The family name Lernaedae belongs to only one genus Lernaea the anchor worm so called because the head of the parasite develops into an anchor like projection under the skin of the host to prevent its removal. The anchor worm is a true parasite, in that it embeds in either the gill or body of the host and its food source is the tissues of the host, unlike most common parasites that attach to the fish and feed on any dead matter or bacteria that that happen to pass by. in this way Lernaea causes immense tissue damage.

Lernaea has an extremely complex and fascinating life cycle worthy of some study.

For the hobbyist it's a case of good news, bad news, the good news being that diagnosis is easy as the parasite is so large it can easily be seen with the naked eye as the fish swim past, the adult anchor worm can measure up to 8 mm in size. The bad news is that as an organism it is extremely resistant to chemicals and can be hard to be eliminate.

Lernaea belongs to a genus class called Copedoda and are crustaceans, related to lobsters, crabs, it's life cycle is amazingly complex and goes through many stages of metamorphosis, needing to shed its outer skin to increase in development and size, starting as a newly emerged hatchling a few microns in size to an adult measuring up to 8 mm in size.

The easiest gender to deal with from the literary point of view is the male Lernaea as this never gets beyond the sixth metamorphosis stage. Both genders reach sexual maturity at the sixth stage and then mating occurs.
The male having developed testes at stage six will deposit two sacks called spermatophorse on the genitalia of the female and then fall away and die, his life cycle complete.
In general the metamorphosis stages of both genders are very similar up to the sixth stage and the death of the male, then the female goes on to embed into the host. We can see from this, that all Lernaea found embedded on the host are female and only female.

The cycle begins with the newly emerged hatchling called the Nauplii,( pronounced "no-pLE-eye") which is oval in shape measuring about 150 micron in length, after 2/3 days this stage will moult and morph into the next stage the metanauplii, which is a little larger, as with the Nauplii it has an exoskeleton made of substance called chitin (pronounced as "kI-tn").
The first thoracic stage will be seen about 2 days after the metanauplii is created, shortly after this the first copepod
stage(pronounced "kO-p-pod") will be formed measuring about 250 micron with two pair ofswimming legs, its at this point the newly formed copepod must seek out a host within 2/3 days or perish. While on the host Lernaea continues morphing up to the fifth stage, gaining a thoracic section with a pair of legs on each section. At the sixth stage Lernaea attains sexual maturity, the female gaining ovaries and the male gaining testes, at this point mating (copulation) occurs, as stated above the males drops off the fish and dies.
The females continues to develop, growing in length and will then thrust her head into the living flesh of the host. Once embed into the host the head starts to develop projections called, cephalic horns, making removal of the Lernaea very hard. The eggs sacks move rearward to the end of the body resembling legs. Interestingly, the females have no further use of legs so these will shrink and eventually vanish leaving a slender body form with the egg sacks at the rear of the parasite in a classic upside down Y or wine glass shape. Lernaea will now be completely immobile.Once the eggs are mature they will be shed into the water and the life cycle begins again


Treatment is very hard, as it will involve the capture of the host (koi) and the physical removal of the parasite with tweezers, taking care not leave the embodied head of the Lernaea in the flesh of the koi, as this will lead to secondary bacterial infection which can sometimes be life threatening.
It has been reported that dabbing the parasite with potassium permanganate will cause the parasite to release her grasp on the host, enabling easy removal, personally I have never tried this but it is thought extremely unlikely, as Lernaea have no voluntary control over the head projections. Once the head and body is removed treat the site with Mercurochrome, betadine or similar then treatment can begin on the pond.

Masoten @ 1gm per 87 imperial gallons per week for four weeks at a pond temperature of 65F/18.3C should get all life stages. below 65 deg 6/8 gm per 1000 imperial gallons

Lernaea will die in a 1.8% salt solution for 20 mins. Lernaea die when not immersed in water and become dehydrated, so whilst moving the fish to a quarantine system for salt dips and drain the pond to allow for
cleaning and drying out for 24 hours if you have trouble getting hold of Masoten

The life cycle of Lernaea cannot be completed at temperatures below 15 c and below 8 c metamorphism cannot take place and lava and adult will die over winter.