As anadromous as they are, salmon hatch their fragile young in safe freshwater lakes and streams and then move to saltwater. They spend their adult lives in the ocean before swimming back to where they began their lives. Like salmon, striped bass and sea lamprey also spawn in freshwater and mature in saltwater. Catadromous fish, like eels, go the other way; they lay their eggs in the ocean and then move to fresh water. This migration is made possible by a biological process called osmoregulation.
Osmoregulation is the way salmon control bodily fluids as they move between freshwater and saltwater. The process begins during the smolt phase, when juvenile salmon prepare themselves to swim out to sea.
The first thing that happens is a smolt begins taking in a lot of water. Next, its kidneys stop producing as much urine. Finally, a molecular pump in the salmon’s gills switches direction. Instead of capturing sodium from the freshwater, it begins pumping sodium out. When an adult fish swims back to its spawning grounds in fresh water, the changes happen again. The fish spends a few days in areas where freshwater and saltwater meet.
Salmon can swim both in and out of water. They are born in freshwater, move to the ocean, and then come back to freshwater to spawn. For this amazing life cycle to work, salmon have to move between two very different types of water. One important question is how salmon deal with changing salt levels and stay hydrated as they move from freshwater to saltwater. Specifically, do salmon even drink water like terrestrial animals?.
Do Salmon Drink in Freshwater?
When living in rivers and lakes, young salmon do ingest fresh water but they limit their intake. Freshwater contains little salt, so salmon are at risk of taking on excess water and having their cells rupture.
To keep from getting too thirsty, salmon rely more on the nutrients in their food and make very watery urine to get rid of extra water. Their kidneys change so that their urine has less salt than the rest of their body fluids.
So in freshwater, salmon minimize drinking and have urine with low salt content relative to their body. This prevents too much water from flooding into their cells.
Do Salmon Drink in Saltwater?
In contrast, salmon increase their water intake when living in the ocean Seawater has high salt content, so salmon are at risk of dehydration as water passively leaves their bodies to balance concentrations
To stay hydrated in their salty environment, salmon actively drink seawater. Their kidneys then work to expel the excess salts through concentrated urine. When compared to their body fluids, ocean urine has more salts like sodium and chloride in it.
Drinking more while producing salty urine allows salmon to maintain hydration without their cells taking on dangerously high salt levels.
How Do Salmon Survive Drinking Saltwater?
An important question is how salmon avoid toxicity from drinking seawater which has about 3 times more salt than their body fluids.
The answer lies in a specialized enzyme called Na+/K+-ATPase found in their gill cells. This enzyme functions as a molecular pump by using ATP to move sodium ions out of the body into the surrounding water. This mechanism allows salmon to ingest saltwater to stay hydrated but then expel the excess sodium and chloride before it can build up to toxic levels.
So salmon rely on this enzyme to “desalt” the seawater they drink by actively pumping salt out through their gills. The sodium-potassium pump allows them to drink and obtain water while avoiding salt overload.
Osmoregulation Between Environments
The ability to adapt between freshwater and saltwater by regulating hydration and salt levels is known as osmoregulation. Salmon undergo dramatic physiological changes during their migration to adjust to living in both types of habitat:
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In freshwater, they reduce drinking and excrete dilute urine to avoid taking on too much water.
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In saltwater, they drink and have concentrated urine to hydrate while expelling salts.
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Enzymes in their gills pump salt out of blood to avoid toxicity from saltwater ingestion.
Through osmoregulation, salmon can thrive in both low salt freshwater and high salt marine environments during their complex life cycle.
Behavioral Adaptations for Osmoregulation
In addition to their physiology, salmon display behaviors that help them maintain fluid and salt balance:
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As smolts transitioning to the ocean, they will wait for optimal health and conditions before migrating.
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In freshwater, salmon may school to deeper parts of lakes and rivers to avoid warm surface water that increases osmotic stress.
