Mastering Freshwater Aquarium Ecosystems
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Fish Health (Cont.)

Organophosphates like trichlorfon can be used to kill gill and skin flukes.

Formalin can be used to treat flukes. If treating gill flukes, it will typically require three days of treatment followed by a three day break, then three more days of treatment to kill any that have hatched from eggs. Some fish are sensitive to formalin.

Baths in medicated water are not an effective way to eliminate flukes. The aquarium system must be treated to eliminate gill or skin flukes that may not be attached to fish.

Tapeworms (Diphyllobothrium sp.)

Tapeworms are a white segmented (band shaped) worm that live in the digestive tract of fish. They can rob fish of nourishment from the food they eat, and make the fish’s abdomen look full when it is really full of tapeworms. Typically the hobbyist will not know the fish has tapeworms until the fish begin to pass some segments. Tapeworms can be several inches long, flat and segmented.

California blackworms (Lumbriculus variegatus) are a common source of introducing tapeworms to the aquarium system. Discus are the most common fish in the hobby to be a host to tapeworms.


PraziPro is very effective against tapeworms, and skin and gill flukes.

Luckily, tapeworms are easily treated with praziquantel (PraziPro). Tapeworm are very sensitive to praziquantel, and it is not unusual for fish to start passing tapeworms within 30 minutes of being exposed to the medication. Discus hobbyist can be surprised by how many of their fish are carrying tapeworms when the aquarium is treated with praziquantel.


Capillaria are a common parasite that is found in the digestive track of many species of fish. The worms can be transmitted to fish by feeding live tubifex and California blackworms. Fish can also contract the parasite by ingesting Capillaria eggs excreted by infected fish housed in the same aquarium.

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