How to Get Rid of Nematodes in an Aquarium?

Nematodes can cause a lot of damage inside an aquarium. These little worms amass in the hundreds inside the aquarium, eating the fish inside out.

These ‘white worms’ typically appear when the oxygen content is low due to warm water.

Getting rid of nematodes from the aquarium is essential.

Fish that eat nematodes can die as the worms infest the guts and intestines of the fish.

Here you learn all there it is to know about the two common types of nematodes that invade the fish tank – Camallanus and Cappilaria.


Camallanus are nematodes that infest aquariums with low oxygen levels.

They are the same cylindrical roundworms that cause diseases in animals. These worms are shorter and have a segmented appearance similar to tapeworms.

Camallanus is a genus of parasitic roundworms. There are different species of the camallanus worm.

They are mostly found in the form of live larvae. The females incubate eggs in their bodies and produce the larvae.

These larvae find their way inside the fish when they ingest the water.

The nematode affects mostly freshwater fishes such as cichlids and live-bearing fish. Some people wrongly assume that fish get infected with camallanus worms due to consuming bloodworms.

The fact is that bloodworms are insect larvae that don’t have any parasites. However, they may have pests like leeches, so you should not feed them to the fish.

How to Detect Camallanus Nematode?

Camallanus is easy to identify in an aquarium. You should look for reddish-brown worms extending from the anus of the fish. The worms may appear similar to small red feces.

In case of a serious infection, the fish’s anus becomes swollen, and you may see worms hanging out.

A long time camallanus infection can result in a hollow belly appearance since the intestines can’t absorb the food nutrients.

Red threadlike worms that emerge from the fish anus are females that release larvae in water. The red and threadlike appearance often makes people mistake it for feces as it extends from the anus of the fish.

The reddish-brown worms thrive in the guts and intestines of the fish. They can only be noticed once the worms start protruding from the back of the fish.


Capillaria is another type of nematode similar to camallanus worms. They produce the same symptoms but do not protrude from the anus.

The worms can be suspected to be inside the fish tank if you notice a lot of sudden deaths.

Capillaria infect almost all types of fish but the cichlids, guppies, and livebearers are the hardest hit. If you see these fishes dying in large numbers, the main suspect is capillaria.

The nematodes are more common in aquariums compared to the camallanus. Mostly, they are found in necropsies of the fish that develop symptoms of bloat, such as not eating and white feces.

Eggs of capillaria are found in small quantities in wild fish. The nematode is a subacute pathogen that becomes virulent only when triggered by environmental conditions, such as warm water and low oxygen levels.

The nematode thrives in mostly dull and cloudy water. They are rarely found in clean water in an aquarium with proper filtration systems.

How to Identify Capillaria in Aquarium?

Capillaria nematodes produce eggs instead of living larvae similar to camallanus. You can look at the feces with a microscope to confirm the infection. If capillaria has infected the fish, you will see barrel-shaped eggs in the feces.

The most well-maintained aquarium has some population of the nematode. They are common in most wild fish. Light nematode infection is not noticeable in most fish. Isolated infections are not serious or fatal for fish.

But if the water conditions are bad, the nematode can multiply in number, resulting in serious infection and mortality.

Livebearers and freshwater fish are particularly vulnerable to the nematode. An entire colony of livebearers can be wiped out by the nematode worms.

How to Get rid of Nematode from Fish Tank?

Nematode thrives in dirty water. A high bacteria count in the water reduces the immune system of the fish.

This makes it easier for nematodes to multiply inside the fish and cause serious diseases and even death.

To get rid of nematode in an aquarium, you need to make sure that the water is kept clean. Install a high-quality filter that can remove waste from the aquarium.

Moreover, you should replace dirty water at regular intervals, depending on the fish population.

Consider replacing 50 to 75 percent of the water from the aquarium once a week. You should dechlorinate tap water before adding it to the aquarium.

Nematodes thrive in warm water conditions. So you need to make sure that the water temperature is not high if using a heater.

Avoid heating the water to more than 800F to reduce the population of nematodes inside the aquarium.

Treating Nematode Infection in Fish

Camallanus and capillaria nematodes require the same treatment.

You can add dewormer to food to get rid of nematode infection in fish. Adding medication directly to the water will not prevent the infection.

Don’t go by the label that states that adding medication can remove nematode inside the aquarium.

The most effective medication for treating nematode infection is Fenbendazole. The medication is generally used for treating nematodes in public aquariums.

Another effective medication is Levamisole which you can buy in most online stores. However, some sell bogus medication, so you should read the reviews before ordering online.

Other medications that are effective in treating nematode infection include Piperazine, flubendazole, and Pyrantel Pamoate.

These are FDA-approved medications that are easily available in aquarium stores. They are selective medications that only affect nematode worms leaving snails and shrimps unharmed.

The medications don’t kill the nematode but instead paralyze the jaws around the worms that they use to hold on to the guts of the fish.

This causes the paralyzed but alive worms to be pushed out into the aquarium.

The worms will emerge from the back of the fish and will be completely removed from the fish’s gut.

You should transfer the affected fish to another tank with a bare bottom. You should vacuum the paralyzed worms and then transfer the fish again to the regular tank.

How to Give Nematode Medications to Fish?

The medications should be mixed with the food at a ratio of 1 to 5. Making the medicated food is not difficult. Heat about a quarter cup of water in a microwave for about five minutes.

Next, you should mix about a quarter ounce of medication in hot water and mix vigorously.

You should mix the heated water with two tablespoons of commercial fish food flake or pellets. Stir the mixture until it gets a paste-like consistency.

If the mixture seems watery, you should add more food to it to achieve the desired consistency.

Mix the paste thoroughly and spread it out into a pancake on a plate. Put the mixture in the refrigerator for the fish.

If you plan to give the medication to lots of fish for more than two weeks, you should put the mixture in a plastic bag to put in the freezer.

Feed the medicated food to the fish for about a month. The fish may not eat the medicated food like they eat traditional food, which is why you should leave the food in the aquarium, and they will likely eat some.

It’s important to remember that medications for getting rid of Nematodes, including camallanus and capillaria, are effective only if mixed with the food.

Adding medication to the aquarium water is not effective in getting rid of nematode infection in fish.

Some dewormer medication instructions say that it works more effectively if given to the fish directly by adding it to the water.

This is a false statement.

The medication molecules are too large, which is why it cannot be absorbed through the gills or the skin of the fish.

Treating the Aquarium to Get Rid of Nematode

After treating the fish, you should treat the tank to get rid of the nasty worms from the aquarium.

To treat the tank, you should add about 2-milligram Levamisole or other medications per liter.

So, if you have a 50-liter tank, you need to add 100 milligrams to one tank.

Leave the mixture for about 24 hours and carry out a 70 to 100 percent change of water. Make sure that you vacuum the gravel thoroughly.

This is important since the medication only paralyzes the nematodes instead of killing them. You need to suck them out using a gravel vacuum to remove them from the aquarium.

The aquarium treatment should be repeated after 2 weeks and again at 5 weeks to remove the remaining nematode in the tank.

Final Remarks

Nematode worms are the most commonly encountered pathogen in an aquarium. The worms infect a wide range of mostly freshwater fish.

Some saltwater fish eat the worms that invade the aquarium. But they are a bane for most fish species.

Make sure that the aquarium water is kept clean. The water temperature should also be kept at a required level for the fish.

Too much warm water can deplete oxygen and increase the risk of nematode infection.

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