Final answer:
Osmoregulators maintain their internal water and salt balance via physiological mechanisms, adjusting to conditions in both freshwater and saltwater environments with processes like active transport, osmosis, and the monitoring of solute concentrations by osmoreceptors, with the kidneys playing a key role in mammals.
Step-by-step explanation:
Osmoregulators use a variety of physiological mechanisms to maintain optimum salt concentrations in their tissues, regardless of the salinity of their surroundings. Osmoregulation is the process whereby organisms maintain their internal water and salt balance across their cell membranes. Essentially, this process allows an organism to regulate its bodily fluids, thereby ensuring its osmotic balance regardless of the external environment. Fish are classical examples of osmoregulators that have developed different strategies to survive in both freshwater and saltwater environments. Freshwater fish face a hypotonic environment and tend to excrete a large volume of dilute urine, while saltwater fish live in hypertonic conditions and excrete excess salts.
Animals such as salmon that can live in both types of environments switch their osmoregulatory strategies in response to hormonal signals which trigger adaptive changes for each habitat. Organisms achieve osmoregulation through several mechanisms, including active transport of electrolytes, water movement through osmosis, and the function of osmoreceptors that monitor solute concentrations in blood. The kidneys, owing to their complex structure, play a key role in osmoregulation in mammals, filtering the blood and adjusting water reabsorption according to the body's needs.