Ever seen this parasite on a fish? Often found on Koi and other pond fish, the adults are large (from several mm to 30 mm), clearly visible to the naked eye and flattened on both sides. The genus Argulus contains about 130 species that are found in both fresh water and marine habitats. The parasite attaches to the body of fish with a pair of suckers located on the abdominal side(belly) of the crustacean. This parasite easily moves in the water column in search of a victim.
Argulus sp. is considered to be one of the more dangerous parasites of fish. At the larvae stage, Argulus sp. feeds on the mucous membranes and skin cells of fish. At an older age, it pierces the skin of the host with a special “needle” (stylet) and sucks blood and body fluids. At the puncture site, local inflammations and hemorrhages are formed. Digestive enzymes are produced in the glands of Argulus sp., these are injected into the wound through the proboscis, adding secondary damage to the area. During the stinging, dangerous bacteria and protozoa can be transmitted directly into the wound and bloodstream, for example, Aeromonas sp. bacteria and Tripanosoma sp. blood parasites. Argulids are crustaceans (distant relatives of shrimp and crabs), but they belong to the group of Branchiura and form the Arguilidae family.
If you see this crustacean on the body of a fish, you can remove it with tweezers. You can also treat the aquarium with eSHa alx, which will target the adults and larvae, which hatch from eggs.
Caution though, these treatments generally also kill shrimp and crabs.