Salmon lead remarkable lives. Born in freshwater streams, they make an epic journey downstream to the ocean as juveniles. After years roaming the salty seas, the salmon return to their natal streams to spawn and die. This life cycle requires the salmon to transition between radically different environments – from fresh to saltwater and back again. A key challenge they face is maintaining proper water and ion balance, or osmoregulation, despite living in fresh and saltwater. So, do salmon drink water? And how do they survive in both fresh and salty environments? Let’s take a deep dive into the osmoregulation of salmon.
The Osmoregulatory Challenges Salmon Face
To understand salmon osmoregulation, we first need to grasp the contrasting environments salmon inhabit. Freshwater contains limited dissolved salts and minerals Yet inside a salmon’s body, salts like sodium and chloride are critical for normal cell function. This means in freshwater, salmon face the threat of losing salts to their dilute surroundings Saltwater has the opposite problem – it’s packed with salts and minerals. When salmon swim in the ocean, water will diffuse into their bodies while excess salts diffuse inside. Without adaptations, salmon would either dry out or get overloaded with salts.
Osmoregulation allows salmon to maintain proper water and salt balance despite their ever-changing surroundings. Let’s look at how adult salmon deal with saltwater first.
How Salmon Survive in the Salty Sea
The ocean poses a major osmoregulatory challenge for salmon. Seawater contains over 3% dissolved salts versus just 1% inside a salmon’s body. The huge salt imbalance causes salmon to constantly lose water to their environment through osmosis. Salmon counteract this by drinking large amounts of seawater. They also excrete a highly concentrated urine to rid excess salts. Specialized chloride cells in their gills pump sodium, chloride and other ions out to counteract diffusion of salts into the body. Together, these adaptations allow salmon to thrive in saltwater that would kill most freshwater fish.
The Transition From Freshwater to Saltwater
Salmon don’t transform into saltwater-tolerant fish overnight. When migrating downstream as juveniles, salmon undergo dramatic physiological changes to acclimate to saltwater. This process begins when they reach the brackish water where fresh and saltwater mix near river mouths. Here salmon remain for days or even weeks as their bodies adjust. During this time, salmon begin drinking seawater and their kidneys start excreting a concentrated urine. Chloride cells in their gills also shift into reverse, now actively pumping salts out rather than in. Only once fully acclimated will the salmon swim out to sea.
How Adult Salmon Return to Freshwater to Spawn
After several years in the ocean salmon face another osmoregulatory challenge as adults. To spawn they must migrate back up their natal freshwater streams. Suddenly the salts salmon worked so hard to retain in the ocean now threaten to overload their bodies. So how do salmon re-acclimate to freshwater? First, they cease drinking when they reach the estuary, relying on water absorbed through their food. Their kidneys switch to producing large volumes of dilute urine to flush out excess salts. And the chloride cells in their gills reverse yet again, now pumping salts from the dilute stream water into their blood to counter diffusion.
Through their amazing physiological adaptations, salmon can migrate between two drastically different worlds – the salty sea and their freshwater birthplace. Their ability to osmoregulate in both environments enables an incredible life cycle that spans continents. After spawning, the salmon’s epic life ends where it began. Their decaying bodies infuse the stream with nutrients that nourish the next generation of salmon fry. Though short-lived as individuals, salmon live on through their offspring and the timeless cycle of migration between land and sea.
Can People and Animals Drink Seawater?
Marine animals, like sea otters, have efficient kidneys that help flush out salt from the seawater 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. In freshwater, salmon pump sodium in, but once they enter the ocean, they begin pumping out sodium and chloride ions extracted from ocean salt that enters their bodies.
How Do Salmon Adapt To Fresh And Saltwater? – The Marine Life Explorer
FAQ
Can fish drink water?
Yes, fish drink water, but not in the same way humans do. Freshwater and saltwater fish have different needs and methods for regulating water and salt in their bodies.
Are there any animals that don’t drink water?
Yes, certain animals can survive without ever directly drinking water. Kangaroo rats, for example, are known to survive solely on the water derived from the seeds they eat, and their bodies are highly efficient at conserving water.
Are salmon freshwater or saltwater?
Salmon are both freshwater and saltwater fish. Most salmon species are anadromous, meaning they live in the ocean (saltwater) but migrate to freshwater rivers to spawn.
How much water is in salmon?
Raw wild salmon is 70% water, 20% protein, 6% fat, and contains no carbohydrates (table). In a 100 gram reference amount, raw salmon supplies 142 calories, and is a rich source (20% or more of the Daily Value, DV) of several B vitamins, especially vitamin B12 at 133% DV, selenium (52% DV), and phosphorus (29% DV).
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 do salmon hydrate?
Behaviorally salmon will prevent over hydration (in freshwater) by drinking less or no water, and having diluted urine (more water than salt). In saltwater they do the opposite, they will hydrate by drinking water and they will have concentrated urine (more salt than water).
How much water does a salmon drink a day?
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). You’re probably thinking “It’s a fish surrounded by water.. of course it drinks”!
Can salmon move from fresh water to salt water?
The behavioral (drinking or not drinking) and physiological changes a salmon must make when moving from fresh water to salt water — and vice versa — are essential, but cannot be accomplished immediately.
What happens if a salmon eats fresh water?
In sum, a salmon in the ocean is faced with the simultaneous problems of dehydration (much like a terrestrial animal, such as yourself) and salt loading. However, if fresh water, the problem is basically reversed. Here, the salmon is bathed in a medium that is nearly devoid of ions, especially NaCl, and much more dilute than its body fluids.
How does saltwater affect salmon hydration?
When talking about saltwater or freshwater, water will move through the semipermeable membrane to the side that has a higher salt concentration. This means that salmon in freshwater have to have an adaptation to prevent over hydration, and in saltwater they need an adaptation to prevent dehydration.