Flukes, Diagnosis and Treatment Options

Flukes belong to the phylum, Platyhelminthes, which literally means, flat worm. Flukes are further identified as monogenean trematodes, which describes their biological classification (trematodes) and the fact that they only need one host to complete their life cycle (monogenean).

When many people hear the term flatworm, planaria come to mind. Planaria are a harmless, non-parasitic cousin to the fluke. Flukes are a parasite that can quickly harm and even kill your fish. They act quickly and indiscriminately. People can even get them from eating uncooked/undercooked fish. Oddly enough, people are the root of the problem. Eggs of the fluke live in feces from infected humans. When those feces get into the water, the fish eat the eggs, the flukes hatch, people eat the fish and the whole cycle keeps going and going and going.

Fluke outbreaks in aquariums are most commonly caused by poor water conditions, stress and/or overcrowding. They can also be brought in on new fish; which is one reason why you are strongly advised to quarantine all new fish before introducing them to your aquarium.

In some cases, in early infestation, flukes can be observed with the naked eye on the skin of the fish, but as the outbreak worsens, the fish quickly creates massive amounts of slime in a vain attempt to neutralize the parasite. The slime then covers the flukes so that it is virtually impossible to see them individually. As such, the only certain way to identify a fluke infestation is with a skin scraping or gill biopsy then viewed under a microscope. A smear with something like a Q -Tip rubbed gently over the body of the fish, (holding fish carefully but gently in a wet net), then applying the smear to a clean microscope slide, should enable the user, even with a good magnifying glass, in the event that a microscope is not available, to make a certain diagnosis.

There are two main types of flukes that might be lurking on or in your fish. They are skin flukes (Gyrodactylus) and gill flukes (Dactylogyrus). Although Gyrodactylus and Dactylogyrus are classified as skin and gill flukes respectively, they don’t live exclusively in these areas and flukes of either type may be found at either area. Gyrodactylids differ from dactylogyrids in that Gyrodactylus has a v-shaped head, no eyespots and is viviparous (live-bearing), whereas Dactylogyrus has a scalloped head, distinct eyespots and is oviparous (egg-laying), however, both have an array of hooks at one end of their body which they use to anchor themselves to the fish and to move around. Once attached, the flukes constantly feed on the fish. Because gyrodactylids are live-bearing, this type of fluke reproduces at an alarming rate. It is possible for the mother to have a nearly fully developed young one inside her that has yet another one growing inside it. Because of this possible three generations in one, populations of flukes can double every 24 hours. Quick intervention is critical.

The symptoms of a fluke infestation are easy to recognize if you know what to look for. Initially there will be rubbing and flashing. You may also see circular shaped lesions, hemorrhages or ulcers as well as excessive slime/mucous. As the infestation progresses, you will see breathing difficulties, rapid gill movement, breathing at the surface or just stationary "hanging" at the surface. The fish will become lethargic and will eventually isolate itself and spend long periods of time resting on the bottom with clamped fins. You may also see loss of color and/or rapid weight loss. The fish will appear to be just wasting away. Many times, symptoms of a fluke infestation will be mistaken as a bacterial infection, but, parasitic infestations can cause necrotic damage, so a secondary bacterial infection and/or fungus may, nevertheless, occur. It has even been suggested that the parasites themselves may carry the infectious bacterium from fish to fish, so it is sometimes wise to treat for a bacterial infection as well as the flukes.

There are many treatment options for flukes, the easiest being salt dips. Consecutive treatments over 2-3 days will usually knock out any flukes living on your fish. The only trouble with these dips is that it only affects the flukes on your fish, not the eggs and larvae in your tank. Depending on the intensity of the infestation, you may be able to kill the adults, eggs and larvae in your tank by treating the entire tank with a salt solution of 0.1% - to 0.3% for a period of 2–4 weeks and/or pure praziquantel, also known as “prazi,” for 5-7 days with repeated treatments if necessary; however, if you have a heavy infestation, you may need to use potassium permanganate or take other measures to sterilize your entire tank. If complete sterilization of the entire tank is required, you will need to remove the fish from the infected tank until it has been sterilized and the fish has gone through 2-3 days of salt dips and/or other treatments so that you are certain the fish is healthy and fluke-free. A treatment of malachite and formalin may also be effective in combating flukes, but higher doses are most generally needed in order to be effective. Fluke-tabs are also effective in treating flukes. They contain organophosphates, which are effective in killing flukes, but flukes eventually build up a resistance to them. Fluke-tabs should not be used on Discus and Catfish as they are toxic to those types of fish. Great care should also be exercised when using them on Goldfish and Koi. Quite often these types of fish will experience an inflammatory dermatitis if the medicine is left in the water for over 48 hours. When using this treatment on Koi and Goldfish it is recommended that you do a 50% water change after 48 hours, wait 24 hours and then re-treat.

Sometimes, and in more advanced cases, flukes can migrate and/or cause damage to deeper internal parts of the fish’s body. Thus, it may also be a good idea to feed the fish, as prescribed on the bottle, with a medicated anti-parasite food that contains prazi.

With enough determination, beating skin flukes is relatively easy; however, the same can't always be said for gill flukes. Because of gill hyperplasia (swelling/enlargement) and increased mucous, gill flukes are often more protected from salt or chemical treatments, which is another reason to feed medicated food. The earlier you catch flukes, the easier it will be to get rid of them. Early detection is the key! You should also protect yourself; never eat raw or undercooked fish, especially if it comes from Asia where an estimated 30 million people are infected. Although medical treatments are available, the host may suffer permanent damage to the liver and bile ducts. If left untreated, death may occur.


Updated by Lynda Von G