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systemic bacterial

Fish tuberculosis (Mycobacterium)

Chronic, progressive wasting with a combination of sunken belly, spinal deformity (bent spine), skin ulcers, and color loss. Caused by Mycobacterium marinum or related species. Incurable, highly persistent in tank environments, and importantly can cause skin infections in humans. Handle affected fish and their tank water with care.

High prioritypattern match not diagnosis2 source notes

Do first

  • Do not handle tank water or fish with open cuts or wounds on your hands Mycobacterium marinum causes fish tank granuloma in humans.
  • Use gloves when working in any tank where fish TB is suspected.
  • Isolate affected fish humane euthanasia is often the kindest and most practical option.
  • Do not sell, trade, or rehome fish from a suspected TB tank.
  • Consider a full tank breakdown and disinfection Mycobacterium is extremely persistent in aquarium substrate and equipment.

Escalate if

  • Any human household members develop persistent skin lesions or nodules after contact with the tank refer to a physician immediately (fish tank granuloma is a reportable condition).
  • Multiple fish over the course of months all dying of progressive wasting with ulcers and curved spines.
  • Outbreak in a public aquarium or store professional veterinary involvement is needed.

Water clues

These readings can push this pattern higher or lower in the triage result.

ammonia above zero+2

Chronic poor water quality is associated with Mycobacterium outbreaks but the presence of ammonia alone does not indicate TB.

nitrate above 80+2

Long-term high nitrate is associated with immune suppression that may allow Mycobacterium to establish.

Care protocol

Follow only the steps that fit your species, tank inhabitants, and medication label.

Identifying fish TB

  1. Fish TB presents insidiously affected fish show progressive wasting over weeks to months.
  2. Key signs: sunken belly despite eating (or reduced eating), spinal curvature or deformity, non-healing ulcers on the body, popped eyes.
  3. Other diseases must be ruled out first fish TB is a diagnosis of exclusion in most hobby settings.
  4. Definitive diagnosis requires laboratory culture or histopathology not available to most hobbyists.
  5. If multiple fish in a mature tank have died of unresolvable progressive wasting over months, Mycobacterium should be on the differential list.
Cautions
  • Do not confuse with wasting from parasites, poor diet, or other bacterial infections. These are far more common.
  • Fish TB is often overdiagnosed by hobbyists exhaust other explanations first.

Tank disinfection after confirmed outbreak

  1. Humanely euthanize all fish that have been in the infected tank.
  2. Discard all porous materials (substrate, rocks with crevices, sponge filter media) Mycobacterium is nearly impossible to disinfect from these.
  3. Disinfect the tank, heater, filter housing, and glass with a 10% bleach solution for 30 minutes, then rinse thoroughly and allow to air-dry for 48 hours.
  4. Cycle the tank fresh before adding new fish.
Cautions
  • Do not try to keep and treat fish in a confirmed Mycobacterium tank it rarely succeeds and extends the human health risk.
  • Inform any previous buyers of fish from this tank if an outbreak is confirmed.

Source notes

References and context notes used for this triage entry.

Mycobacterium marinum CDC fish tank granulomaCDC reference for human health aspects of Mycobacterium marinum.Mycobacteriosis in fish Merck Vet ManualVeterinary reference for mycobacteriosis in aquarium fish.
Run Symptom CheckerCompare this pattern against water readings, affected count, and recent tank context.Ask AdvisorUse TankFlare Advisor to review this against your saved tank and recent logs.

Related patterns

Similar symptoms or risk factors worth comparing before treatment.

UrgentBacterial septicemia (hemorrhagic septicemia)

Red streaking, hemorrhaging under the skin, and systemic illness caused by gram-negative bacteria (most commonly Aeromonas hydrophila) entering the bloodstream. Can follow injury, fin rot, poor water quality, or be primary in severely stressed fish. A systemic emergency.

UrgentUronema marinum (marine ciliate)

A scavenger ciliate that becomes pathogenic under poor water quality or stress, causing rapidly spreading open lesions, internal hemorrhaging, and fast death in marine fish. Fish appear to melt. Uronema is most dangerous to thin-bodied fish (chromis, small wrasses, clownfish) and is often introduced with uncleaned live rock or wild-caught fish. Notoriously difficult to treat.

High priorityNeon tetra disease (Pleistophora hyphessobryconis)

Progressive color loss (the neon-blue stripe fades or turns white in patches), body deformity, and wasting in small tetras and related species. Caused by the microsporidian parasite Pleistophora. Highly contagious, incurable, and almost always fatal affected fish should be humanely euthanized and removed promptly.

Medium priorityChronic stress syndrome and immune suppression

A fish that is persistently stressed over weeks or months will develop a suppressed immune system, making it vulnerable to infections that healthy fish would fight off. Chronic stress is itself a disease state that produces predictable signs and predisposes fish to virtually every other condition in this catalog. Identifying and removing the stressor is the only effective treatment.