As humans, we need to drink water constantly to survive. But what about fish? They live surrounded by water – so do they need to drink it too?
The answer is more complicated than you might expect.
Fish absorb water through a process called osmosis.
Put simply, osmosis is when water moves across a barrier from an area of low concentration to an area of high concentration to balance things out.
For fish, this happens across the membranes of their cells and bodies.
Freshwater and saltwater fish have different osmotic challenges.
Freshwater fish live in water with hardly any salt, while their bodily fluids are much saltier. That means water is constantly moving into them.
To maintain balance, freshwater fish pee a lot and have special cells in their gills to pump out excess salts.
On the flip side, saltwater fish live in very salty ocean water. That makes the water in their bodies seem fresher by comparison.
As a result, they constantly lose water through their gills. That’s why saltwater fish drink water on purpose – they gulp it down continuously to stay hydrated. Their kidneys also work extra hard to filter out salt.
It’s a constant battle for fish to maintain the right internal salt and water balance. Too much water flowing in or out causes problems.
In a way, the challenges fish face living in water mirror problems we humans have staying hydrated on land!
As an experiment, soak some potato slices overnight in fresh water versus salt water to visualize osmosis for yourself.
The saltwater potato will stay firm, while the freshwater one absorbs more water and turns soft.
So, while fish don’t sip water from a glass like we do, make no mistake – they still need to take in water constantly.
Osmosis handles some of their needs, but especially for ocean fish, conscious drinking is a must.
Have more questions? Come on, ask us.
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