A. Generalities 1. Solutes give water osmotic pressure. In sea water, animals face the problem of constantly losing water and gaining salts. In fresh water, animals face the problem of constantly losing salts and gaining water.
Terrestrial organisms have the problem of locating and retaining water.
In terrestrial animals, water comes in via drinking and exits via urine, feces, perspiration and breathing. In fresh water aquatic animals, water comes in through gills and exits through urine and feces. B. Principal Organs of Osmoregulation 1. Salt gland 5. Regulating amount of water in body, retaining or getting rid of it, depending on animal's needs.