How do freshwater fish adapt to their environment regarding salt content?

Freshwater fish are adapted to their environment by having a physiological mechanism that allows them to retain salt while excreting excess water. In freshwater, the concentration of salt in the water is lower than that inside the fish's body, creating a situation where water naturally tends to move into the fish's cells through osmosis. To counteract this, freshwater fish have specialized cells in their gills called chloride cells that actively absorb salts from the surrounding water, which helps maintain their internal salt concentration.

Additionally, since they live in an environment where they are constantly gaining water, they produce large volumes of dilute urine to excrete this excess water while conserving salts. This adaptation is crucial for their survival, as it helps maintain homeostasis and prevents the dilution of their internal salt levels that would otherwise occur in such a dilute environment.

Through this mechanism of actively retaining salt and excreting water, freshwater fish effectively balance their internal osmotic pressures to thrive in their aquatic habitats.