Crustacea

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Lernea (Anchor Worm), Argulus (Fish Lice), Ergasilus


Argulus (fish louse)

Argulus (Fish Lice) and Lernea (Anchor Worms) are large external parasites, visible with the naked eye.

Fish Lice (Argulus) are a flat worm with a somewhat round body. They usually only affect pond fish. They have eight legs and use two large hooks to attach to the fish body. It is about 1/8 th of an inch long and have characteristic dark eye spots. They suck blood, so when they are removed through treatment, a wound treatment should be used, such as Melafix. Yhese wound often lead to secondary microbial infections.



Lernea (Anchor Worm)

Lernea (Anchor Worm) is a crustacean. They are quite long and visible to the naked eye. They are up to 0.8 inches (20mm) long. Only the female attaches to the body. She is held in place by an anchor. They attach to the muscle of the fish and feed. Two egg sacs develop as a forked extension at the end of her body.



Ergasilus

This is a fairly common crustacean on the gills of freshwater fish. It is characteristically blue in color, and is an average of 1.5 mm in length and 0.5 mm in width. Ergasilus attacks the vascular system and gills. Ergasilus is sometimes called "gill rot."

Symptoms and Behavioral Signs
Fish infected by external parasites exhibit abnormal swimming patterns-- jumping up and down, rubbing their bodies against the sides and bottom of the tank. The parasites are often big enough to be observed with the naked eye, or at least with a magnifying glass. Thread-like tentacles hanging from the gills are an indication of ergasilus.

Causative Condition
Crustacea may enter tanks via plants or live foods, or from new fish introduced to the fish room.

Prevention and Treatment
Masoten has been used to control Argulus spp., Ergasilus spp., Lernaea spp. Other products used to treat the crustacea include Dimilin [diflubenzuron] and Larvadex.
Lufenuron, commonly available as a tablet to control fleas in dogs (Novartis Program) is currently the drug of choice because it is safer. See the article on lufenuron.

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