Argulus japonicus

Argulus japonicus is a fish louse (a branchiuran crustacean) living as a parasite in a wide range of freshwater fish hosts.

An invasive species, originally from the Far East Argulus japonicus is now found in the wild across Europe, North America, Africa and even Australia. 

Fish stocks for translocation should be checked for the presence of parasites such as fish lice.

Species detail

Argulus japonicus has a retractable poison spine in the front of its mouth.

Argulus japonicus feeds by

  • injecting toxin into the host from its poison spine
    • the toxin 
      • irritating the fish 
      • and beginning the process of pre-digesting the tissues
  • taking the digesting tissue into the mouth tube using mandibles 
  • swallowing
  • Adult Argulus showing suckers

    Learn about the size and structure of Argulus japonicus, find out about similar looking species as well as the wider family to which this species belongs.

  • Argulus japonicus larva

    It is suspected that Argulus japonicus has been transported around the world unintentionally, with stocks of ornamental fish. Discover the areas of the world that this species is currently known from and find out about its feeding patterns.

  • Argulus japonicus eggs

    Read about the reproductive processes and lifecycle of Argulus japonicus.

  • Argulus japonicus

    Find out more about how Argulus japonicus uses a poisoned spine and toxin to feed on fish hosts.

  • Argulus japonicus in its host

    Get reference material for Argulus japonicus.


Argulus japonicus in its host

Argulus japonicus parasitises a wide range of freshwater fish hosts.

Adult Argulus showing suckers

Adult Argulus attach to the host by means of a huge pair of modified suckers.

Argulus japonicus larva

Argulus japonicus larva

Argulus japonicus eggs

Argulus japonicus eggs

About the author

Geoff Boxshall
Prof Geoff Boxshall

Merit Researcher in the Crustacea Research Group, focusing on patterns of diversity in copepods and the biology of parasitic copepods from fish and marine invertebrate hosts.

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