- No silly, they don't get thirsty living in waterVote A
- Yes they do, better give the fish a beerVote B
Most Helpful Girl
Of course they do
Most Helpful Guy
Credit goes to a reddit user who posted this in r/nostupidquestions. It's copy paste of majority of his answer.
It all comes down to osmosis. Say you've got a bucket of water with a thin film separating the halves, and you put salt in one half. If the film allows water to travel through, but not salt, then water will move to the salty side to try and equalise the concentraiton (very ELI5 explanation)
So fresh water fish do not get "thirsty", because water is constantly being absorbed by them due to osmosis (inside of fish is saltier than water). In fact, they end up having to urinate... a lot.
Salt water fish on the other hand can have the opposite issue. The outside water is saltier than their body. So water from their cells will end up being transferred out, and so they have to drink a bunch!
TL;DR: Salt water fish drink lots, Fresh water fish barely drink anything, but piss more than a drunken sailor3