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Ask a Veterinarian: Syndrome common in aquarium fish


© St. Petersburg Times,
published October 29, 2001

Question: I wrote to you before about my 30-gallon saltwater aquarium with two regal tangs sick with "ich." My fish got over this parasite when I followed your advice.

After the cure, I added another adult regal tang. Recently one of the original two adults came down with what the aquarium store people called "hole-in-the head" disease.

I called the advice doctor's office and found he had moved out of town. Since there appear to be no other veterinarians in this area trained in fish medicine, could you possibly tell me about this illness?

I check the water quality of the tank all the time and, except for a high nitrate level, which is controlled by large water changes twice a month, I think it is good.

If this is an infection, shouldn't the other fish be sick too?

Answer: It is difficult at present to find private practice veterinarians trained in fish medicine, but they are becoming more common. For now, people usually rely on the expertise of knowledgeable aquarium store dealers.

Marine (saltwater) hole-in-the-head syndrome is also called marine head and lateral line erosion syndrome, or MHLLES. It is perhaps the most common chronic disease of marine aquarium fish, especially tangs and angelfish. The disease has also been seen in butterfly fish, groupers, damsels and other species.

It usually starts as pinpoint holes around both sides of the face and eyes and may gradually expand in size and depth. The surface area involved may enlarge and include areas of color loss and fading from erosion on the face, around the eyes and on the flanks of the fish.

Severely affected fish may eat and behave normally, but some will darken and loose weight. Over time, they can become more susceptible to various diseases including secondary bacterial infections. If the condition is not reversed the fish will die.

The precise cause of the syndrome is unknown. More than one factor may be involved.

Development of the syndrome has been associated with nutritional deficiencies, particularly of vitamin C and A; stray voltage from improperly grounded electrical equipment, water quality problems such as very high nitrates, copper treatments, lack of natural sunlight and a virus. There is strong consensus that nutrition is a very important contributing factor.

The University of Florida is studying the nutrition of surgeonfish in the Florida Keys, a fish in the same general family as regal tangs, and this study may help uncover the causes of and lead to treatments for the syndrome.

In the meantime, be sure your fish are getting a variety of foods. Tangs are generally herbivorous (plant eaters). Their natural diet consists of algae and seaweed but also includes tiny animals found on coral reefs such as sponges.

Offer such fresh vegetables in their diet as romaine lettuce, broccoli and kale. Commercial natural dried seaweed (macroalgae) foods are available and are worth trying as a supplement.

Vitamin supplements placed in the water are probably ineffective. Buy only small amounts of fish food. Never keep fish food more than two months; two to four weeks is better.

Keep nitrate levels at fewer than 25 parts per million.

Avoid overfeeding and overstocking. A safe rule of thumb is to allow 1 inch of fish for each 3 gallons of available water.

Adult regal tangs are about 6 inches each, which means you probably have 18 inches of fish in your tank. Your 30-gallon tank's safety capacity is about 10 inches of fish. The excess 8 inches of livestock probably accounts for your high nitrate levels.

Consider a larger tank for these three fish. Locate it in an area with some direct sunlight, which will encourage algae growth, but don't allow sunlight exposure to unduly raise the tank temperature or cause excess algae growth.

The fish will graze on the algae, and there have been reports of disease reversals from such activity.

- Ruth Francis-Floyd, M.S., D.V.M., diplomate, American College of Zoological Medicine, University of Florida, Large Animal Clinical Sciences, Fisheries and Aquatic Science, Gainesville

-- Dr. Bruce Kaplan is a veterinarian editor/writer. Please send questions to Ask a Veterinarian, Pinellas Animal Foundation, P.O. Box 47771, St. Petersburg, FL 33743-7771. Because of the volume of mail, personal replies are not possible. Questions of general interest will be answered in the column.

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