What kind of mechanism allows the salmon cells to adapt to freshwater after leaving saltwater?

Salmon adapt to freshwater after leaving saltwater through a mechanism involving ion regulation and osmoregulation. In saltwater, their cells face dehydration due to higher external salinity, requiring them to actively excrete salt ions through specialized cells in their gills. Upon entering freshwater, salmon switch to absorbing ions and retaining water, utilizing different ion transport mechanisms to maintain osmotic balance. This adaptive response is facilitated by changes in gene expression and the functionality of ion transporters in their gills and kidneys.