Final answer:
Aquatic animals release ammonia into the water to eliminate it, while terrestrial animals convert ammonia into urea or uric acid.
Step-by-step explanation:
Aquatic animals, such as fish, eliminate toxic ammonia by releasing it into the water. Ammonia is a highly toxic base that, if accumulated in the body, would quickly be fatal. On the other hand, terrestrial animals have evolved different mechanisms to excrete nitrogenous waste, such as converting ammonia into urea or uric acid, which are relatively non-toxic forms. The production of urea and uric acid requires more energy and is more complex than the excretion of ammonia in aquatic animals.