Fish Mycobacteriosis (Fish Tuberculosis): A Zoonotic Aquarium Disease
Fish mycobacteriosis is a chronic, hard-to-cure bacterial disease of aquarium fish caused by Mycobacterium marinum and relatives — and it can infect humans as 'fish tank granuloma'. Learn the clinical signs, the serious zoonotic risk to aquarists, and why biosecurity beats treatment.
The pathogen
Fish mycobacteriosis (fish tuberculosis) is caused by non-tuberculous mycobacteria — the slow-growing Mycobacterium marinum plus rapid-growing M. fortuitum and M. chelonae. M. marinum grows optimally at about 30°C and barely at 37°C, which is why in humans it prefers cooler peripheral tissue such as the hands.
Clinical signs in fish
It is a chronic granulomatous disease. Signs include uncoordinated swimming, abdominal swelling, progressive weight loss and emaciation, skin ulceration, fin and scale loss, spinal or skeletal deformity, and white nodules (granulomas) in the liver, kidney and spleen. Because it is chronic, losses accumulate slowly over months rather than in a sudden outbreak.
Why it is so hard to cure
There is no reliable cure in fish. Complete control of piscine mycobacteriosis may require destroying all affected stock and disinfecting the holding tanks; ethanol, lysol and sodium chlorite have been reported to destroy M. marinum. In humans, antibiotic courses (for example clarithromycin, ciprofloxacin, or ethambutol with rifampicin) have ranged from 1 to 25 months, with a median of about 3.5 months.
Management and biosecurity
- Quarantine all new fish and avoid mixing stock from unknown sources.
- Wear waterproof gloves for all tank work and cover any cuts.
- Assume there is no reliable cure — humanely cull affected fish rather than attempt treatment.
- Disinfect nets and equipment (ethanol, lysol or sodium chlorite) and avoid cross-contaminating other tanks.
- Seek medical advice promptly for any non-healing skin nodule after aquarium contact.
Sources: pmc.ncbi.nlm.nih.gov ; en.wikipedia.org (Wikipedia, CC BY-SA 4.0)