Ornamental fish are often raised on fish farms where they receive limited treatment for parasitic diseases. Some aquarium fish are also still collected from the wild, where they may have naturally occurring parasites. The fish often arrive to the fish retailer with external parasites and should be treated with appropriate medications to reduce parasites before being sold to customers. Appropriate diagnostic tests need to be conducted to determine which parasites are present; often more than one type can be found on the fish. Each type of parasite needs a different medication to treat it effectively.
The most common metazoan parasites of fishes include Monogenean trematodes: Dactylogyrus (gill flukes) , Gyrodactylus (skin flukes) , Cleidodiscus , Diplozoon ; Digenean trematodes: Sanguinicola , Clinostomum , Neascus ; Cestodes (tapeworms): Bothriocephalus , Caryophyllaeus, Diphyllobothrium. Ligula; Nematodes (roundworms): Anisakis, Capillaria , Camallanus ; Annelids (segmented worms): Piscicola (leeches ); Crustacea: Lernaea (anchor worms ), Ergasilus (gill maggots), Argulus (fish lice)
Treating the fish involves using medicated dips or by adding medication into the aquarium water. Some medications can also be supplied in the food. Medicated food containing fenbendazole can be used for treatment of intestinal nematode parasite infestations and should be fed for a minimum of 3 consecutive days. Repeated treatments may be necessary to effectively treat some parasites.
External monogenean flukes are best treated using Praziquantel, usually dissolved into a solution of formalin or alcohol. Praziquantel kills monogenean parasites on gills, skin, and fins. Hydrogen peroxide and peracetic acid combination (Minn Finn) has shown some effectiveness in reducing flukes. Crustacean parasites have historically been treated with organophosphates such as Trichlorfon, but safer treatment such as diflubenzuron and lufenuron are commonly used now. The fish should be checked after treatment to ensure that the parasites have been completely cleared. Retreat as necessary prior to selling fish from the stores.
Preventing occurrence of some parasites, such as digenean flukes, involves removal of the intermediate hosts, such as snails or crustacea, and keeping birds and other wildlife out of the farm ponds.
Key Words: Parasites, monogenean trematodes, crustacea, ornamental fish