Copepods are another group of parasitic crustaceans with a diversity of body forms with variable appendages. An example is
Lernaea species (anchor worm), which is an elongated copepod that embeds its head into the skin of fish, leaving its Y-shaped egg
sacs to hang from the fish. These sacs can easily be seen grossly. The anchor worm has a direct life cycle and lives in fresh
Organophosphates are the typical treatment for parasitic crustacean infestations. Dichlorvos and trichlorfon are the most
commonly used organophosphates for treating fish with parasitic crustacean, monogenean, or leech infestation. Trichlorfon
(0.5 to 1 mg/L) as a prolonged immersion or dichlorvos (0.5 to 2 mg/L) as a 30-to 60-minute bath is effective.1,2 Diflubenzuron (Dimilin—PondCare) is a chitin synthesis inhibitor that when used at a dose of 0.01 mg/L as a prolonged immersion
treatment can also rid fish of crustacean copepod infestation.
Figure13: Argulus species infestation on the caudal fins of a goldfish. The parasite has a flattened, saucer-shaped appearance.
Terry W. Campbell, MS, DVM, PhD
Department of Clinical Sciences
College of Veterinary Medicine and Biomedical Sciences
Colorado State University
Fort Collins, CO 80523
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