Why fish swallow water?

Fish don't swallow water to quench their thirst like we do. Instead, they swallow water for a couple of reasons:

* Respiration: Fish use their gills to extract oxygen from the water. Water flows over the gills, and the oxygen diffuses into the fish's bloodstream. This process is called buccal pumping and it requires the fish to actively pump water over their gills.

* Maintaining buoyancy: Fish have a swim bladder, a gas-filled sac that helps them maintain their buoyancy in the water. Swallowing water helps adjust the amount of gas in the swim bladder, allowing them to sink or rise as needed.

Here's how it works:

1. Mouth opens: The fish opens its mouth and takes in water.

2. Water flows over gills: The water is then passed over the gills, extracting oxygen.

3. Water exits: The water exits the fish through the operculum (gill cover).

4. Swim bladder adjustment: Some of the swallowed water might be used to adjust the swim bladder's volume.

So, while fish don't drink water like humans do, they do need to swallow it for vital functions like breathing and maintaining their position in the water.