Chum salmon (Oncorhynchus keta) are born in freshwater environments and then migrate to the sea. Near the end of their lives, they return to the freshwater stream where they were born to spawn. In fresh water, water constantly diffuses into the body and ions are lost from the body. In salt water, body water diffuses out of the body and excess ions are gained from the water. A salmon's gills have special cells to pump salt in or out of the body to maintain homeostasis. In response to the salmon's moves between fresh water and salt water, some cells in the gills are produced and others are destroyed. These changes made in the cells of the gills during the lifetime of an individual salmon are an example of which of the following?

A) evolution
B) trade-off
C) acclimatization
D) adaptation
E) luck

Acclimatization is the change in the body of an organism in response to changes in the environment to maintain equilibrium (homeostasis). In the case of the salmon, when the environment changes from fresh to salt water and back, the chemical homeostasis would be altered if the fish didn't adjust. The adjustments in the fish gills are the response of the fish to acclimatize to the changes in the chemical environment in order to maintain homeostasis.