Do fish need to drink, ie - do they swallow water, like we would drink a glass of the stuff?
I think they’re constantly drinking when they breathe, but I’m not sure. So:
How do they ‘drink’ and is the phrase ‘drink like a fish’ based on an assumption?
Fish breathe by taking in water through their mouths and then expelling it through their gills. So if you count “drinking” as just taking water into your mouth, then yes, fish “drink” constantly. I have no idea if they have to swallow any, though.
I have heard that salt water fish do have to drink, fresh water fish don’t. Something to do with Osmosis & salt water, but I may have the two mixed up now that I think of it.
In freshwater, the inside of the fish is saltier than the outside, so water is constantly migrating through its tissues towards the middle. Freshwater fish are constantly… well… piddling, I guess. In saltwater though, the water is saltier than the inside of the fish, so water is constantly migrating out of the fish. These fish gulp water to counteract that. This is why you can’t put a freshwater fish in saltwater, etc. Totally different physiologies. The exception are migratory fish like salmon, who undergo radical transformations during their swims.
From the shark phase years ago (Jaws, etc.) I remember reading that a shark must continually move thru the water…water in and water out…or it will die.
Again, that’s analogous to breathing, not drinking (and it isn’t true of all sharks).
Yup, just learned this in my marine biology class. They drink the salt water then excrete the salt through their gills. It’s called osmoregulation.