Ammonotelism - Excretion
Ammonia diffuses through cell membranes extremely fast because of its high water solubility and small molecular size. Hence, it can be excreted as such only when there is ample water for its rapid removal from the body in the form of a dilute solution. Prompt excretion of ammonia therefore, occurs in aquatic animals, both freshwater and marine, in which there are constant water fluxes occurring between the environment and the body.
Freshwater and marine invertebrates and fishes, larval and permanently aquatic amphibians excrete a major portion of their waste nitrogen as ammonia and thus called ammonotelic or ammoniotelic. The route of ammonia diffusion in these animals is skin, gills or kidneys.