Do fish drink water

fish drink water

Do fish drink water

Fish do consume water and need it to survive just as humans do. But fish don’t necessarily drink it as a human drinks a glass of water.

Fish consume water through a process known as osmosis. Merriam-Webster defines osmosis as “movement of a solvent (such as water) through a semipermeable membrane (as of a living cell) into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane.” 

In simpler terms, osmosis is the process of something passing through a thin sheet to alter and balance a substance in something. Fish absorb water through gills through the process of osmosis, essentially being their equivalent to drinking water.

Do all fish drink water through osmosis?

Not all fish drink water solely through osmosis. According to McGill University, saltwater fish consume water not only through osmosis but also purposefully drink water to have some go through the digestive tract. Water does end up going into freshwater fish’s mouths, but instead of swallowing it, the water is filtered out through the gills.

Why are freshwater fish unable to consume freshwater? 

Freshwater fish don’t require water via their mouths to survive, unlike their saltwater counterparts. 

According to McGill University, the blood and body fluids of freshwater fish are saltier than the water in which they swim. According to McGill University, “fishes’ bodies, just like ours, need a particular concentration of salt to function best.” A freshwater fish’s internal balance may become awry if it swallows freshwater. 

Depending on where they live, fish either drink a lot or pee a lot. In the sea, a fish’s body is less salty than its surroundings, so it loses water across its skin and through its gills via osmosis. To stop themselves dehydrating, marine fish drink masses of seawater and produce a trickle of concentrated urine.

When migrating fish like trout and salmon move into rivers and lakes, they face the opposite problem and risk absorbing too much water until eventually their cells begin to swell and burst. To avoid this, they switch from being heavy drinkers to plentiful urinators.

The amount of water intake depends on the type of water. Fish in saltwater or seawater have to drink and absorb more water in order to stay hydrated while fish in freshwater have to urinate more in order to prevent hyperhydration and maintain a balance of water inside their bodies.

As a fish drinks water or takes it into its skin, what happens is, water flows through its gills, where the exchange of gases takes place. In the gills, the water gives oxygen to the fish and takes the carbon dioxide released by its body. This is how a fish breathes through gills underwater.

Read More: can you drink alcohol while taking antibiotics

Do Saltwater Fish Drink Water?

Yes, all fish constantly drink water through their gills; this includes saltwater fish too. In fact, saltwater fish need to drink a lot more water than freshwater ones. This is because of the process of osmosis. Osmosis is a process by which a solvent moves from lower concentration to higher concentration through a selectively permeable membrane.

The water inside the body of a saltwater fish in the ocean has a low concentration of excess salt as compared to the water around their bodies (seawater or saltwater). Water flows from a less salty area to a saltier area. So the water flows from inside of the fish’s body to outside of it, that is, the sea, ocean or other saltier water bodies, through the membrane. This makes the ocean fish dehydrated, and to hydrate itself, the fish drinks more water.

The opposite case is with freshwater fish. Freshwater fish have a higher concentration of salt inside of their bodies and the river or the freshwater body has a lower concentration of salt. So the water flows inside the fish’s body through the permeable membrane and the fish gets swollen. To maintain the concentration of excess salt inside its body, a freshwater fish has to urinate more to get rid of excess water. As per science, the main reason behind saltwater fish drinking water constantly is to maintain a balance in the process of osmosis and to breathe. It may sound weird, but all fish drink water underwater and also pass urine underwater. This is why they instantly die when brought outside the water. They can’t breathe from the air.

Do All Sea Fish Drink Water?

The main reasons behind Earth being a habitable planet is that it has a definite type of atmospheric environment and that it has water. All organisms in this world need water to live. No water means no life. According to science, every organism needs water to survive, even if it lives underwater, especially so, actually. All fish drink water, no matter in which type of water they live. The type of water may affect the amount of water intake. A seawater fish needs to drink water more frequently than a fresh water one, and the reason behind this has already been explained.

There is an exception to this: sharks. Sharks are the opposite as they have very salty blood which makes the salt level of their body almost the same as the salt level of the water body (sea or ocean). So, sharks do not have a need to drink water to balance the process of osmosis. They do not have to get rid of excess salt or excess water from their bodies, because this is the natural state for them. They drink water only to breathe oxygen.

Restore Water Loss

Saltwater fish have a lower salt concentration inside their bodies than the saltwater they inhabit.

This results in osmosis, a process that removes water from their bodies and expels it into the sea.

This continuous and free diffusion of water through the gills shrivels up the fish. 

Maintain Optimal Fluid Balance

In a saltwater environment, fish experience more salt and less water around them.

As a result, their bodies take on salt and lose water to the sea.

Marine fish need to drink large quantities of water and urinate less to combat this problem.

In addition, their body absorbs only water and eliminates salt to maintain the required fluid balance.


Leave a Comment