Do fishes get thirsty?

We don't know if fish experience thirst as a sensation, but they do need water and they deal with this need in different ways. Some fishes actively drink water, others don't.

First, it's kind of obvious but well, fish normally live in water, and water naturally tends to flow toward the solution in which its concentration is lower, that is to say, toward the solution in which the concentration of salts, etc. is higher. The concentration of salts is higher in sea water, intermediate in animal's bodies, and lower in fresh water, and this is important to understand the following:

Those fishes living in the sea or high-salt concentration waters are constantly losing their body water to the environment (mostly through their gills), and need to drink it. These fish have well developed special glands to get rid of the salt in the water that they drink.

In contrast, in freshwater fishes, whose body is more concentrated than the surrounding water, water will tend to enter their bodies - so their problem is not lack of water but rather how to get rid of the excess!

Also, this only applies to bony fish. Sharks and their kin have different mechanisms to avoid water loss or gain.

Fishes swim in water and do not sweat a lot, conserving moisture. They can get all the fresh water they need by breaking down carbohydrates (carbon and hydrogen) using oxygen to produce carbon dioxide (CO2) and water (H2O). Even humans produce such metabolic water (although many get thirsty for soda or beer, etc.). Human blood is rather saline and it is said that it simulates the sea (where all life likely began).

Yes !!, Fish also get thirsty.

We do drink water for to consume minerals or salts for the body requirement espp. for muscles. As like us he fishes also have the muscular body structure and for to move in the water, the fish needs the help of muscular movement and for that movement fish needs the minerals ions to full-fill the body requirement after certain period of time and these minerals are present in the water. So the Fishes gets these salts or minerals from the water through their skin.

Minerals plays an important role in moving muscles and to they are the responsible to generate action potential across particular muscle to move thats why we need water and fishes needs also water.

NOTE:-

100 % Pure water is not good for health. So consume mineralised water.

They do if they are out of water, that's why you should always offer a refreshing drink to a fish that's visiting you.

Yes, thats why you have to keep adding water to the tank.