“The camallanus worm is a type of nematode worm that can inhabit the intestines of tropical and semi-tropical fish. This worm is quickly identified by the red paintbrush like worm tails that may protrude from the affected fish’s anus.” (PetFish.Net, 2006)

What causes the disease?

There are numerous species of Camallanus worms, and while some parasitize only a limited range of fish species, others can be found in many different hosts. (Monks, 2015)

The species most often implicated in infections of aquarium fish is the East Asian species Camallanus cotti. A second species, Camallanus lacustris from Europe and West Asia, is sometimes implicated as well. (Monks, 2015)

Mature worms are red because they feed on blood. In addition their activities irritate the digestive tract and adjacent organ systems, potentially causing internal bleeding and secondary bacterial infections. (Monks, 2015)

What is its life cycle?

The life cycle of Camallanus worms passes through three key phases, a free-living stage, a series of moults during which time the worms infect an intermediate host (a crustacean) and then another moult that takes place in the final host (the fish). (Monks, 2015)

After mating, mature females begin the cycle by producing large numbers of first-stage larvae. When the fish defecates these will be carried out into the environment. These larvae quickly settle out onto the substrate where they wiggle about, tricking small crustaceans into eating them. Once that happens the larvae move into the host’s gut where they feed and grow. (Monks, 2015)

Within about a week they will have moulted twice to form inactive third-stage larvae that sit inside the host. Should the crustacean be eaten by a fish, the third-stage larvae become active and start feeding again, eventually moulting twice to form the sexually mature male or female adult worms. These are the distinctive red worms aquarists see protruding from the vents of infected aquarium fish. (Monks, 2015)

How is it transmitted?

Possible pathways include cannibalism and ingestion of faeces produced by infected fish. (Monks, 2015)

What are the symptoms?

Light infections of Camallanus worms are difficult to detect. Serious infections can be indicated by the presence of red, thread-like worms emerging from the anus of the aquarium fish. Mature Camallanus worms are a couple of millimetres long. (Monks, 2015)

Other symptoms of Camallanus worms in aquarium fish include abdominal bloating, wasting, and disinterest in food. Negative environmental pressures such as overcrowding, poor diet, and poor water quality will reduce the immune response of infected aquarium fish, making it easier for the worms to multiply and cause damage to their host fish. (Monks, 2015)

What treatment is available?

There are numerous medication options for treating Camallanus worms in aquarium fish including fenbendazole, levamisole, and praziquantel. These do not necessarily kill the worms, and in some cases only paralyze them, which results in them being pushed out of the gut and into the aquarium. Within 24 hours of medicating the substrate should be thoroughly cleaned to remove the worms. Normally three treatments are required, each one week apart. (Monks, 2015)

Antihelminthic medications may be toxic to fish if used other than as described by the manufacturer, and when treating expensive or delicate fish veterinarian advice is highly recommended. (Monks, 2015)