Fish Lice (Argulus japonicus) in Goldfish (Carassius auratus).

Fish lice (Argulus spp; family Argulidae) are branchiuran crustaceans that parasitize both marine and freshwater fishes. Argulus spp can be a major threat to fish health, because heavy infestations can cause significant morbidity and mortality. In addition, fish lice are known to be the vehicle for other fish diseases. During rounds at our facility, Argulus japonicus was collected from the caudal and anal fins of 3 goldfish (Carassius auratus). These goldfish were asymptomatic, and no additional cases were noted after manual removal of the lice. As soon as any Argulus organisms are identified, management and treatment are recommended because infections can escalate rapidly. Currently, there are no FDA-approved drugs for the control and treatment of this parasite, but several chemicals including organophosphates and diflubenzuron have been used with success. The screening and quarantine of incoming fish is the best way to avoid a facility-wide Argulus infestation.