Fish Tuberculosis: symptoms, treatment, prevention

Mycobacterium marinum and related species cause a chronic systemic acid-fast bacterial infection in fish that is also zoonotic to humans.

Overview

Fish Tuberculosis is caused by Mycobacterium marinum and other Mycobacterium species. It is a chronic, slowly progressing infection that produces systemic granulomas. The disease is zoonotic: humans handling infected water with cuts can develop persistent skin granulomas, so biosecurity is essential.

Symptoms

Progressive emaciation
Spinal deformity
Skin ulcers and nodules
Loss of color
Popeye
Chronic ongoing mortality in the tank

Causes

Infection enters with carrier fish, contaminated water and shared equipment. Wild-caught feeders and biofilm in old systems are common reservoirs; once established, the bacterium persists in silicone joints and substrate.

Diagnosis

A long-running pattern of chronic wasting, spinal deformity and irregular ulcers in a tank is highly suggestive. Confirmation requires acid-fast staining and culture from internal organs by a veterinarian; rule out chronic Aeromonas and nutritional deficiencies.

Treatment

There is no consistent cure. The realistic approach is biosecurity: humanely cull symptomatic fish, disinfect the system, and prevent transfer to other tanks and to humans.

Quarantine

Symptomatic fish should never be moved between tanks; treat the entire affected system as contaminated and isolate equipment to it permanently.

Medication

No reliable medical cure. Humanely euthanise symptomatic fish to limit spread.
Disinfect tank and hardware with chlorine at 200 ppm for 1 hour, replace silicone seals and use strong UV; substrate should be discarded.
Wear waterproof gloves when handling water or fish, especially with any cuts on the hands.

Recovery

After depopulation and disinfection, restart the system from scratch and observe a long quiet period before reintroducing fish. Any surviving fish from the original system should be considered carriers.

Prevention

Wear waterproof gloves when you have any cuts
Long-term quarantine of new fish
Avoid wild-caught feeder fish
Do not move equipment between tanks
Depopulate chronically affected tanks