Why can't fish that live in rivers live in the sea or the the othe way round .?

Question

to shawntae why did you bother to answer this question.did you need the 2 points that much

Answer 1

This is simple. A freshwater fish has organs designed to stand fresh water. If a freshwater fish was put in salt water, which has a higher pressure, its internal organs would collapse, it would die from lower oxygen levels, and there insides don't have a proper coating to stand the salt.

Its the same for saltwater fish in freshwater. Freshwater is less dense, and there organs would "explode". Also, freshwater has more bacteria than saltwater, so they would die from diseases not found in the ocean.

Both kinds of fish have an organ that keeps their buoyancy in check. They are specifically disigned for the water they live in. Freshwater fish would sink in saltwater, and saltwater fish would stay at the surface uncontrollably in fresh water.

This applies for all fish exept migrating fish like trout and salmon, as well as a few sharks.

Answer 2

This has to do with osmoregulation, or the amount of ions in the water (all soluble salts dissociate into their ions when put into water). Many of these ions (Na, Ca, K, Cl) are needed by fish for their life processes. In freshwater fish, the water contains less ions than the body of the fish, so they have specialized chloride cells to bring the ions into their bodies and keep them there. This requires the expenditure of a lot of energy on the part of the fish. In saltwater fish, there are more ions than the fish need, so they use the same chloride cells to expel excess ions from their bodies. Again, this takes a lot of the fish's energy.

Most fish are adapted to one environment or another. If a freshwater fish gains some salt in their water (or a saltwater fish is in a tank with slightly less salt), it can benefit the fish from having to use less energy to obtain/expel ions. But once a certain point is passed, the fish can't efficiently expel unnecessary salt or gain enough. These fish will die. Some can function efficiently in both environments and are able to cross back and forth between each.

Answer 3

It doesn't matter which way round they are they still can't do what you said.

It's all to do with the earths gravitational pull & the FTSE index
fish that live in rivers don't like salt and fish that live in the sea don't like fishermen with large nets or wooly jumpers its all to do with breeding, from an early age fish realise that they cannot live without the salt water unlike the fresh water variety
thats why you never hear a fish say "can you pass the salt" or "I ordered mushy peas with this"

Answer 4

Some river fish can live in salt water,but other's can't as their gills can't deal with the salt.

Sea fish have the other problem-their gills can't process water without salt.

Answer 5

Fresh water creates a hypotonic environment for aquatic organisms. This is problematic for some organisms, whose cell walls will burst if excess water is not excreted. Some protists accomplish this using contractile vacuoles while freshwater fishes excrete excess water via the kidney. Although most aquatic organisms have a limited ability to regulate their osmotic balance and therefore can only live within a narrow range of salinity, some fishes have the ability to migrate between fresh water and sea water.

As with many aquatic animals, most fishes release their nitrogenous wastes as ammonia. Some of the wastes diffuse through the gills into the surrounding water. Others are removed by the kidneys, excretory organs that filter wastes from the blood. Kidneys help fishes control the amount of ammonia in their bodies. Saltwater fish tend to lose water because of osmosis. In saltwater fish, the kidneys concentrate wastes and return as much water as possible back to the body. The reverse happens in freshwater fish, they tend to gain water continuously. The kidneys of freshwater fish are specially adapted to pump out large amounts of dilute urine. Some fishes have specially adapted kidneys that change their function, allowing them to move from freshwater to saltwater

this is a process that eveolution took care of years ago. There are a number of fish that can live in fresh, brackish and salt. Trout is not one of them. A form of trout known as a steelhead can and does along with Salmon, black mollies and guppies. Some smaller shark species can as well.

Hope this helps.

Answer 6

lets see, your betta, it really is the hardest fish you should purchase, and the champion of small tank survival, died. This tells you something about the tank... If a betta can't stay in it, NO different fish will live to inform the tale. Ian

Answer 7

Some do.

Many fish travel into rivers (famously, salmon) for breeding, and travel thousands of miles in the ocean at other times.

Some species are salt-sensitive (it can be toxic, affect the permeability of membranes, or alter buoyancy), so that they either function (or survive) better with it, or without it. Sometimes it is their food-source that needs the salt, or cannot tolerate it.

Answer 8

freshwater is different than saltwater. some fish can survive in a mix of both, like where a river meets the sea.

Answer 9

some fish can. salmon and eels for example. but to answer your question its down to being adapted to the salt in the water. some fish need the salt and some need fresh water and then theres our friends the eels that can handle either. its like some animals need heat and some need cold. just the way they made i guess

Answer 10

Fresh water fish aren't capable of tolerating the salt.It builds up on there gills and causes them to drown.