There would be no fish if there had been a global flood.
Small changes in water condition kills fish. As anyone that has purchased fish for a tank know, you need to slowly add fish to a new tank so they get accustomed to the new conditions.
Further, flooding causes fresh water fish to die, as in Australia recently.http://www.abc.net.au/news/2010-12-13/thousands-of-fish-die-in-floodwaters/2372224
Fish researcher Bill Sawynok says they appear to have died in a natural process that occurs during flooding.
"With the rising flood waters, it's inundated the vegetation which after a few days starts to rot," he said.
"That actually takes the oxygen out of the water and therefore the fish basically don't have any oxygen to breathe."
Finally, as the fresh water lakes and salt water oceans merged together, the dilute mixuture of brine would have killed any remaining fish of both salt or fresh water varieties.