Feeding in Adult

The argulids are an economically important group of crustacean ectoparasites known to be problematic in fish farming operations from both temperate and tropical regions. Argulus japonicus was first described from Japanese fish but is now well established in many parts of the world including Europe. To aid the development of effective chemotheraputants and/or vaccines against these parasites it is essential to know exactly what these animals ingest when feeding upon their fish hosts. From past morphological studies authors have shown that these parasites use a proboscis-like mouth tube for feeding, however, until now there has been much speculation amongst authors over the diet of these animals. Live observations, histology, as well as scanning and transmission electron microscopy were used to examine the feeding apparatus and gut contents of individual larval and adult lice before and after feeding on juvenile common carp, Cyprinus carpio. Red coloration of the parasites gut after feeding was obvious, suggesting ingestion of red blood cells by the adult lice. Sections of the adult lice used for histology and TEM revealed red blood cells from the fish host within the parasites gut. Larval lice were found not to feed on blood cells because of their mouth part morphology and the lack of blood cells in their intestines. Haemorrhagic responses of the hosts skin by infection of adult lice was observed between 24 and 48 hrs post infection. All techniques provided evidence that the adult parasites are indeed obligate blood feeders.