Reply To: Seahorse Fish TB

Pete Giwojna

Dear Seabreeeeeeze:

I suspect the reason that you don’t see much discussion or concern about piscine tuberculosis in the fish community is because the bacteria that can cause it can be found in virtually all bodies of water, not merely fish tanks, and because the risk is so low. It is possible to be exposed to this bacteria by taking a dip in a swimming pool, swimming at your local beach, going fishing at your favorite lake or stream, making a trip to your local fish store or aquarium shop, are even from tap water or well water. But it is very rare to become infected following such exposure, and it even in those exceedingly uncommon cases, the symptoms are typically very mild.

For example, here is an excerpt from my new book (Complete Guide to the Greater Seahorses in the Aquarium, unpublished) that discusses mycobacteriosis in more detail:


Mycobacteriosis is also known by the following synonyms: fish tuberculosis, piscine tuberculosis, granuloma disease, swimming pool granuloma, fish tank granuloma, and acid-fast disease (Aukes, 2004; Leddo, 2002a). Like all fishes, seahorses are susceptible to Mycobacteriosis. It is not uncommon in wild-caught seahorses obtained from pet stores and is the second most commonly seen bacterial infection of syngnathids at large public aquaria after Vibriosis (Bull and Mitchell, 2002, p20).


Fish tuberculosis is caused by pathogenic Mycobacteria, of which two different species are the primary culprits: Mycobacterium marinum and Mycobacterium fortuitum (Giwojna, Sep. 2003). Unlike most bacteria the plague fish, these Mycobacteria are gram-positive, and take the form of pleomorphic rods that are acid-fast and nonmotile (Aukes, 2004). When cultured on solid media, they form cream-colored to yellowish colonies (Aukes, 2004).

Mycobacteriosis is worldwide in distribution (Giwojna, Sep. 2003). All fish species are considered susceptible to it (Aukes, 2004). Although this disease can in fact infect almost all fish, certain species are more vulnerable than others (Giwojna, Sep. 2003). The most susceptible species are freshwater tropicals such as black mollies, all gouramis, neons and other tetras, all labyrinth air breathers, and most species of the Carp family (goldfish and koi, for example), Aukes, 2004.

Mycobacteria are ubiquitous and waterborne, and the aquatic environment is considered the disease reservoir for fish tuberculosis (Aukes, 2004). Mycobacterium marinum has been cultured throughout the world from swimming pools, beaches, natural streams, estuaries, lakes, tropical fish tanks, city tap water and well water (Aukes, 2004; Leddo, 2002a). Human epidemics of granulomatous skin disease have occurred from swimming in infected water, and in fact, this mode of human infection is far more common than infection from exposure to infected fish tanks (Aukes, 2004; Giwojna, Sep. 2003).

Clinical Signs:

There is a very severe or peracute form of this disease, in which fish can simply be found dead without showing any telltale signs or symptoms (Bull and Mitchell, 2002, p20), but that is quite rare. In my experience, Mycobacteriosis is a chronic disease that progresses quite slowly in aquarium fishes (Giwojna, Sep. 2003). It may take years for an infected fish to develop any symptoms of apparent illness and much longer before it becomes fatal (Aukes, 2004). The glacial progression of the disease makes it difficult to diagnose. Some early signs to look out for include lethargy, fin loss, emaciation, skin inflammation and ulceration, edema, popeye, and peritonitis (Aukes, 2004). There may be superficial skin lesions that take the form of small subdermal lumps or pus-filled nodules of granulation tissue (Bull and Mitchell, 2002, p21). These are simply the outward manifestations of a systemic infection that may already involve many of the major internal organs (Bull and Mitchell, 2002, p21). In later stages, nodules may develop in muscles or skeletal structure and deform the fish. (Giwojna, Sep. 2003).

As difficult as slow-moving TB may be to diagnose while the infected fish is alive, once the victim expires, postmortem examination will reveal clear, unmistakable signs of Mycobacteriosis (Giwojna, Sep. 2003). The telltale granulomas will appear as gray or white nodules in the liver, kidney, heart and/or spleen (Aukes, 2004). There is often black, necrotic tissue eating away at the internal organs, and there may also be skeletal deformities. Diagnosis is then confirmed by the presence of acid-fast bacteria in tissue sections (Giwojna, Sep. 2003).

Treatment and Control:

There is no practical method for treating mycobacteriosis or granuloma disease at the hobbyist level. As discussed below, good aquarium management can prevent mycobacteria/Nocardia from becoming problematic. Prevention is the watchword for this condition.


