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Gill Maggot (Ergasilus)

Gill maggots (Ergasilus) are parasitic crustaceans, named after the egg clumps that resemble maggots. The incidence of gill maggots has been greatly reduced, and this crustacean is seldom experienced by the hobbyist. If untreated it can cause major gill damage and result in large fish losses. The gill maggot is closely related to anchor worm (Lernaea) but is mainly found on the gills, gill covers and the mouths of infected koi. The gill maggot is a blood sucker and anaemia can result from an infestation. The most damage however is done to the gill filaments which bring about the most mortalities. When spotted, steps should be taken not only to eradicate the adults that are seen on the koi, but also any juvenile stages that are present in the water.  




The life cycle of the gill maggot starts when the females attack the gills of the host koi these females produce egg sacks and once these egg sacks have released the eggs into the pond, free swimming juveniles will hatch within a few days. They will then continue to develop until a suitable host is found. Once attached to a host mating will take place. Soon after mating, the male parasite will perish and the female will attach to the gills of the host, where she will start producing eggs. This way the cycle will repeat itself. The female can live for a considerable time on a host if left untreated. It is unsure how long juveniles can survive without a host but the development that it must go through suggests that it may be for several days.






Off the shelf treatment is available from some dealers but the most effective way of treating the adults and juveniles in a pond is with organophosphate. Remember that organophosphate is an insecticide that will kill all other crustaceans in the pond. Repeated treatments will be required to eradicate juveniles when they hatch.

Last Updated on Friday, 05 November 2010 17:33