Gill Flukes

Gill Flukes


By Jim E. Quarles

These creatures are the number one problem encountered when keeping discus and angelfish. I can safely state that sooner or later, and generally sooner anyone who keeps discus fish will be the unwelcome host to these killers. Let me state something at the outset of this article. These parasites love a dirty tank, with the inside of the glass coated with fish slime that is not wiped off when water changes are made. It gives them a perfect place to hang on or deposit eggs to hatch and climb aboard your fish as they swim by.


The answer to that question begs other questions, like how do you know if your fish are suffering from gill flukes? And also few realize what a problem it is until they start losing fish or the fish become so weak that other diseases manifest themselves and mask the gill infections. Knowing when you have the parasites on your fish it is much easier if you have even a low power microscope or even a hand held lens that allows you to take a close look at the gills or scrapings from them. If you don't have a microscope, you must rely on your naked eye to tell you if the fish show signs of gill flukes. This is the hard way to become aware of the problem, but there are reliable signs that can tip you off to the onset of the parasitic infestation. Upon close examination you will note a discoloration of the gills, they will become pink, they should always be bright red. Off colored gill filaments are a sign of disease. Dactylogyrus spp, on gill filaments Photo credit to Tetra Press


In the past an enormous range of chemicals were used to treat external Parasites. But one draw back must always be kept in mind when applying any treatment. Certain chemicals will reduce or kill your filter bed or system. Treatment is a trade off when damaging chemicals are employed. Below are named a few of many chemicals or compounds that have been used, I will not note the dosages except in one case, if you elect to use any treatment full dosages should be clearly understood and their expected effects before treatment is started.

Formalin, formaldehyde, gas in water. Be careful, this is nasty stuff. Malachite Green, this is a dye that is active against a wide range of external parasites. It must be zinc free. Malachite green with Formalin. Again, be careful, this is a dangerous chemical. Another chemical commonly used is copper, but some fish are super sensitive to copper and testing must be done to make sure only the proper dosage is applied over time to the water. Fairly recently a new drug has become available to the discus hobbyist to help control gill flukes and other types of parasites. Praziquantel, currently sold under the trade name Droncit among other names, will quickly rid you of these parasites, and it appears to have little or no effect on the bio-filters in use at the same time. Discus, by test can withstand fairly heavy doses of Praququantel with no lasting or harmful affects. I recommend 3 to 4 ppm mixed in water for a first treatment, and this should be repeated on a regular bases and become part of your discus house keeping.

Oh yes, one final note. Praququantel or droncit, is not F.D.A. approved for the treatment of fish. However like a lot of other under the counter drugs you will find little problem obtaining it.

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