Fish Louse

Fish lice are ectoparasites that infest marine and freshwater fishes. Unlike other blood-sucking invertebrates bearing the common name of louse, the fish louse is more closely related to lobsters, shrimp, and water fleas than they are to insects such as the human head or body louse. However, in an analogous fashion to true lice, members of the crustacean genus Argulus pierce the skin and inject digestive enzymes into the host with a highly modified mouthpart known as a stylet. Subsequently, the parasitic insects then suck out blood, mucus, and partially digested body fluids.