fresh in marine

[h1n1]

simple question, why cannot fresh water fish survive in marine waters? and visa vera?

 

[Soggy]

Among other things, because of the way their bodies process the salt. The body of freshwater fish is designed to retain salt because of the scarcity in it's environment, The body of a saltwater fish is designed to discard it. some fish like salmon which transit between fresh and salt during their lives can deal with both.

 

[h1n1]

ohh thanks that explains it sorta, bc how does retaining salt have to do with killing them?

 

[andyjs]

Even species that can survive in both need to transition between them fairly slowly. The differences in osmotic pressures can destroy the fish's cells causing them to die

 

[pk705]

It all has to do with osmotic pressure - different salt concentrations pull water in/out of tissue, resulting in cells either expanding (eventually rupturing) or contracting to the point where they cannot function normally; for a more detailed explanation, google Osmosis.