The information provided here is for educational purposes only. You should seek the advice of medical professionals if you believe you have been exposed to Mycobacterium marinum. Only your doctor can correctly diagnose this condition and recommend an appropriate course of treatment. It is only my intention to make you aware of the dangers, suggest a few simple protective measures, and to encourage you to seek medical attention with this disease in mind if you suffer from any suspect skin conditions.

Cryptocaryon. Amblyoodinium. Brooklynella. You are all probably familiar with these fish diseases, but are you aware of the dangers that Mycobacterium marinum poses to your fish and, more importantly, you? Never heard of it? How about fish tuberculosis, piscine TB, fish tank granuloma, or possibly swimming pool nodules? These are all common names for somewhat uncommon ailments caused by Mycobacterium marinum. You might recognize from the genus, that Mycobacterium marinum is a distant relative to the organism that causes tuberculosis in humans.

Fish Infections of Mycobacterium marinum

Mycobacterium marinum causes a chronic progressive fish disease found in freshwater, saltwater, and brackish environments. Weight loss, non-healing open ulcers, a distended abdomen, loss of appetite, fin erosion, unusual coloration, pop-eye, spinal deformities, and listless behavior are all possible signs of infection. Unfortunately, it is also possible an infected fish will show no external signs and may die mysteriously. A post-mortem examination will reveal the telltale nodules on and in the internal organs; in particular, the kidney, spleen, and liver.

Closed aquatic systems with a high density of fish and warm waters (Hint, hint; this is another way of saying your average everyday home aquarium) appear to be conditions particularly favorable to this infectious agent. Poor overall water quality and various nutritional deficiencies have also been implicated as possible contributing factors to the onset of this pathogen. Good husbandry practices such as strict quarantine protocols, a high-quality and varied diet, as well as regular cleanings can help to keep your aquarium free of this bacterium, but unfortunately it is no guarantee. Mycobacterium can be found in soil samples and frankly just about any puddle of water, including swimming pools that are improperly sanitized. Consequently, it would be wise to assume it is always present in your aquarium and appropriate protective measures should be taken.

Sterilizing a tank is not usually effective since re-infection is so likely. It is also unpractical for our reef aquaria. To properly sterilize a tank, you must treat everything with bleach: aquarium, plumbing, pumps, filters, live rock, sand, corals, etc. I doubt this is a measure that many reef aquarists would want to undertake. There was even one documented case of a group of Egyptian spiny-tailed lizards, Uromastyx aegyptius, contracting Mycobacterium marinum because they were housed in an enclosure that was once used for fish (Morales, Dunker 2001). The tank was stored completely dry, but un-sterilized, for some time, and this bacterium managed to survive and infect the reptiles. This goes to show how truly resilient this pathogen is, and how extreme sterilization methods must be undertaken to be effective. The best protection for your fish against this disease is to keep them as healthy as possible and, therefore, keep their immune system operating in peak condition. As alluded to above, regular water changes with removal of dirt and detritus, closely monitoring the specifics as well as general trends in water quality parameters, and nutritious foods can all be helpful in prevention.

Obviously, sick or dying fish should be removed from the display tank and placed in a proper isolated quarantine tank or euthanized. Healthy fish feeding off of diseased ones is a primary means of transmitting the infection. Carbon dioxide poisoning and freezing are two commonly used, allegedly humane methods to put a fish down, but neither will kill this bacteria. If you choose to euthanize the fish, please dispose of the carcasses safely. Treating the bodies with bleach and subsequently disposing of them in the trash minimizes the risk of spreading a particularly virulent or antibiotic resistant strain as compared to flushing.

If you don't want to give up on a particular specimen, there are a few treatments that can be attempted, although none have been proven effective. Rifampicin, erythromycin, streptomycin, kanamycin, and minocycline have all been reported with varying degrees of success to combat this disease. These antibiotics need to be administered daily in the food for a minimum of one month, perhaps for as long as three months. At the same time, the use of ozone and/or ultraviolet sterilization may aid in controlling the spread of this disease. If you are serious, you should consult with a veterinarian trained in treating fish to come up with a specific course of treatment.


Keeping your fishes disease-free is one thing, but I am more concerned that you keep yourself disease free. Having had this infection once myself, I can tell you it is absolutely no fun, and one should try to avoid it at all costs. The simplest, most effective thing you can do is to keep your hands out of the tank as much as possible. Far too many hobbyists are in their tanks too often monkeying around with things; moving live rock around because the aquascaping does not look quite right, rebuilding because of avalanches, or adjusting the positioning of your corals because the polyp extension or coloration is not what was expected or desired. It is, quite simply, good aquarium practice to minimize having your hands in the tank. Magnet cleaners, long-handled algae scrapers, aquarium tongs, and various other grabbing devices are quite useful in minimizing human contact with the water.

Even when using all the tools available, occasionally it is still necessary to put your hands in the aquarium. For these instances, I strongly urge using a good pair of gloves. I have tried several different models marketed for aquarium use, as well as a few I picked up from veterinarian supply places and cleaning goods distributors, yet I keep coming back to a pair sold by Coralife. They are shoulder length, so they keep your entire arm dry and are thick enough so they don't tear easily, yet have a reasonable sense of feel. The only problem that I have found with them is they have a seam at the wrist, which seems to eventually leak. I own an aquarium maintenance business. On average I will service two to four different tanks per day five days per week. The Coralife gloves last me anywhere from three to six months before needing to be replaced. Given that will likely be used less often, I would imagine they would last a casual hobbyist considerably longer.

The last preventative measure is one you should all know well from Kindergarten: wash your hands! Washing with warm water and an antibiotic soap for 30-60 seconds can be especially helpful in keeping the aquarist from becoming infected. I recommend washing your hands immediately after coming into contact with any aquarium water and even when wearing gloves, just in case there was a small leak that went unnoticed.

