Question

Osmoregulation in marine fishes is achieved by

• A. drinking water from the surroundings and excreting dilute urine
• B. drinking water from the surroundings and excreting concentrated urine
• C. actively absorbing ions through gills
• D. not drinking water at all

Answer 1

The correct option is B drinking water from the surroundings and excreting concentrated urine

Osmoregulation refers to the process of maintaining a constant osmotic concentration in the body of an organism, irrespective of the changes in osmotic concentration of its surroundings. It is of utmost significance in the survival of organisms which live in water.

Marine fishes live in hypertonic water. That means, the water has higher concentration of salts compared to that of the cells in the fish. This indicates that the relative concentration of water within the cells of the fish’s body is comparatively higher than that of the surrounding solution (sea or ocean water). This causes water from the fish's body to move out into the surroundings via exosmosis. This can lead to an osmotic imbalance.

To maintain a constant osmotic concentration, the marine fishes show the following adaptations :

• Drinking seawater to compensate loss of water through gills. So option d is incorrect.
• Actively pump out the salts ingested along with water through gills. Hence option c is incorrect.
• Excrete concentrated urine to compensate for water loss and surplus salts. Thus, option b is correct and option a is incorrect.

Figure : Osmoregulation in marine fishes