What happens if you put a shark in fresh water?

Question

The question arose when my 3 year old son asked why there weren't any sharks in the lake we were visiting. We told him sharks don't live in fresh water. When he asked why, We wondered what would happen if you put an open ocean shark in a fresh water lake.

I am sure their gills are designed and optimized for salt water, so I suspect they'd die, but I wonder how long they'd live and how horrible the death would be.

Answer 1

Big oopsie! There ARE freshwater sharks, even though the sharks have the ability to survive better in salt water. Lake Nicaragua is the place to see them. Occasionally, sharks will swim up rivers, if the food is there. The high concentration of salt is excreted through the digitiform gland, toward the end of the digestive tract.

You just raised an interesting research topic. Do the FW sharks from L. Nicaragua have smaller digitiform glands than the other sharks? Or do they just use them less? For the right research grant, I'd be happy to find out.

Answer 2

http://www.amonline.net.au/fishes/fishfa...

The Bull Shark can live in a wide range of habitats from coastal marine and estuarine, to freshwater. It has been recorded from the surf zone down to a depth of at least 150 m. It is the only species of shark that is known to stay for extended periods in freshwater. It has been reported nearly 4000 km from the sea in the Amazon River system, and is known to breed in Lake Nicaragua, Central America.

http://en.wikipedia.org/wiki/Bull_shark#...

Only 43 species of elasmobranch in ten genera and four families have been reported to enter fresh water, of which the bull shark is the best known. Other species that enter rivers include the stingrays (Dasyatidae, Potamotygonidae and others) and sawfishes (Pristidae). Some skates (Rajidae), smooth dogfishes (Triakidae), and sandbar sharks (Carcharhinus plumbeus) regularly enter estuaries. The ability of elasmobranchs to enter fresh water is limited because their blood is normally at least as salty (in terms of osmotic strength) as seawater, through the accumulation of urea and trimethylamine oxide, but bull sharks living in fresh water reduce the concentration of these solutes by up to 50%. Even so, bull sharks living in fresh water need to produce twenty times more urine than those in salt water.

Until the 1970s, researchers thought the sharks in Lake Nicaragua were a separate species because there was no way for the sharks to move in or out. It was discovered that they were jumping along the rapids just like salmon. Bull sharks tagged inside the lake were later caught in the open ocean.

http://www.elasmo-research.org/education...

....and the notorious Bull Shark (Carcharhinus leucas), all of which penetrate far up freshwater rivers — the Bull Shark has been recorded some 2,600 miles (4,200 kilometres) from the mouth of the Amazon River — and some even complete their life cycles in freshwater.

Answer 3

Actually, some sharks can live in fresh water. The bullshark and the tiger shark can both live in fresh water for a period of time. The question with these sharks would be if there was enough food to sustain life.

Answer 4

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. Diffusion is the same process that allows a sugar cube to completely dissolve in a cup of tea or coffee: the sugar molecules spread out from an area of high concentration (the cube) to an area of low concentration (the tea or coffee); eventually, all parts of the tea or coffee are equally sugary.

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. But one family of South American stingrays — the so-called River Stingrays (Potamotrygonidae) — evolved from a marine ancestor to become thoroughly adapted to living in fresh water. So much so, in fact, that their bodies have lost the ability to manufacture urea and — if placed in full-strength seawater, they quickly die. These freshwater stingrays are thus trapped by their biochemistry.

Sometimes, you can't go home again.

Answer 5

They would live in fresh water for about 30 minutes and they die.Their death are not that horrible because the shark would sink and then blood comes out.The bull shark and the tiger shark are the only sharks that can live in fresh water rivers for a longer period of time.They only live in fresh waet which are connected to the ocean