Abstract
Significance of parasitology on marine mammal studies was summarized based on several aspects, i.e.faunal studies on parasites, utility of parasites as biological indicators and the pathobiology of parasitic diseases. Faunal studies on parasites are of an essential of marine mammal parasitology. Comparing the data with those from the different waters, not only distribution and host range of parasites will be understood, but also a useful biological indicator may possibly be found out. Many works have been accumulated from the world seas to date, however faunal studies have not yet been completed, especially in the waters around Japan. Extensive standing surveys will be needed to list parasites of marine mammals of Japan. Parasites have been used as biological indictors to mainly analyze stock structure, in several aquatic organisms including marine mammals. The life cycles of parasites are restricted by the biological characteristics of the hosts, which are often exhibited by parasites. However, the information on the life cycles of marine parasites is quite limited. The role of parasites as pathogens in the natural mortality and stranding of marine mammals is an unavoidable discussion. Many pathological changes derived from the parasite infestations have been reported and several parasites were pointed to be fatal pathogens. Digeneans of the genus Nasitrema, reside in the cranial sinus of small cetaceans, are of the examples that are thought to cause of death and stranding.
