Ammonotelismi

Ammonotelismi is a form of nitrogenous waste excretion observed in many aquatic animals. These animals, known as ammonotelic organisms, excrete nitrogen in the form of ammonia. Ammonia is a highly toxic compound, but it is also very soluble in water and requires little energy to produce. This makes it an efficient waste product for organisms living in aquatic environments where they can easily dilute and excrete it.

Fish are a primary example of ammonotelic organisms. They release ammonia directly into the water through their gills. The high concentration of ammonia in their body fluids, relative to the surrounding water, drives its diffusion out of the fish. Other aquatic invertebrates, such as many crustaceans and some larval amphibians, also exhibit ammonotelism. The survival of these animals depends on a constant supply of fresh, circulating water to carry away the ammonia.

The evolutionary advantage of ammonotelic excretion lies in its low metabolic cost. Producing urea or uric acid, the nitrogenous wastes of ureotelic and uricotelic animals respectively, requires more energy. Therefore, ammonotelismi is favored in environments where water is abundant and waste dilution is not an issue. Animals that have adapted to terrestrial life or environments with limited water typically evolve away from ammonotelismi to conserve water and reduce toxicity.