So there is a disease on aquarium fish called the white spot disease (sometime called Ich disease). It make fish to die very quickly. One way to treat that disease is to add salt to the fish tank. Something like 1 table spoon per gallons. Now I have done this many times to treat fish disease and it very effective. But one thing I don’t understand is that. Given that all my fish are fresh water fish, how come they can still survive just fine in salt water?. Like for months already
In: Biology
The very short answer is that most freshwater fish have a general tolerance for certain levels of salt, above the tolerance that ichthyophthirius multifiliis, the parasite that causes ich, has.
Even tiny concentrations of salt will kill off the parasite, but a little bit is ok. Fish broadly have a mucus lining that protects them from environmental contamination (like salt) to a certain degree.
In the same way an antibiotic will cure a bacterial infection but leave you mostly ok. Your body just has a higher tolerance for it than the bacteria does. Now, too much salt will absolutely kill your fish, just like too much of anything will kill anything.
But a little bit of salt isn’t going to kill most fresh water fish. There’s natural salts in riverbeds and floors that gets stirred up into naturally flowing water all the time. So most of your freshwater fish will be fine with a little bit of it.
it just happens to be *really* good at killing ich, and the toxic threshold for ich is below the toxic threshold for most fish.
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