Salmon's Amazing Adaptation: Thriving in Both Fresh and Salt Water
2025-05-31
Salmon face a remarkable physiological challenge: they mature in the ocean but spawn in freshwater streams. This means adapting to drastic environmental changes between saltwater and freshwater. To cope, salmon have evolved impressive physiological mechanisms. In saltwater, they drink copiously to replace lost water, their kidneys produce concentrated urine to excrete excess salt, and gill Na+-Cl- ATPases pump salt out of their bodies. In freshwater, they stop drinking, their kidneys produce large volumes of dilute urine, and the gill pumps reverse, absorbing salt from the water. This adaptation isn't instantaneous; salmon require days or weeks to transition between environments.