If a marine fish is placed in a fresh water aquarium, then its chances of survival will diminish. This is because their bodies are adapted to high salt concentrations of the marine environment. In fresh water conditions, they are unable to regulate the water entering their body (through osmosis). Water enters their body due to the hypotonic environment outside. This results in the swelling up of the body, eventually leading to the death of the marine fish.



Points to remenber

■ To maintain osmolarity


● For fresh water

• Do not drink water
• Excrete hypotonic urine
• Active absorption of ions by chloride cell, which are present in gills.

● For sea water

• Drink water 
• Excrete hypertonic ions
• Actively pump out ions by chlorine cell which are present in gills.