Anchor Worm: symptoms, treatment, prevention

Lernaea cyprinacea is a parasitic copepod whose adult female embeds head-first into fish flesh, leaving a Y-shaped body protruding from the wound.

Overview

Anchor Worm is caused by the copepod Lernaea cyprinacea. The adult female burrows her cephalothorax into the host muscle, leaving the segmented body and egg sacs hanging outside. The disease mostly affects pond fish but enters home aquaria through new fish or plants from outdoor sources.

Symptoms

Worm-like protrusion from the skin
Ulcers around the attachment point
Scratching against decor
Secondary bacterial infection
Weight loss
Lethargy

Causes

Introduction with new pond fish (especially koi and goldfish), with plants from outdoor sources, or with infected food. Free-swimming larvae infect new hosts in warm weather.

Diagnosis

A whitish-greenish thread-like worm with paired egg sacs protruding from skin is pathognomonic. Look around fin bases and gill covers; in heavy infestations multiple parasites may be present.

Treatment

Manual removal of adult worms combined with a chitin-synthesis inhibitor cycle in the tank eliminates the parasite. Always treat the wound to prevent secondary infection.

Quarantine

Move affected fish briefly into a holding container to remove worms. Treat the original tank with a chitin-inhibitor because larvae and eggs remain after the adults are gone.

Medication

Net the fish, grasp each adult worm with forceps and remove it cleanly, then treat the wound with a fish-safe antiseptic.
Diflubenzuron at 0.01 mg/L in the tank, once weekly for 4 weeks, to kill juvenile copepods as eggs hatch; harmful to crustacean invertebrates.
Potassium permanganate bath at 10 mg/L for 30 minutes for severe infestations; harsh on fish but kills attached parasites and free larvae.

Recovery

Watch wounds for ulceration and treat secondary bacterial infection promptly. Continue water changes throughout the chitin-inhibitor course.

Prevention

Quarantine new pond fish
Rinse plants from outdoor sources
Inspect new fish carefully for visible parasites
Diflubenzuron prophylaxis for koi imports