Fish have evolved over millions of years to live within a certain range. The idea of keeping them out of range has been around for less than a couple decades. Darwin's theory says the last couple decades can go get stuffed, and not with good things like cheese and beer.
But really, the theory gained popularity not too long ago and generally a range of .019 to .020 is considered low salinity for this purpose. .008 is really low. The theory has also been debunked on numerous ocaisions. While the fish may seem fine for short term, they are in reality drowning slowly.
Fish, both saltwater and fresh maintain osmostic balance by adapting to the surrounding water. Saltwater fish take in a massive amount of water at any given time because their body is constantly trying to disolve and absorb the salt surrounding them. They do this by releasing water through their skin to disolve the salt. Freshwater fish maintain balance by taking in relatively little water. Put a fw
fish in salt and it dies by dehydration as it releases all of it's water to try and disolve the salt around it. Put a sw
fish in fresh and it drowns because it continues to pull in water, but not expel it through it's skin. Remember, this is happening at a cellular level and is nothing that can be controlled by the fish.
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