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

Argulus japonicus ingests blood from its hosts passing it along branching lateral sections of the gut which extend into the carapace on each side of the body.