Causative agent: Argulus spp. — parasitic branchiuran crustacean (disc-shaped)
Fish lice (Argulus spp.) are among the most easily spotted external parasites in Australian freshwater aquariums and ponds. Unlike the microscopic parasites that cause diseases such as Ich, Argulus are large enough to see with the naked eye — flat, semi-transparent, disc-shaped crustaceans up to five millimetres across that attach to the fish's skin and feed on blood and mucus. Infested fish typically display restless, frantic swimming behaviour, scraping themselves against tank decorations in an attempt to dislodge the parasites. In Australian backyard ponds, fish lice are a common summer pest, particularly among goldfish and koi. Treatment involves physically removing visible lice with tweezers, followed by a course of Aristopet Paracide or Aquasonic Para-Gone to kill larvae and eggs in the water. Because Argulus lay their eggs on surfaces within the tank rather than on the fish, a thorough scrub and disinfection of the aquarium is recommended as part of treatment.
Symptoms
- •Visible flat, disc-shaped parasites (up to 5 mm) on skin and fins
- •scratching/flashing
- •redness or inflammation at attachment points
- •clamped fins
- •restlessness
- •secondary bacterial infections
Treatment
- •Manually remove with tweezers
- •Dimilin (diflubenzuron)
- •potassium permanganate bath
- •salt baths
- •organophosphate treatments (where licensed)
- •treat tank for eggs
Australian Medications
- •Aristopet Paracide
- •Aquasonic Para-Gone
- •potassium permanganate
Commonly Affected Fish
- •Goldfish, koi, and pond fish most commonly affected
- •can affect most freshwater and some marine fish
Important Notes
More common in pond fish and new imports. Eggs are laid on tank surfaces — scrub and disinfect tank as part of treatment.