Symptoms Timeline
Early (months 1-3): slight weight loss despite normal eating. Mid (months 4-6): scale flaking, pale body, lethargy. Late (months 7+): spine curvature, open ulcers, eye bulging.
Fish often die 1-2 years after infection. Tank mates are usually infected by the time symptoms appear.
Diagnosis Is Hard
No easy in-tank test exists. Definitive diagnosis requires necropsy and microscopy for acid-fast bacteria. Most hobbyists diagnose based on symptoms and history.
If you see 2-3 symptoms (weight loss + spine curve + ulcer), assume fish TB and act.
Biosecurity Response
Cull and bury affected fish — do not flush. Bleach all equipment with 1:10 bleach solution for 30 minutes, rinse thoroughly.
Consider tank-wide euthanasia if multiple fish show symptoms. Restart after thorough disinfection and 30-day dry period.
Human Safety
Wear gloves when handling sick fish or dirty filter media. Open cuts + tank water = skin granuloma (fish handler's disease).
If you develop a persistent skin lesion on hands or arms that doesn't heal in 2 weeks, see a doctor and mention fishkeeping.