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Parasites in Fish ? Bendazole (Fenbendazole) ? Panacur

Parasites in Fish

Most of the drugs listed below are anthelmintic (antihelminthic) drugs. These are chemical preparations that effectively destroy various parasitic helminths (“worms”). With regard to fish parasites, this group includes trematodes, nematodes and cestodes (tapeworms). These medicines are given to the fish by mouth with food, although some are also effective in the form of baths. Anthelmintics used for bath treatments have been shown to be effective against non-helminth ectoparasites such as Argulus or Argulus carp lice. If the dosage for a specific drug is not listed, you should consult your veterinarian.

Many of the anthelmintic drugs used to treat fish are also used in humans, so in some countries they can only be obtained through a veterinarian. Other such agents, for example trichlorfon, are organophosphorus compounds. These are extremely toxic chemicals, and their sale is highly regulated.

It is important to remember that the life cycle of ectoparasites is quite complex and includes many stages. Some stages are resistant to chemicals, others are more vulnerable. Since resistant stages can remain viable for a long time, re-treatment is often necessary to completely eradicate the parasites.

In addition to the chemicals listed below, there are a number of specialty aquarium medicines on the market for some of the larger ectoparasites. They should be used in accordance with the manufacturer’s instructions. It is very important to follow through with the recommended course of treatment. Allow enough time for the eggs or cysts that are resistant to chemicals to hatch into larvae.

Bendazole Fenbendazole (Panacur)


Fenbendazole is used primarily to treat worms in horses. In addition, it is useful in the fight against fish nematodes such as Camallanus. It can be purchased as an equine anthelmintic. In the aquarium hobby, this medicine is used as a powder or granule, not a dough. A three-week course of treatment is carried out by the method of long baths with a dose of 2 – 3 mg/liter, and on the 7th and 14th days, the procedure is repeated.

Fenbendazole (PANACUR) aquarium dosage

Also be aware that fenbendazole seems to soak into the porous live rock and be absorbed indefinitely. I know one hobbyist who transferred a small piece of live rock that had been treated with fenbendazole (Panacur) months earlier into a reef tank, where it killed the resident starfish and Astrea snails. So enough of the medication may be retained within treated live rock to impact sensitive animals months after the fenbendazole was administered. Don’t treat live rock intended for reef systems with fenbendazole (Panacur)!

At the lower dosage recommended for nursery tanks (1/16 tsp. Per 10 gallons), fenbendazole normally does not harm cleaner shrimp and decorative shrimp. With the exception of Astrids (Astrea), Coit and Worden have found it does not usually affect the types of snails typically used as cleanup crews (e.g., Nassarius, Ceriths, and Nerites). It will kill starfish but copepods, hermit crabs, and shrimp are normally not affected.

Macroalgae such as the feathery or long-bladed varieties of Caulerpa or Hawaiian Ogo (Gracilaria) are not harmed by exposure to fenbendazole at even triple the normal dose. In fact, if you will be using Caulerpa in your nursery tanks to provide hitching posts for the fry and serve as a form of natural filtration, it’s a very wise precaution indeed to treat them with a regimen of fenbendazole beforehand.

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So fenbendazole (FBZ) or Panacur is primarily useful for ridding bare-bottomed nursery tanks and dwarf seahorses setups of hydroids and Aiptasia anemones, ridding Caulerpa and other macroalge of hydroids or Aiptasia before its goes into the aquarium, and cleansing live rock of bristle worms, hydroids, and Aiptasia rock anemones before it is introduced to the aquarium.  If you are serious about raising seahorse fry, fenbendazole is must-have med for keeping your nurseries hydroid free.

It can also be used to eradicate bristle worms, hydroids, an Aiptasia from an established aquarium if it does not house sensitive animals such as live corals and gorgonians, starfish, Astrea snails, or tubeworms and other desirable worms that may be harmed by FBZ, providing you monitor the ammonia levels closely and are prepared to deal with the ammonia spike that may result from the sudden death of the worm population.

Caution: For aquarium and ornamental fish only. not for human use. keep out of the reach of children. keep the container tightly closed and in a cool dry place. not to be given to fish intended for food use.