It probably depends on whether its a freshwater fish or saltwater fish.
Freshwater fish don't need to drink - they can absorb water through osmosis because the water they live in is less salty than the water inside their cells. To avoid taking in too much water, they pee out the excess water frequently.
Salt water fish have to drink water on the other hand because the water in the ocean won't diffuse into a less salty environment inside the fish's cells. Therefore they have to drink water and pee out the excess salt.
We evolved thirst to tell us when to find water to avoid dehydration. Therefore, its possible that saltwater fish sense thirst while freshwater fish don't.
Click Here to return to the search form.