Why is this type of infection sometimes misdiagnosed?
In the cases reported by this study, one patient was first treated for rheumatoid arthritis before the infectious origin was identified, which delayed proper treatment and let the bacterium spread deeper. The initial lesion often looks like a simple wart or a persistent pimple, with no fever or obvious sign of infection, which explains why it's rarely linked to the aquarium right away.
How can this risk be reduced day to day?
Wearing waterproof gloves for routine maintenance, especially when vacuuming the substrate or handling sharp decor, sharply limits direct contact between a wound and the water. Covering any existing cut with a waterproof bandage before putting hands in the tank remains the simplest and most effective step.
Should you worry about handling fish with an injured hand?
The risk also runs the other way: an injured hand handling a sick fish during a stint in a hospital tank multiplies opportunities for prolonged contact with water that may carry bacteria. Using a net rather than bare hands to catch a fish remains a useful habit regardless of any skin risk.
- Fish tank granuloma is a skin infection caused by a bacterium naturally present in aquarium water
- It mainly occurs when an existing wound stays in prolonged contact with tank water
- The lesion develops slowly and can be mistaken for other skin issues, delaying diagnosis
- Waterproof gloves and a sealed bandage over any cut noticeably reduce this risk
Frequently asked questions
Does this risk apply to all aquariums, including small home tanks?
Yes, the bacterium isn't tied to a particular type of aquarium: the risk mainly depends on contact between an open wound and the water, regardless of tank size.
Should a pimple that won't heal after tank maintenance be a concern?
A skin lesion that persists after contact with tank water warrants seeing a doctor and explicitly mentioning that exposure, since it makes diagnosis much easier.
Do chlorine or common cleaning products remove this risk?
No, the bacterium lives in the water of the stocked tank itself, which makes total elimination unrealistic; prevention mainly relies on protecting wounds rather than disinfecting the tank.
This guide is part of Planète Pets’s Fishkeeping universe. Our advice is general in nature: for any health concern, your veterinarian remains the only reference.