Some of the known types of parasitic relationships, or parasitism, include isopods who attach themselves to fish while feeding on their bodies. Isopods are basically fish lice that the fish are unable to get rid of.
Parasitism occurs everywhere in the natural world, and the ocean is no exception. In addition to fish falling victim to parasites, the large mammals of the sea, such as whales, are also taken advantage of and used for their resources. Many large mammals have intestinal parasites that feed on nutrients from the food that the whale consumed. Parasites attach to their victims and may even kill them by depleting them of energy.