Why can't sharks live in fresh water?

Answer 1

The sharks body chemistry is designed to live in salt water. The concentration of salt on the inside of their cells matches the concentration of the water they live in. If you moved a shark to fresh water they would die.
Water will always move through a membrane (like skin or a cell membrane) in order to make the concentrations on both sides match. So, it the concentration is lower outside the shark water will be pulled in the sharks cells to try to dilute them. Problem is that too much water will break the cell open and kill them. This would cause the organs of the shark to stop working and the shark would swell up and die.

Answer 2

It is due to high salt level in their body that would disrupt the vital chemical processes if they will be in a less saline water.Though some sharks do live in freshwater but most are unable to reproduce in fresh water.
Recent research made in Lake Nicaragua has shed some light on the mystery of how some sharks can live in freshwater. It seems that sharks are able to reduce their bodily urea, sodium and chloride levels by excreting the excess salts via a rectal gland . This process makes them more adapted to freshwater but they still have a much higher salinity in their body than the surrounding water which means that the osmosis causes there body to absorb a large amount of water. It is believed that they sharks deals with this by extracting this water from their bodies by excretion urine. The massive amounts of water that are absorbed into their bodies by osmosis will result in that the shark produces up to 20 times more urine than they would in freshwater. Scientist believes that the kidneys regulate this water excretion which would but massive strain on them. It does however seem like the kidneys and the sharks doesn’t take damage from this extra strain since bull sharks has been documented to stay in freshwater for up to six years without negative effects to their health.

Answer 3

Some sharks can live in fresh water for a limited amount of time. Sharks have been known to swim up rivers such as the Mississippi, but only certain species of sharks have the ability.

Answer 4

What Sharks Live In Freshwater

Answer 5

Can Sharks Live In Freshwater

Answer 6

Bull sharks have been known to swim up rivers. They have a higher tolerance for fresh water than most other sharks.

Answer 7

Some can...Bull sharks have been found WAY upriver, and have been known to attack swimmers over 300 miles inland.

Don't know why salt-water fish can't live in fresh water, though...I can understand vice-versa, but you'd think salt-water fish would have no problem adapting to fresh.

Answer 8

Sharks have been living in salted water for ages, so they can not adapt to fresh water's life, because all of their organs are "working" because of salted water.It's something like putting diesel in a car which works with petrol!!!!

Answer 9

It might be because they have no bones

Vertebrate muscles require constant levels of calcium to operate. Ocen water is very hard, meaning it has lots of calcium. Some fresh water is also hard, but in areas of high rainfall, the water has very little calcium. Freshwater fish have internal skeletons of bone. This serves as a reservior if calcium levels in the blood fall. The bones of all vertebrates are constantly being dissolved and reformed to keep enough calcium present in the blood so the muscles can work properly.

Answer 10

In order to carry out the complex chemical reactions that sustain life, all living things—including sharks and people—have a supply of water and salts in their bodies. Although skin and other living tissue looks solid, it actually has tiny pores in it. Small molecules such as water and salts can pass readily back and forth through the skin. But if there is more of one kind of molecule on one side of the skin than on the other, some of the molecules will move from an area of higher concentration to an area of lower concentration, through a natural process called 'diffusion'. Diffusion will occur until the concentration of that molecule is equal on either side of the skin.

The sea is composed mostly water, but dissolved in the water are also various salts. The concentration of salts in seawater is usually about 3 to 4%. The living tissue of human beings and most fishes are considerably less salty than this. As a result, there is more fresh water inside the human or fish than outside in the sea. In response, water naturally diffuses from the body across the skin, as though attempting to dilute the outside sea. (The diffusion of water across a semi-permeable membrane is a special case of diffusion, usually termed 'osmosis'; in the interests of simplicity, I'll continue to use diffusion here.)

Human skin is relatively water-tight, but fish skin in rather leaky. As a result, the bodies of most marine fishes are constantly losing fresh water to the surrounding sea. But all living things need a supply of water inside their bodies in order to function properly. What most fishes must do to restore the water their bodies need is drink lots and lots of seawater You've heard the expression, "Drinks like a fish"? Well, it's true: marine fishes drink seawater almost constantly. In order to get rid of the excess salt contained in the seawater, many fishes have specialized salt-secreting structures in their gills called "chloride cells".

But sharks have hit upon a different strategy. Instead of being less salty than the sea, sharks store certain metabolic wastes (namely, urea and trimethylamine oxide, or TMAO for short) so that their overall 'saltiness' is actually slightly greater than that of the sea.

As a result, sharks do not continually lose their bodily supply of freshwater to the sea. Instead, any fresh water they need diffuses gently into their bodies through the mouth, gills, and other exposed membranes. Any excess water in a shark's body is filtered by the kidneys and excreted out an opening called the 'cloaca', located between the pelvic fins (the rearmost paired fins, behind the shark's belly). It's a very elegant solution to a significant environmental challenge. But it has its limitations.

If a typical sharks were to swim its very 'salty' body into fresh water, so much fresh water would diffuse into its tissues that the kidneys would have to work overtime in order to get rid of it all. This is a very energy-demanding process, and explains WHY most sharks do NOT enter fresh water: it's simply too much effort to keep excreting all that freshwater. But some sharks, such as the Bull Shark (Carcharhinus leucas), are able to enter fresh water for prolonged periods. They achieve this neat trick by greatly reducing their bodily concentrations of urea and TMAO. Even so, a Bull Shark in fresh water is slightly saltier than its surrounding environment, so that it must continually excrete excess water in the form of dilute urine. In total, some 43 species of sharks and rays (which are essentially flattened sharks) spend at least part of their lives in fresh water.