Almost all freshwater animals and most marine vertebrates are:

Explanation

Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content. Freshwater fishes absorb a controlled amount of water through the mouth and the gill membranes. Due to this intake of water, they produce large quantities of urine through which a lot of salt is lost. The salt is replaced with the help of mitochondria-rich cells in the gills.Osmoconformers are marine organisms that maintain an internal environment which is isotonic to their external environment. This means that the osmotic pressure of the organism's cells is equal to the osmotic pressure of their surrounding environment.