Symptoms
Wasting — fish eats but loses weight over months. Spinal curvature, pineconing, ulcers that will not heal.
Pop-eye, lethargy, bloating. Often one fish at a time, slowly.
Source
Most pet store guppies carry low-level mycobacterium. Stressed fish develop active infection.
Contaminated live foods (especially tubifex worms) are another common source.
No Real Cure
Kanamycin helps some cases but most do not recover.
Euthanize severely affected fish to protect the rest.
Zoonotic Risk
Fish TB can infect humans through open cuts — causes "fish handler disease," skin granulomas.
Always wear gloves or wash immediately after tank work. Never put your hand in a tank with open cuts.