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Salmon migrating upriver will stop in estuaries to gradually adjust their osmoregulation for freshwater.
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Spawning salmon reduce or stop feeding as they enter freshwater, relying on fat stores and reducing fluid intake.
These behaviors complement the physiological changes and help salmon successfully regulate fluids throughout their life stages.
Importance for Survival and Reproduction
The ability to osmoregulate enables salmon to undertake their iconic migrations between freshwater and marine environments. Without being able to adapt to dramatic salt level changes, salmon would be unable to complete their life cycle.
Osmoregulation allows salmon to:
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Survive the transition from streams to the ocean as juveniles.
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Feed and mature for years in the productive marine environment.
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Return to freshwater rivers and lakes to continue the cycle through spawning.
So the capacity to regulate hydration and salt balance through physiological and behavioral adaptations is critical for the success, reproduction, and perpetuation of wild salmon populations.
Can People and Animals Drink Seawater?
Animals that live in the ocean, like sea otters, have kidneys that work well and help flush out salt from the water they live in. U. S. Fish and Wildlife Service.
If salmon can survive in saltwater, why can’t human beings and other animals do it too? Most animals are only adapted to live either in freshwater or saltwater. Humans can’t produce urine that’s saltier than blood, and ocean water has three times more salt than our blood. Our kidneys can’t filter out the salt in seawater, and we become dehydrated over time.
Some marine animals, known as osmoconformers, don’t drink water the same way we do. Instead, invertebrates like shrimp and jellyfish take water in through their skin, filtering out the salt as they do. Like salmon, saltwater fish have efficient kidneys that can remove excess salt through urine, gills, and skin. Seabirds have efficient kidneys, as well as special glands to manage saltwater. The birds can dribble salty water out of their beaks. The kidneys of marine mammals, such as sea lions and whales, are also especially adapted for flushing out seawater. The urine of those animals can be up to 2.5 times more salty than seawater.
How Do We Know About Osmoregulation?
In 1957, a Danish chemist named Jens C. Skou discovered that animal cells that control nerve impulses, muscle contractions, and digestion require more potassium inside the cell than outside it. Likewise, the cell needs more sodium ions outside the cell than inside it. Skou discovered an enzyme in our cells called Nz+/K+_ATPase — or NKA for short — which acts as a pump to transport these sodium ions in and out of cell walls. Many cells spend a fifth of its energy on these pumps; nerve cells spend 2/3rds of their energy moving around sodium ions. For his research, Skou won the Nobel Prize in Chemistry in 1997.
Salmon use NKA pumps to move sodium in the right direction. When salmon are in fresh water, they take in sodium. But when they get to the ocean, they start to release sodium and chloride ions that they get from the salt in the water.
Do Fish Drink Water?
FAQ
What do salmon drink?
Does salmon absorb water?
Do fish drink water or just breathe it?
How do salmon change from saltwater to freshwater?
Does a salmon drink water?
You’re probably thinking “It’s a fish surrounded by water, so of course it drinks!”, but in fresh water (where water loading is the problem) the salmon doesn’t drink at all. The only water it consumes is that which necessarily goes down its gullet when it feeds.
Is wild salmon healthy?
Wild salmon is considered healthy, since it provides proteins, vitamins, minerals and unsaturated fats such as omega 3, which help in maintenance of cardiovascular health. Although it has a considerably higher caloric value than other fish, its calories are exceptionally nutritious, since the fish is high in protein and healthy fat.
Do salmon eat salt water?
Fortunately, the salmon has some remarkable adaptations, both behavioral and physiological, that allow it to thrive in both fresh and salt water habitats. To offset the dehydrating effects of salt water, the salmon drinks copiously (several liters per day).
How much water does salmon drink a day?
To offset the dehydrating effects of salt water, the salmon drinks copiously (several liters per day). You’re probably thinking “It’s a fish surrounded by water, so of course it drinks!”, but in fresh water (where water loading is the problem) the salmon doesn’t drink at all.