Have you ever wondered whether fish drink or not? All living things must drink, and they require a fresh
supply of water. A person can go without food for many days, but he or she cannot go for long without
water. Fish drink, and fish that live in salt water must drink salt water. However, when we watch them in an
aquarium and see them opening and closing their mouths, we must not assume that they are drinking. Fish
need water for its oxygen. The water that they seem to be gulping gives them oxygen, which is in the water.
On the other hand, when a fish drinks, it swallows water, just the way we do.
It is stated in the passage that a fish opens and closes its mouth