This is an invasive parasite, originally described from the Far East, but which is now known from the wild in countries across Europe, North America, Africa and even Australia.
It is suspected that it has been transported around the world unintentionally, with stocks of ornamental fish, particularly koi carp. It has been found on a wide range of freshwater fish species and appears to have low host specificity.
Argulus japonicus is an unwelcome invasive species. Fish stocks for translocation should be checked for the presence of parasites such as fish lice.