Diagnosis and Management
Because of their size, older stages of
Argulus can be diagnosed with the naked eye. The parasites are visible moving on the host or swimming in the water. The parasite can also be identified on a wet mount of the affected tissue. Captured fish should be examined quickly because
Argulus may rapidly leave the fish once it is disturbed or removed from the water. Filtering water from the system through a fine mesh net may also help capture free-swimming
Argulus adults or juveniles for identification. Adults and juvenile stages (which are similar to adults but lack suckers) are relatively easy to identify, but their identification should be verified by a fish health professional.
Drug choice and length of treatment for
Argulus infections should take into consideration the life cycle of the parasite, which varies from 30 to 60 days depending on temperature and species. Treatment should target all life stages, including eggs, juveniles, and adults, both on the fish and in the environment. Adult parasites can be manually removed from the affected fish, but this is impractical in many situations and is an incomplete solution because eggs, unattached juveniles, and adults will still be present in the environment. Fish can be moved to a clean tank and treated with the appropriate drugs, while eggs in the original system are eliminated either by cleaning and disinfecting the tank or allowing it to dry completely. However, drying may be difficult in humid areas, and at cooler temperatures eggs can survive much longer time periods. Optimal water quality should be maintained for the duration of any treatments.
Several medications have historically been used for bath treatment of
Argulus, but potential resistance to treatment, current availability, legality of use (especially in food fish species), dosage rates and associated costs, and fish species’ sensitivities may reduce options. It is best to work with a fish health specialist. There are currently no FDA-approved drugs for the treatment and control of
Argulus. Prolonged immersion of an organophosphate pesticide, such as trichlorfon (Dylox® 80, Bayer), which acts by disrupting the nervous system, has been an effective treatment when dosed at 0.25–0.50 mg/L active ingredient, once a week for 4 treatments. Unfortunately Dylox® 80, the only aquatic organophosphate 24 (c) pesticide approved for use in Florida and several other states, is no longer being manufactured. Diflubenzuron (Dimilin®, Chemtura) is another pesticide, which acts by interfering with the parasite’s molting (“shedding”) of the outer skin (“exoskeleton”) during growth and development. Diflubenzuron effectively kills both adult and larval stages, but it is a restricted-use pesticide, and applicators must follow label instructions. Other compounds with a similar mechanism of action as diflubenzuron, such as lufenuron (Program®, Novartis Animal Health) at 0.13 mg/L, have also been used with success. Potassium permanganate (10 mg/L for 30 minutes, or 1.3 mg/L applied twice over 3 days) has been shown to be effective in killing the juvenile and adult stages of freshwater species in several studies. Potassium permanganate is not recommended for use in marine systems. Increased salt concentration does not appear to be effective for the control of
Argulus in freshwater, nor does formalin.
Emamectin benzoate (SLICETM, Merck Animal Health) is an in-feed product that has been shown to experimentally control
Argulus infections in goldfish and koi. Emamectin is licensed outside the U.S. for control of sea lice, a saltwater copepod parasite; however, in the U.S. emamectin is an FDA Investigational New Animal Drug (INAD) and, therefore, is currently unavailable for general use. Those interested in its use must contact the manufacturer and enroll in an INAD study (see this site for more information:
http
/www.fws.gov/fisheries/aadap/slice.htm). Of all the drugs listed above, only potassium permanganate (in freshwater) is legal for use in fish intended for human consumption, and its effectiveness may not be ideal. There are currently no approved products for use in foodfish species. Consequently, it is critical to know where your fish are coming from and to quarantine new fish before introducing them to your system. Potentially infested fish should not be mixed with clean fish without a proper quarantine.
Effective management of an
Argulus outbreak must include proper identification of the parasite, treatment of all life stages on the fish and in the environment, and proper drug use. Drugs available for treatment of
Argulus infestations are limited, so inclusion of a fish health professional in the diagnosis and management will help minimize the biological and economic impact of an
Argulus outbreak.
