Fish are strange specimens. There are fish which will
be killed in very short time if you add salt and change
the osmotic environment. However, there are other
fish which have the possibility to live in salt and fresh
water. This is very strange and there's also no sufficient
explanation how the fish are able to do that. You can put
a guppy from very smooth fresh water to hypersaline water
and he will not only survive but also still reproduce under
these conditions. To explain the difficulties of these changes:
A fish has a certain concentration of salts in its cells - like men.
If you let a fish swim in smooth water the cells will take up
water as osmotic effect. This has to be excreted as waste. In
salt water where the concentration of salts in the water is
higher than in the fish cells these will loose water and the
fish has to drink water to fill the cells. So the question is:
How can the fish change this system within minutes? Most
brackish water fishes can, but how?
Back to rainbows. They are relatively young freshwater fish
and also if they occur in smooth fresh water they can adapt
rather quickly to hard water (I don't know if they can adapt
to salt water I haven't tried it yet) and also to water with a
certain part of salt. Sea water is 35 g salt/liter, about five
teaspoon full (per liter!) and the salt addition for illness
treatment purposes is normally less. To my opinion the
unicellular offenders are not very adaptable to these changing
conditions if you add salt and thus dry out. However, I just know
salt works in many cases and don't really know why.
Does anybody know literature on this matter?
Please excuse me if you understand my English translation
only with the second reading but I'm not used to translate
this kind of stuff into English.
Harro