Animals are able to live because they are osmoregulators. This allows them if they are in freshwater to adjust where the osmolarity is too low for support of cellular life or on land where the water is in a shorter supply. Thus the osmoregulation is costly, based on how many different animals osmolarity are in their surroundings. Also it depends on how much of the membrane transport work is required to actively transport solutes. The osmoregulation makes up almost five percent of the resting metabolic rate of freshwater bony fish and many marine animals.
Some animals use up to thirty percent of their resting metabolic rate.
Both the osmoregulators and osmoconformers are not able to handle the external osmolarity. Animals that are like this are known as stenohaline. Yet animals known as euryhaline, which means they survive radical fluctuation in the osmolarity in their surroundings. They will either conform to the changes or regulate to their internal osmolarity within a narrow range even as the external osmolarity changes. All the freshwater animals and may other marine animals are osmoregulators, which means they maintain their internal osmolarity that can differ from the surrounding water.