The translation of this article has not yet begun. There are still open tasks such as converting units or creating tables.

10.12.2. Capillaria

Photo of author

Author : David Bogert

Published :

Time To Read :
6 minutes
Difficulty : Level 7

Excerpt :

The tropical fish disease called capillaria explained.
A common nematode worm infecting tropical fish is Capillaria worms. These nematodes produce the same symptoms as Camallanus, but they don’t protrude out the anus of the fish. It is often found in necropsies of cichlids which have shown such symptoms as bloat, white poop and not eating. It thus imitates hexamita. Capillaria can also cause hollow belly, arched back, wasting, spitting out food and intestines popping out

Capillaria may well be more common than camallanus. But capillaria is rarely diagnosed in fish, even though it is common. Capillaria can be suspected if one is getting a lot of unexplained deaths. Capillaria tend to hit livebearers especially hard for some unexplained reason. If only the livebearers in a tank are dying, suspect capillaria. Guppies seem to be especially hard hit.

Capillaria are unlike camallanus in that they produce eggs, not live larvae. The best way to diagnose capillaria is to look at the feces of the fish with a microscope. If there are barrel shaped eggs in the feces they have capillaria. It is only considered a virulent and potentially deadly problem when there are a lot of eggs in the feces. This is what the eggs look like:

Egg of a capillaria worm
Egg of a capillaria worm

These eggs are found in small quantities in most fish in the tropical fish trade. It is a subacute pathogen until something triggers it to become virulent. Oftentimes slightly cloudy or “dull” water is found when fish start dying from capillaria. Deaths from capillaria rarely found in crystal clear, bacteria free water.

A microscope is a good investment for many fish keepers. DO NOT BUY an electronic USB digital microscopes which attach to one’s computer. These microscopes don’t come in close enough nor give the magnification necessary to really see things like capillaria eggs. Instead buy a cheap student microscope. These give the 600 power one needs to see tiny eggs.


Capillaria is treated exactly the same way as camallanus. Fenbendazole (Thomas Labs Fish Bendazole, Panacur and Safeguard for dogs, and several livestock dewormers) is the most effective medication. It is the medication of choice for capillaria by public aquariums (Hadfield, 2011). Levamisole is also an effective medication if mixed into the food. Fritz Expel-P is levamisole. Levamisole can also be purchased at Amazon, subaquaria .com and Valleyvet .com. Some eBay sellers supposedly sell bogus products, look for cattle products such as Agrilabs Prohibit Soluble Drench Powder and DURVET Levamed Soluble Drench Powder Dewormer.

Other medications supposedly effective against roundworms are Pyrantel Pamoate, Flubendazole (Kusuri Wormer Plus), Ivermectin and Piperazine. In some countries this is all that are available to aquarium hobbyists.

Type of wormExamples of
this Phylum
FlatwormsFlukesPraziquantel in
Water & Food
Fenbendazole in
Water & Food
only in Food
only in Food
only in Food
only in Food
Praziquantel does not kill snails or shrimp
Fenbendazole and Levamisole kill snails but not shrimp
Treatments for Worms

All are mixed into the food at roughly a 1 to 5% level (an amount equal to a barley grain in two tablespoons). Note that the cautions about deaths of snails, shrimp and invertebrates is very dose dependent. Fenbendazole are often used with no snail deaths because the dosage isn’t high enough. Conversely using a very high dosage of fenbendazole can possibly kill shrimp. And Levamisole is safe for everything except nematodes. Praziquantel is safe with everything except planaria and flukes.

Medications do not kill the worms, they only paralyze the barbed jaws that the roundworms hold onto the gut with. So, the detached but live worms get pushed out of the gut and into the aquarium (which the aquarist will see when the pink or red worms emerge and detach from the anus). Within 24 hours of medicating the substrate should be thoroughly cleaned to remove the worms.

It is best to move the fish to a hospital tank with a bare bottom to allow the worms to be easily vacuumed up.

The life cycle of capillaria is relatively long. The eggs and larvae can exist outside a fish for months and the worms take three to four weeks to mature once inside the fish. Feed fish with Fenbendazole in the food once a month for three months in order to eliminate capillaria.

Fenbendazole, levamisole, Pyrantel Pamoate, flubendazole, Ivermectin and piperazine are FDA approved for use in humans, so they are very safe and effective in the food at the 1% to 10% level.

It is easy to make medicated food. Heat 1/4 cup water (two ounces or 58 milliliters, not a lot) in the microwave. Then blend one 1/4 ounce of plain animal derived gelatin (Knox gelatin, one envelope) into the hot water with vigorous stirring. Take two tablespoons of dry commercial fish food (pellets or flake) and mix it with just a little of the hot water/ gelatin mixture. Add hot water/gelatin until you get a paste like consistency. If it gets too watery just add more food.

Then add roughly 1/16 teaspoon (a 1% to 2% addition) of the medication to the mud. Mix and mash the whole mass thoroughly.  Spread it out into a pancake about 1/8th inch (3 mm) thick on a plastic film or a plate. Then put in the refrigerator. If you plan on keeping it for more than two weeks put it in a small plastic bag and freeze.

Feed it to your fish once every two weeks for at least one month (I do three months). Note while the fish won’t eat it like they normally do, they typically will eat some if you just leave it in the tank.  Note this gel food is 80% water. So it will require ten eyeballs per day of food per fish (six fish = 60 fish eyeballs = six times ten).

Capillaria White Poop
Capillaria White Poop

Note that API General Cure and Praziquantel do not work against capillaria. The flukes and tapeworms that praziquantel works against are completely different animals than capillaria and are not affected by praziquantel.

Some authors have vehemently advocated that Fenbendazole, Levamisole and other dewormers work great when added to the water. They say that dewormers are absorbed through the skin and the gills. This is simply not true. The dewormer molecules are far too large to be absorbed through either the skin or the gills. It just is impossible.

Internal fish diseases such as capillaria can ONLY be treated with dewormers in the food. Adding medications to the water is useless and just a waste of money. Many believe (and the instructions on the dewormers say!) that fish medications need to be added to the water. They are simply incorrect (but adding huge amounts of medication to the water makes huge profits for the suppliers!). This controversial topic is covered in the following link:

12.5. Fish Don’t Drink