What is anchor worm?

Anchor worm is a parasite of the skin and gills of fish. The parasite was first found in the Canning River in 2008 and has since been found in the Serpentine and Murray Rivers, south of Perth. Although originally a parasite of goldfish and carp, anchor worm has a very wide host range. It has been found on more than 45 species of freshwater fishes throughout the world. Infections in native fishes cause large wounds, bleeding, castration and high death rates.


Anchor worm profile

Anchor worms mate during the last stage of their development. After mating, the female burrows into the flesh of the fish host and attaches with an anchor-like process on the head. This leaves the unsegmented, wormlike body protruding from the skin or gills of the fish.


How is anchor worm spread?

Anchor worm was probably introduced through the accidental or deliberate release of freshwater fishes, such as goldfish and carp. There are currently 13 – 15 species of introduced freshwater fishes in rivers in the south-west of Western Australia.


Is this a problem for native freshwater fishes?

Anchor worm causes Lernaeosis, a parasitic disease of freshwater fishes. Anchor worm is much more capable of causing disease in native freshwater fishes than in its natural hosts, goldfish and carp. This is because native freshwater fishes have limited defence behaviour and a weak immune response.

In general, introduced freshwater fishes are predators of native fishes, compete with native fishes for food, decrease water quality and introduce diseases. Anchor worm poses a significant additional threat to native freshwater fishes in the south-west of Western Australia, where 82% are unique local species and 55% of species are endangered.


What can we do about alien parasites of native freshwater fishes?

In an open, natural river system it is not feasible to eliminate anchor worms. The only way to stop the spread of this parasitic disease is to:

  • Stop releasing ornamental fishes, such as goldfish or carp into rivers, lakes or waterways.
  • Report fishes with parasites to WA PestWatch at www.fish.wa.gov.au.


Did you know:

  • Anchor worms are not actually worms, they are a freshwater copepod. A copepod is small crustacean found in nearly every freshwater habitat.
  • Only the female anchor worm attaches itself to the fish. The male attaches itself to the female.
  • The parasite is named after its anchor shaped head, which burrows into the muscles of the host.


Download the ‘Anchor Worm and Native Freshwater Fishes’ information sheet.


infected-pygmy-perchInfected pygmy perch.
Photo: Fish Health Unit, Murdoch University.