Marine Parasitology studies fish parasites in all parts of the world Oceans. One of the less studied ecosystems on earth is the deep sea. The deep-sea is characterized by an absence of sunlight, low water temperatures, high hydrostatic pressure, weak water currents, and scarcity of food. The principal factors determining the settlement of organisms are food availability and water movement. Expensive research expeditions are needed to get access to the unique research material.
Also the deep-sea inhabits a rich parasite fauna, consisting of all major taxa. In total, 421 of the 3800-4200 known deep-sea fish species (less than 10%) have been studied for its metazoan parasites so far. These hosts harbour 621 different parasite species. It has been estimated that between 1.5 to more than 3 different metazoan parasite species can infest each single fish species also in the deep-sea environment, leading to the assumption that between 5-10,000 parasite species occur below 200 m water depth.