As for whether the original ocean was salty or fresh, the thing is that there are forms of marine life that can only live in the one, or the other due (among other things) to the problem of osmoregulation.
Apparently you have not read enough about adaptation.
I have read quite a lot about it. What adaptation would be required for an animal adapted exclusively to living in salt water to move to fresh, or vice versa? Consider in your answer the structural differences between salt-adapted vs fresh-adapted creatures. How would that be achieved , in the timescale of the Great Flood? If the animals have existed unchanged since Creation, how is this adaptation achieved? And if they are changed since Creation, isn't that evolution?.
The animals alive at the time of the Flood were only about 1,700 years away from near perfection. They had a tenth of the mutations animals have now. The animals alive today are about 4,500 years since the Flood. Much of their adaptability has been lost.
Since you are locked into the present you don't seem to be able to conceive things have not always been the way they are now. Therefore I will not respond further.
Oh I see. What you are saying is that species today are different from those in existence at the time of the Creation. They have adapted, as you say. You say that this has occurred by way of mutations, changing them over time over time, from what they originally were to what they are now.
In other words, what you are saying is that they've evolved.
