Not all organisms survived the flood and we know for a fact many groups went extinct that is why we have a fossil record.
But, how could all those salt water fish be alive today if they went exitinct at the time of the global flood, which according to creationists, was just 4000 years ago.
Not every sea creature or fish went extinct. We have some fish that can survive both fresh and salt water.
God did not go in to dtail on how he did everything and it left us speculating as we gain knowledge.
That is obvious conjecture on your part. You place yourself in irresolvable contradictions when you make up nonsense as you go along.