Argulus foliaceus, also known as the common fish louse or the carp louse, is actually not a louse or even an insect at all, but a crustacean. Within the class Maxillopoda, the subclass Branchiura consists of about 150 species of freshwater and marine fish ectoparasites. The genus Argulus is found throughout the world. Argulus foliaceus is native to Europe, but is also common on aquarium and pond fish worldwide. Although the louse shows some host preference, especially for carp, it is usually considered a generalist and is found on a variety of fish species. The oval-shaped, flat adults attach to fish hosts using hooked suckers. They inject digestive enzymes into the host and feed on blood and tissue fluids. Symptoms of lice infestation include abnormal swimming, rubbing, and deteriorating physical condition. Because of tissue damage caused by the parasite, secondary bacterial and fungal infections frequently occur. Adult females leave their hosts and lay eggs on vegetation or other submerged objects. Adults can live free of hosts for two to three weeks, but newly hatched larvae only survive a couple of days if they do not find a host. Treating an infested aquarium may require several approaches, so prevention is best. Always visually inspect and quarantine new fish. Lice may be removed from fish manually with forceps. Fish should be transferred to an alternate aquarium while chemical treatments are used to kill remaining adults, larvae, and eggs.
Contributed by Elizabeth McCarthy, Bucknell University.
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