Anchor Worm Lernea fish parasite

The Anchor Worm or Lernea is not actually a worm it is a crustacean parasite and is more commonly found in freshwater fish such as Koi. It has been given the name Anchor Worm as the head penetrates the skin and develops a shape similar to an anchor beneath the surface making them difficult to remove. Two egg sacks develop at the posterior end of the body. They eat away at the soft tissue and in doing so can cause secondary infections and fungus as well as the immense tissue damage. Vital organs may aslo be damaged depending on whereabouts on the fishes body the parasite attaches.

The parasite is quite large and easy to spot with the naked eye, however it is a tough parasite and, because of the way it attaches itself, can be quite a challenge to remove and/or eliminate.
Removal is desired however as leaving them untreated will mean that they successfully reproduce and will gradually kill off the fish around them. It is only the adult female that will attach to the fish. The male dies shortly after mating.

Prevention

Any new fish should be quarantined as a matter of course before being added to an established pond. It is also a good idea not to add any water that the fish may have arrived in to the tank as young Lernea are free swimming.

The parasites will die if dehydrated. If a pond or tank is infected therefore, complete draining and leaving dry for 24 hrs will kill off any parasites. They are also salt intolerant and this will kill off the parasites also.
They cannot survive harsh winters and will die if the temperature drops below 15°C (59°F) .

Cure

Anchor Worm have to be physically removed from the fish with a pair of tweezers, the fish may need to be anaesthetised for this. It is recommended that any fish with Anchor worms attached are isolated to prevent the release of eggs into the water. Fish should also be isolated for recovery. Removal must be done very carefully as it is important to remove all of the head pieces and not just the body.

Some reports say that dipping the parasite in potassium permanganate will cause it to release it's hold somewhat making removal easier.
Once removal has been achieved, a salt dip and antibacterial treatment of the area should be undertaken.