Freshwater Fish:
* Mucous layer: A protective layer of mucus covers the skin, acting as a barrier against water loss.
* Kidneys: They produce large amounts of dilute urine, which helps to flush out excess water.
* Gills: They actively absorb salts from the surrounding water, helping to maintain a balance of electrolytes.
* Lower osmotic pressure: Their body fluids have a lower concentration of dissolved salts than the surrounding water, which helps to prevent water from diffusing out.
Saltwater Fish:
* Scales: Their scales provide a physical barrier against water loss.
* Gills: They actively excrete excess salts through their gills.
* Kidneys: They produce small amounts of concentrated urine, conserving water.
* Higher osmotic pressure: Their body fluids have a higher concentration of dissolved salts than the surrounding water, which helps to prevent water from diffusing out.
Other adaptations:
* Behavioral: Some fish may burrow in the mud or hide in shaded areas to reduce water loss.
* Physiological: Some fish have special adaptations, like the ability to store water in their bodies, to help them survive in dry environments.
Overall, fish use a combination of these adaptations to minimize water loss and maintain their internal environment. The specific adaptations vary depending on the species and their environment.