Worms

Diagnosing worm infestation is not always a simple task for most fishkeepers and is at best, just guesswork. When a fish is eating well yet is still not putting on weight, intestinal worm infestation may be suspected. Particularly when a fish eats regularly yet actually looses weight. This is usually seen as thinning along the back on either side of the dorsal fin. In an extreme case, this may result in a well-fed fish actually starving to death.

Most worms found in aquarium fishes live in the intestine and can readily be removed with various drug treatments. However, others have larval stages that live in lymph ducts and blood vessels, and they can be difficult to treat. Most worms do not pose a serious health risk for rainbowfishes because they often have complicated life cycles in which the fish may serve as only one of possibly several intermediate hosts. Since the necessary intermediate hosts are not usually found in an aquarium, transmission of the worms to the fish does not readily occur. Therefore, worms are more likely to appear in wild-caught specimens or in rainbowfishes that are bred or maintained in outdoor ponds.

However, Camallanus is one such species that can be found in aquarium fishes and can cause considerable damage to the host fish. Several species of Camallanus have been reported from freshwater aquarium species around the world. The most common species are Camallanus cotti and Camallanus lacustris, both of which produce live larvae. Female specimens can attain a length of up to 10 mm, while males usually only grow about 3 mm long. They are commonly found infecting rainbowfishes maintained in outdoor ponds. Even if successfully treated, most rainbowfishes do not recover fully and often die from other complications.

Camallanus are ovoviviparous with mature females releasing motile infective larvae. Juvenile worms are vented with the fish's faeces and ingested by other fish. This can result in heavy infestations in some situations. Camallanus infection will initially be noticed as red-coloured worms protruding from the anus of the fish, most noticeable after feeding. Other clinical signs include wasting (anorexia), abdominal swelling, and extensive lesions in the rectum mucosa. The worms attach to the wall of the fish’s intestines with their tiny jaws and suck its blood. This can cause considerably damage to the intestinal lining, and a reduced capacity of the fish’s ability to readily absorb nutrients.

Most Camallanus species reproduce by means of an intermediate host, which can be small crustaceans such as copepods or various insect larvae. However, the species’ relatively frequent and persistent occurrence in aquaria worldwide strongly indicates flexibility in its life cycle, i.e. the ability to infect the final host directly.

Research has shown that under aquarium conditions, without any presence of an intermediate host, Camallanus cotti is able to infect various fish species directly for at least three generations. It was further shown that the infective free-living first-stage larvae may survive for more than three weeks in the aquarium environment and that their host-attracting behaviour is not precluding direct transmission to the final fish host. Therefore, any treatment for Camallanus worms should be directed towards both individual infected fish hosts as well as the free-living larvae on the substrate.

Treatment There are numerous recommended chemical treatments for internal worms. Among them are Piperazine, Levamisole, Fenbendazole, and some specific aquarium medications. However, mixed results have been reported using these drug treatments and it is sometimes difficult to remove Camallanus spp. from infected aquaria. Some success has been reported using the following treatment regimes:

Fenbendazole has been used to control intestinal worms in fish. A dosage of 25 mg/kg, delivered in food for 3-5 days, has been commonly recommended, but this regimen has not been evaluated in controlled trials. Flubendazole 5% mixed with fish food at 100 mg/100 gm of food. Feed every second day for 5 days. On those days feed only once with the regular diet. Treatment should be repeated after 21 days. It is suggested to enhance the food with codliver oil and bind it with gelatine or agar, since fish are quick to refuse food, which has been medicated. Withholding food for a few days prior to feeding medicated food may aid in acceptance. As a bath, it can be used at 2 mg/L of water once a week for three weeks.

Mebendazole is chemically related to flubendazole and fenbendazole. It is a benzimidazole derivative, and is a useful broad spectrum anthelmintic; the drug of choice for mixed worm infestations. Some sources suggested that water soluble ivermectin might overtake mebendazole as the drug of choice for mixed worm infestations.

Ivermectin 1% - Some studies have shown that ivermectin added directly to aquarium water has been useful in treating Camallanus spp. in fish. The dose used was 0.7 millilitres of a 1% injectable solution per 76 litres of water. The dose was added over a period of four days (0.1, 0.2, 0.2, and 0.2 millilitres). A solution of 1 part ivermectin 1% in 19 parts distilled water can be made and administered as a split dose of 2 ml on day one, 3 ml on day two, and 3 ml on day three followed by a water change on day four. However, because this drug has a narrow margin of safety, some veterinarians advise against any use of ivermectin for aquarium fishes.

Concurat L (10% Levamisole) mixed with food at 1 gm/100 gm of food. Feed once daily over 5 days. If the fish are already weakened and refuse to eat then you can try 30 mg/L of water dissolved in a little water beforehand. After 3 days do a 50% water change and dose again. After another 3 days repeat the waterchange. Levamisole is a widely used drug to treat nematode infections in fish and has been reported to kill both the infective free-living larvae and the fish parasitic stages of Camallanus cotti.

Praziquantel at 2-10 mg/L for 1 to 3 hours in a bath is effective in treating adult worm infections in fish. Praziquantel has been identified as the most effective “in water” treatment of infected fish. Praziquantel can also be administered in food at 35-125 mg/kg for up to 3 days. Praziquantel was traditionally available in the form of branded Droncit® tablets, for oral administration in dogs and cats, but is now available in a range of aquarium products. Praziquantel is usually harmless to fish of all species, is non toxic to plants, and has no negative impact on nitrifying bacteria. However, there are reports that Kissing Gouramis (Helostoma temminckii) have been adversely affected by Praziquantel (98.5%).