Question

Salmon eggs hatch in fresh water. The fish then migrate to the ocean (a hypertonic solution) and, after several years of feeding and growing, return to fresh water to breed. How can these organisms make the transition from fresh water to ocean water and back to fresh water?

		Salmon in fresh water excrete concentrated urine, and salmon in salt water secrete dilute urine.
		The rectal gland functions in the ocean water, and chloride cells function in fresh water.
		The salt transport mechanisms of the gill epithelia change during migration.
		Their metabolism changes in salt water to degrade electrolytes.