Re:Uroliths in dwarf seahorses

Pete Giwojna

Dear Bruce:

I am sorry to hear about the difficulties your dwarf seahorses (Hippocampus zosterae) have been experiencing recently. I have not seen uroliths and any of our specimens so I cannot offer any insights as to why they may be occurring in your population of dwarves.

But that would be an excellent question for you to pose to the "Syngnathidae" discussion group, which is composed of conservation biologists, public aquarium representatives, veterinarians, aquaculturists, fish curators and other aquarium professionals who work with syngnathids. You can contact the group at the following URL and they may have some useful information regarding uroliths in seahorses to share with you:

In addition, I would like to briefly address the ongoing issues with mycobacteria you mentioned that you are having throughout your seahorse system, sir. It is always a difficult situation to deal with when mycobacteriosis, also known as granuloma disease or piscine tuberculosis, appears in an aquarium system. The bacteria that cause the affliction are ubiquitous, present in almost all environments, and affect all types of fish to one degree or another.

First of all, I would just like to say that, in many cases, a diagnosis of mycobacteriosis is far from a death sentence so the situation may not be nearly as bleak as you are imagining. For one thing, the disease is not highly contagious and it does not spread from fish to fish readily, so even though all of your seahorses may have been exposed, some of the individuals may never develop granuloma disease. Even if they do, in many cases, mycobacteriosis or granuloma disease progresses very slowly and fish may live normal lives for many years before they show any signs of an illness, much less lose their lives to this condition. It is not uncommon for fish to live happily with mycobacteriosis all their lives and never show any clinical signs. (It’s kind of like prostate cancer in that regard, Dave. When a senior citizen is diagnosed with prostate cancer, very often they choose not to treat it because it is such a slow-growing cancer that it may take decades to become life-threatening, and the patient is very likely to die from natural causes due to some other condition well before the prostate cancer becomes problematic for them. In some instances, mycobacteria in seahorses presents a similar situation.)

For example, here is what Kathleen Alford, Curator at the Tennessee Aquarium, has to say about this affliction:

"There are no known treatments for mycobacterium outbreaks. The common thought is that most or all Syngnathids have this even in the wild but can live happily with it under optimum conditions. The best "fix" is to make sure that all parameters are in check: water quality, diet, population density, ect. We have several groups of seahorses that we know have mycobacterium but have been living with it for years. We also have groups of seahorses that have died or are dying off rapidly as the mycobacterium infestation gets worse and worse. Each group is different so my advice is to just make sure that all of your husbandry is optimum and the myco will play out as it will. Good Luck! "
Kathlina Alford
Tennessee Aquarium

In most of the public aquariums, when they have an outbreak of mycobacteriosis in an aquarium, they will typically just continue to maintain the fish in that tank as usual, concentrating on providing them with optimum water quality, and then take all due precautions to prevent from spreading the infection to nearby aquariums or to human hosts.

As you know, Dave, mycobacteriosis is one fish disease that can be passed on to human beings through cuts or scrapes in the skin, and you’ll need to take precautions to prevent that from happening.

For instance, here is what Paul Anderson of the Department of Fisheries and Aquatic Sciences at the University of Florida recommends to seahorse keepers with regard to mycobacteriosis:

"Fellow Seahorse Enthusiasts:

Mycobacterium is a genus of bacteria that are ubiquitous in almost all environments. Mycobacterium infections occur in many (if not all) vertebrate taxa (e.g., mammals, birds, fish, etc.). Some studies that have looked at prevalence of infection of Mycobacterium in wild animals have often found that a small percentage of wild animals are infected, even without clinical signs.

The most common Mycobacterium species found in seahorses are M. marinum, M. chelonae, and M. fortuitum. There is currently no cure for mycobacterium infections in fish. The options available are to 1) depopulate and disinfect the system, or 2) maintain the fish but prevent cross-contamination by observing strict biosecurity protocols. The second option is often chosen by public aquaria with long-standing displays, when aquaculture/production of the infected fish is not an issue.

Many mycobacterium spp. can cause disease in humans, especially if the species is a rapidly growing one and/or if the person is immunocompromised. Of the three species mentioned above, M. marinum is a slow grower, and grows at 25 degrees Celsius incubation, but not at 37 degrees Celsius. The other two are rapid-growing species and grow at both temperatures of incubation. The significance of 37 degrees is that it is human body temperature. While most infections of otherwise healthy people are limited to lesions on the extremities (even with infection by a rapid-grower), there is a greater risk of the rapid-growers to cause systemic disease (especially in immunocompromised people).

In a myco-positive tank, the best option is not to come in contact with water or fish; wear gloves (sleeved gloves if necessary). Avoid mouth siphoning (use a hand pump). Having said that, in an aquarium situation mycobacterium only causes infection if it enters a wound; it cannot penetrate intact skin. Effective disinfectants against mycobacterium include spraying with 70% Ethanol and allowing the equipment to air-dry, and bleach baths (I use 50ppm bleach baths with a minimum contact time of one hour, this has been reported to be effective against M. marinum) followed by sodium thiosulfate neutralization baths. Ultraviolet light sterilization is also recommended in myco-positive systems. If you’ve got myco-positive tanks among other systems, common sense suggests performing husbandry on these systems last in your rounds.

A note on ethanol: I have found in my experience that seahorses are very sensitive to ethanol, so I advise being very cautious to avoid overspray into tanks (while we’re on the topic, has anybody else observed this?)"

Check out the following for more information about mycobacterium infections in fish/aquaria:
Mainous, M.E., and S.A. Smith. 2005. Efficacy of common disinfectants against Mycobacterium marinum. Journal of Aquatic Animal Health 17: 284-288.

Paul Anderson
Ph.D. Candidate
Department of Fisheries and Aquatic Sciences
University of Florida

Finally, Dave, here is an excerpt from my new book (Complete Guide to the Greater Seahorses in the Aquarium, TFH Publications, 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, Dave. I would concentrate on maintaining optimum water quality in your seahorse system, provide them with good nutrition, and practice sound aquarium management and fish husbandry, and the rest of your seahorses may well remain unaffected or live long lives with no clinical signs that there were ever exposed to the Mycobacteria. 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.

Best wishes with all your fishes, Dave!

Pete Giwojna

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