The excretion of ammonia and ammonium ions is calles ammonotelism.
The organisms which excrete by ammonotelism are known as ammonotelics.
The main product of excretion is ammonia, which is toxic and should be removed from the body as soon as it is formed. Ammonia is higly soluble in water. Hence, all ammonotelics are aquatic animals.
Examples: fish, amphibian larve, etc.