Human Infections of Mycobacterium marinum

In humans, the two most common manifestations of this infection are a single large granuloma or an ascending lymphangitic granuloma (a series of smaller nodules usually starting on the dominant hand and progressing in a line up the arm). Less commonly seen is an infection in the joints, which will cause arthritis-type symptoms. This latter type of deep infection is associated with a puncture, like that from the spiny ray of a catfish or from a deep, open wound that becomes infected. Lastly, there is a rare case of a disseminating disease seen in immuno-compromised individuals that can be fatal. People diagnosed with HIV or AIDS, cancer patients undergoing chemotherapy, or any other person with a known immune system problem should be particularly careful. If you fall into any one of these categories, you may want to consider hiring a service company to take care of your tank. Also note that symptoms can wait to present themselves from two weeks to four months after initial exposure, due to the slow growth rate of this bacterium. Keep a close eye on any open cuts for that same time frame to ensure they heal properly and are not subject to infection.

A Couple of Case Studies

My good friend Don Tuttle, who is an accomplished aquarist with over 50 tanks in his house, incurred a minor cut on his right middle finger. He did not think anything of it and cared for it like any minor scrape. He washed it and applied a bandage. Several weeks later he noticed some swelling in the area, so he went to his doctor. This is the scariest part of this disease. So often it is misdiagnosed. Most physicians rarely see Mycobacterium marinum. It also cultures poorly, taking 4-6 weeks for a definitive test. Nothing specific will show up on either an X-Ray or blood work, except perhaps a weakly positive test for Tuberculosis. Poor Don went through several doctors and specialists. All of which were unable to figure out what was wrong with him. All the while his finger continued to swell to the point of discomfort. His doctors were seriously considering amputation when during a little bit of small talk Don mentioned something about his fish tanks. It was this little bit of information that triggered a correct diagnosis and saved Don's finger. He still had to go through surgery to remove the single large granuloma of Mycobacterium marinum that had formed as well as continue the subsequent antibiotic treatments. The pictures of his finger after his procedure showing the incisions that were made, how enlarged his finger still was, and the mass of nodules that were removed, are seen below.

About a year after Don went through his bout, I noticed a small bump on my right pinky finger knuckle. It looked somewhat like an ingrown hair at first. I covered it with a bandage and used an antibiotic ointment for one week and it seemed to disappear. However, it reappeared later, this time slightly larger and more dry and scaly. Because I remembered what Don went through, when it came back, I went straight to my Primary Care Physician and told him I was concerned that I had a Mycobacterium marinum infection. He referred me to a Dermatologist for treatment. Some time had passed between getting an appointment with my own doctor, having the referral clear the HMO, and then finally getting to see the specialist. By the time I saw the Dermatologist, my single bump had become an ascending lymphangitic granuloma, with a second bump at mid-forearm and a third just short of my elbow. The doctor confirmed my suspicions and prescribed an antibiotic. I ended up going through three different prescriptions before we found one my body could tolerate. I was prescribed a large dose of a strong antibiotic twice a day for three months. This cured me of the Mycobacterium marinum infection, but caused a whole new problem. While my actual encounter with Mycobacterium marinum was relatively harmless, I am still getting over the long-term effects of the cure. The long course of strong antibiotics absolutely wrecked my digestive system, and I am still suffering with minor difficulties to this day.

Please be careful. This disease is sort of the "dirty little secret" of the ornamental fish industry. It is not often discussed with the casual aquarist when getting their first 10-gallon starter tank, but it is a real danger, although admittedly rare. They are many other dangers in our aquariums that I did not cover in this article, too; envenomation from fish like Lionfish and Foxfaces, anaphylactive shock from repeated contact with Cnidarians, Vibrio infections, stings from Fireworms, getting stuck by a Sea Urchin, etc. The good news is that all of these can be combated with the same simple precautions mentioned previously in this article. Mobile tech deals and services are convenient to find in Vodacom specials. If you follow these guidelines, you can remain relatively safe from harm and continue to enjoy the beauty of this hobby.

If you have any questions about this article, please visit my author forum on Reef Central.


Andrews, Dr. Chris, Adrian Exell, and Dr. Neville Carrington. 1988. The Manual of Fish Health. Blacksburg, VA: Tetra Press.

Bassleer, Gerald. 1996. Diseases in Marine Aquarium Fish: Causes, Symptoms, Treatment. Westmeerbeek, Belgium: Bassleer Biofish.

Coulson, Dr. Ian. 1993. "TB or not TB?" Practical Fishkeeping, July 1993.

Dixon, Dr. Beverly. Personal Communications.

Fatherree, James. 2002. "Saltwater Nasties in your Aquarium." Tropical Fish Hobbyist, November 2002.

Gratzek, Dr. John B., Dr. Richard E. Wolke, Dr. Emmett B. Shotts Jr., Dr. Donald Dawe, and George C. Blasiola. 1992. Aquariology: Fish Diseases & Water Chemistry. Blacksburg, VA: Tetra Press.

Noga, Edward J. 2000. Fish Disease: Diagnosis and Treatment. Ames, IA: Iowa State University Press.

Untergasser, Dieter. 1989. Handbook of Fish Diseases. Neptune, NJ: TFH Publications.

Verneris, Michael. 1995. "A Word of Warning." Aquarium Fish Magazine, August 1995.

Useful Links:

Mycobacterium marinum Fact Sheet

Mycobacterium marinum Infection of the Skin

A Case Report of Mycobacterium marinum Infection of the Hand

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Mycobacterium marinum: The Fish Disease You Could Catch-