The bacteria can be transmitted through the water from open ulcers, through contaminated food (including live foods such as shrimp or molly fry), via feces of infected fish, or through the consumption of infected, dead or dying fish in the tank (although the latter does not apply to seahorses), Aukes, 2004.

Contributing factors:

This disease is not highly contagious and does not seem to spread from fish to fish readily (Aukes, 2004). However, fish TB it is often associated with poorly kept or dirty tanks with poor water quality (Aukes, 2004). Chronic stress from factors such as overcrowding, malnutrition, or aggressive tankmates often plays a role as well (Giwojna, Sep. 2003).

Mycobacterium, the causative organism, is believed to be ubiquitously present, making it very difficult to eliminate it entirely. However, if good aquarium maintenance and management is followed, including vacuuming of the gravel along with good filtration and regular water changes, combined with a nutritious diet and the addition of an enrichment product rich in vitamins, the problem can be minimized and eliminated as a cause of mortality (Aukes, 2004). Any dead fish should quickly be removed and disposed of properly. Diseased live fish should be isolated and treated in a hospital tank (Giwojna, Sep. 2003).

Transmission to Man:

The seahorse keeper should be aware that piscine tuberculosis is one of the few forms of fish disease that is communicable to humans (Leddo, 2002a). This transmission usually manifests itself as an unsightly skin rash involving one or more granulomas on the arms of the fish-keeper (Leddo, 2002a). In severe cases, these nodules of inflamed tissue can become large and disfiguring. They can spread and be very difficult to eliminate. The granulomas often take some 2-4 weeks after exposure before manifesting themselves, so the individual is frequently unaware of how he or she contracted them and the condition very often goes undiagnosed (Giwojna, Sep. 2003). The Mycobacteria that cause the disease typically gain entry through a break in the skin such as a cut, scrape, or abrasion on the hand or arm of the aquarist (Leddo, 2002a). Although unsightly, the granulomas themselves are not a serious problem and are almost always localized and most certainly curable in healthy individuals. But for those of us whose immune systems are compromised by AIDS, kidney disease, diabetes, liver dysfunction, chemotherapy or the like, the infection can sometimes become systemic or, on rare occasions, even life threatening (Giwojna, Sep. 2003).

Awareness is the appropriate response to the risk posed by fish tuberculosis. The seahorse keeper should be aware of the remote possibility of being exposed to Mycobacteria via his aquarium, and take appropriate precautions, but there is certainly no need to be overly concerned (Giwojna, Sep. 2003).

The aquarist should merely remain aware of Mycobacteria and follow the usual sensible precautions. Nets, aquarium accessories and equipment, and any other items that may come in contact with the fish should be sterilized between uses to prevent cross-contamination (Giwojna, Sep. 2003). Avoid mouth-siphoning of the water in a Myco-positive tank (use a hand pump instead). Mycobacterium cannot penetrate intact skin — it only causes infection after entering through open wounds or sores, so make full use of aquarium gloves and don’t place your hands or arms in the aquarium if you have any cuts or scrapes (Giwojna, Sep. 2003). Handle sick fish carefully, dispose of deceased specimens properly, and scrub up afterwards. Do NOT dispose of dead fish by flushing them down the toilet, as this is a prime way to spread disease. Place the fish carcass in a plastic bag or wrap it in some foil and dispose of it with the solid waste of the household. And don’t feed dying fish to larger carnivorous fish, since this an excellent way to spread infection (Giwojna, Sep. 2003).

One thing hobbyists who are worried about fish TB can do to allay their concerns is to get their seahorses and live foods (crustaceans such as shrimp are known vectors for Mycobacteriosis) from a High Health facility such as Ocean Rider rather than from their local fish store (Giwojna, Sep. 2003). Seahorses at OR are routinely screened for pathogens and parasites by independent examiners from an outside agency (DVMs with the Department of Agriculture), and I know for a fact that Mycobacteriosis is one of the diseases they specifically check for (Giwojna, Sep. 2003). Thus far, multi-organ histopathology has found no granulomas and tissue sections have revealed no acid-fast bacteria — conclusive proof that Ocean Riders are free of Mycobacteria. <Close quote>

That’s the rundown on mycobacteriosis or granuloma disease, Seabreeeeeeze. Take all due precautions to protect yourself when you are working in the aquarium and to prevent any spread of the infectious organisms to nearby aquaria. And you may want to consider installing an ultraviolet sterilizer on your seahorse tank as an added precaution.

Pete Giwojna, Ocean Rider Tech Support

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