Do fish ever get thirsty?
The Real Answer
For many common bony fish, freshwater and saltwater environments create opposite water-balance problems. Freshwater fish generally take in water through osmosis and produce relatively large amounts of dilute urine, so they typically drink much less water. Many marine bony fish lose water to their saltier surroundings and compensate by drinking seawater, then removing excess salts through specialized processes involving their gills, kidneys, and digestive system. But this isn't a rule for every fish, and whether fish experience a conscious sensation comparable to human thirst is a separate question that isn't established simply by observing whether they drink.
You watch a fish spend its entire life surrounded by water and still ask whether it gets thirsty because your brain refuses to separate 'water everywhere' from 'water balance.' You keep trying to give the fish your rules even when the fish lives under completely different ones.
The Dunce Dynamics Institute Examines Why People Ask This
The question feels paradoxical because a fish can be surrounded by water and still face a water-balance problem. The useful distinction is between physiological drinking and the separate, harder question of whether a fish consciously experiences thirst.