Causative agent: Lernaea spp. — parasitic copepod crustacean (anchor-shaped)
Anchor worm (Lernaea spp.) is one of the most visually unmistakable parasites encountered in Australian freshwater fishkeeping — the thread-like worms, up to two centimetres long, can be seen protruding from the fish's body, often with an angry inflamed crater where the parasite has burrowed its anchor-shaped head into the muscle tissue. Despite the alarming appearance, anchor worm is treatable when caught early. The worms must be physically removed with fine tweezers, and the wound disinfected with diluted potassium permanganate or antiseptic. The entire aquarium must then be treated to kill eggs and larvae before they develop into new parasites — Aristopet Paracide and Aquasonic Para-Gone are widely available in Australian pet stores for this purpose. Multiple treatment rounds are typically required. Anchor worm is particularly common in goldfish and koi purchased from outdoor pond displays, and any new pond-kept fish should be closely inspected and quarantined before joining an existing community.
Symptoms
- •Visible worm-like threads (1–2 cm) protruding from the skin
- •inflamed, red, or ulcerated attachment site
- •fish scratching against objects
- •lethargy
- •secondary infections at wound
Treatment
- •Manually remove with fine tweezers (dip wound in diluted potassium permanganate)
- •potassium permanganate bath
- •Dimilin (diflubenzuron)
- •treat tank to kill larvae
Australian Medications
- •Aristopet Paracide
- •Aquasonic Para-Gone
- •potassium permanganate via aquarium suppliers
Commonly Affected Fish
- •Goldfish, koi, and most freshwater ornamental fish
- •very common in fish from outdoor ponds and new imports
Important Notes
Always treat the whole tank after manual removal to kill eggs and larvae. Multiple treatment rounds are needed. Common in new goldfish imports.