Anchor Worm
Lernaea
Moderate severity ⚠️ Contagious
A visible crustacean parasite that embeds in the skin, leaving a thread-like tail.
Symptoms
Early recognition is the key to a good outcome, so inspect your fish daily at feeding time. Whitish-green threads hanging from the body, red inflamed attachment points, rubbing and flashing. If you notice several of these signs together, act promptly rather than waiting.
Causes
A parasitic copepod usually introduced with new fish or pond plants and live food. In almost all cases the underlying trigger is stress, poor water quality or the introduction of an infected fish, all of which weaken a fish's natural defences.
Treatment
Remove visible worms with tweezers and dab the wound with antiseptic, then treat the tank with an anti-parasitic (diflubenzuron) to kill larvae over several weeks.
Throughout treatment, increase aeration, remove activated carbon from the filter (it absorbs medication), complete the full course even after symptoms fade, and keep the water immaculate with regular changes. Always follow the medication's dosing instructions and dose for the tank's true water volume.
Prevention
Quarantine new fish and pond plants; inspect arrivals carefully. The golden rules are simple: quarantine every new fish for 2-4 weeks, never overstock or overfeed, avoid sudden temperature or chemistry swings, and perform regular partial water changes. A stable, clean, low-stress aquarium prevents the overwhelming majority of disease outbreaks.
FAQ
Can I just pull anchor worms off?
Where do anchor worms come from?
How serious is Anchor Worm?
Can Anchor Worm be prevented?
Will my other fish catch Anchor Worm?
This information is general guidance, not veterinary advice. Consult an aquatic vet for serious cases.