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Fish diseases can be notoriously hard to diagnose, but one of the more easily recognizable illnesses is an internal parasite called the camallanus red worm. There are multiple species of nematodes or roundworms that are part of the Camallanus genus that can infect aquarium fish. They feed by attaching to the intestinal walls and can often co-exist with their host for a long time. However, added stress factors like bad water quality or tank aggression may weaken the immune system, allowing the worms to cause serious damage and even mortality.

Does My Fish Have Red Worms?

In the early stages of the disease, the fish looks quite normal for a while. Then you may start to notice that juvenile fish are growing more slowly than usual, the adults may not be breeding as much, and you are gradually losing a few fish here and there over the course of months. Some hobbyists also reported a loss in appetite.

The telltale sign of this sickness is when you see one or more small, red worms coming out of the fish’s anal vent. It can look like a cluster of little, scarlet threads sticking out about ¼ to ½ inch (0.6–1.3 cm). At this point, the disease is at a very advanced stage where the fish may look abnormally thin (from the worms absorbing all the nutrients) or have a belly swollen with worms. Because the worms are blocking the intestines, secondary infections can take root and cause other symptoms to appear.

Camallanus red worms are often more noticeable in small livebearers like guppies because it only takes a few worms to cause serious problems in a nano fish. The worms need a much longer time to multiply to a point where the population that is large enough to take down bigger fish like angelfish.

Guppy with camallanus worm protruding from the anal vent

What Causes Camallanus Red Worms?

If infected fish are introduced to your aquarium, the sick fish passes out the worm larvae in its waste, which are eaten by tiny crustaceans like cyclops. When a healthy fish eats the infected crustaceans, it becomes contaminated and the larvae mature in the fish’s body into adults that can reproduce, thus continuing the cycle. Some species of camallanus worms do not need an intermediate host, and fish can get infected directly by nibbling on fish feces that contain larvae. Either way, the disease is fairly contagious, so adding plants, gravel, or equipment from an infected tank to a healthy tank can cause cross contamination that also spreads the parasite.

How Do I Get Rid of Camallanus Worms?

Treat the fish with a dewormer like Fritz Expel-P that contains levamisole and targets roundworms like camallanus. The medication works by paralyzing the adult worms so they can be expelled from the fish and removed via an aquarium siphon. Follow the manufacturer’s instructions on the box by using 1 packet of Expel-P per 10 gallons (38 L) of water. After 24 hours, perform a 25% water change to remove the excreted parasites. Since levamisole does not affect unhatched eggs, wait two weeks after the initial treatment and then dose the tank again with Expel-P to deal with any remaining worms.

Fritz Expel-P medication for parasitic diseases

Some articles recommend putting the dewormer in food and feeding it to the fish, but we like to treat the water of the whole tank because sometimes fish lose their appetites and you cannot always control how much medication each fish eats. Also, if your fish has secondary infections that need to be addressed, consider using broad-spectrum antibiotics or antifungal treatments as needed.

Besides medication, the key to recovery is lowering stress in the aquarium or hospital tank. Feed plenty of high-quality foods to help them gain weight and expel the worms more quickly. Keep the water quality high and vacuum the substrate more frequently to remove any paralyzed parasites. Also, consider disinfecting any nets, siphons, and other shared equipment to stop the spread of disease.

Dosing a packet of Expel-P

How Do I Prevent Camallanus Worms?

We recommend quarantining all new fish for a few weeks to observe their behavior, appetite, and overall health before adding them to your display tanks and potentially infecting your existing animals. Preventative treatment with the quarantine medication trio helps ward off most bacterial, fungal, and parasitic infections, but if you are worried specifically about camallanus worms, consider adding Expel-P as a separate treatment regimen afterwards. Most fish can survive with red worms for a while before it becomes problematic, so keep clean water, feed fresh foods, and endeavor to lower the stress in the tank. Finally, avoid cross contamination by keeping the quarantine tank in a separate area, washing your hands thoroughly after touching the quarantine tank, and using separate nets and siphons for fish in quarantine.

For more information on fish diseases, check out our collection of articles to learn how to identify, diagnose, and treat the most common illnesses.

Attributions
190729 Guppy 01 by BlueBreezeWiki (CC BY-SA 3.0)