@TheGlitchedWolf
Technically yes, let’s dive into biology first, when you’re thirsty, it isn’t just about you lack of water in your body, but it’s more of the imbalance of electrolytes (important mineral) and water. When you’re let’s say running for example you lose both water and electrolyte, but you lose water faster, hence the ratio between electrolyte and water is increase and at certain point you feel thirsty, it’s basically your body telling you “Hey, you have too much electrolyte compare to water here, you need to drink more”. On the other hand you can also be thirty by drinking water, specifically salty water. Since one of the electrolyte is sodium and salt is made out of sodium and chlorine. So when you drink a lot of salty water like sea water, you will pee more since your body want to keep the balance. Hence the more you drink sea water the thirstier you become.
So how fish get thirsty? well first there is two type of fish, seawater fish and fresh water fish. For seawater fish, just put them in the fresh water. While the fresh water fish put them into sea water, sooner or later it will create the imbalance between electrolyte and water in their body. And they got thirsty. But please don’t do this, you basically killing the fish slowly and painfully.