Freshwater Fish:
- Freshwater fish live in a hypotonic environment, where the concentration of dissolved particles (mainly salts) in the surrounding water is lower compared to the concentration of particles within their body fluids.
- To prevent water from entering their bodies through osmosis, freshwater fish have evolved several adaptations:
- They possess a relatively impermeable skin and specialized structures called chloride cells in their gills that actively transport salts from the water into their bloodstream, maintaining a higher internal salt concentration.
- Their kidneys play a vital role in regulating water and ion balance by selectively reabsorbing water and excreting excess salts.
- They have a reduced production of urine compared to marine fish to conserve water.
Marine Fish:
- Marine fish live in a hypertonic environment, meaning the concentration of dissolved particles in seawater is higher than that of their body fluids.
- To prevent water loss through osmosis, marine fish have different adaptations:
- They drink large amounts of seawater and actively absorb needed salts from it through specialized cells in their gills and intestines.
- Their kidneys are modified to excrete excess salt and concentrate urine to conserve water.
- Their skin is less permeable to water compared to freshwater fish.
In summary, freshwater fish must actively prevent water from entering their bodies, while marine fish must conserve water and actively absorb salts from the surrounding seawater to maintain water balance and proper physiological functions.