Question

When a salmon or other teleost fish migrates from seawater into freshwater, what are all the changes that take place or are likely to take place in its patters of water-salt physiology?

Answer 1

Salmon fish is adapted to live in both salt water and fresh water by the process called osmoregulation i.e., regulation of ions and fluids across the membrane of an organism according to the changes in the environment where it lives.

There are three physiological changes seen in the fish in salt water and fresh water

FRESHWATER	SALTWATER
the fish gill has molecular pumps that regulate sodium-chloride pumps according to the need of the body by ATP expenditure In the freshwater, salmon pumps in Na and Cl ions to regulate the concentration in and out of the cell because freshwater has very minimum amount of ions, so in order to meet its expenditure the gills epithelial cell takes in Na And Cl ions by the enzyme Na+ Cl- ATPase	The molecular pumps in case of salt water pumps out sodium and chloride ions as the concentration of chloride and sodium is three times concentrated than the ions present in its body fluids by the enzyme Na+ Cl- ATPase
Salmon do not drink water as it is already swimming in the freshwater	Salmon needs to drink water and pump the sodium and chloride ions out to prevent dehydration
It excretes large volume of urine which is hypo-osmotic to its blood plasma means	it excretes less urine which is iso-osmotic to the blood plasma