Mycobacterium piscium

From Fish
Unstained wet mount of gill tissue showing a granuloma that was associated with a systemic Mycobacterium infection, 100X. Courtesy of Dr. Ruth Francis-Floyd
Granulomatous lesions typical of Mycobacterium in a fancy goldfish. Courtesy of Dr. Ruth Francis-Floyd

Bataillon et al (1897) were the first to record tuberculosis in a carp (Cyprinus carpio) in waters contaminated by a person with TB[1].


The causative bacteria can be any number of species of Mycobacterium, including M. piscium, M. marinum, and M. fortuitum. These gram-positive, acid-fast, non-motile bacteria are difficult to grow but can be isolated using Lowenstein-Jensen media following incubation at 25°C for 3-4 wk.

Predisposing environmental factors include low dissolved oxygen, low pH, and high organic load, all of which are found in recirculating aquaculture systems.

Clinical signs

Fish infected with tuberculosis may become hollow bellied, pale, show skin ulcers and frayed fins, and loss of appetite. Yellowish or darker nodules may appear on the body or eyes. The main cause for this disease appears to be over crowding in unkempt conditions[2].


A presumptive diagnosis is based on visualization of acid-fast rods in granulomatous material from suspect lesions. Definitive diagnosis requires isolating and identifying the bacteria. Because the disease can produce skin lesions and an allergic dermatitis in humans, and because treatment does not eliminate the disease, infected fish are usually destroyed.


There is no specific antimicrobial therapy for eradication of this hardy bacteria, and the zoonotic risk implies it be eradicated effectively.

Aquarists should be informed of potential risks if handling or cleaning contaminated fish or exhibits. An aquarium should be disinfected before other fish are added. Mycobacteria are not always killed by bleach; disinfection with alcohol or phenolic compounds is recommended.


  1. Bataillon, E & Terre, L (1897) La form saprophytique de la tuberculose humaine et de la tuberculose aviare. Comp Rend 124:1399-1400
  2. Merck Veterinary Manual