Nonsense of Noah
Fish, even though they live in water, would not have survived the Flood
The seemingly immune marine life could have fared no better than their terrestrial counterparts because, first of all, the rapid mixture of salt and fresh water from the conglomeration of various pure water sources would have killed all known marine creatures in a matter of hours. End of story.
Of course, that is not really the end of the story. Like terrestrial creatures, some marine species have very specific requirements for their habitats. One such example would be the delicate breeding ground for salmon. The violent floodwaters would have certainly eradicated these fragile aspects of their environment. Similarly, the force of the rainfall would instigate an integration of large mud deposits with the now semi-salty water. This scenario would undoubtedly create an increasingly lethal environment for marine life requiring crystal clear water.
The required five-mile rise in the global water level would have drastically altered the pressure exerted within the ocean and forced many species to leave their only hospitable levels in order to avoid a pressure-inducing death by implosion. You may also recall that the oceans should already be boiling from subterranean lava, outer space asteroids, torrential raindrop impacts, and whatever else might be necessary to maintain apologetic proposals. Remarkably, we could consider salt and mud to be the least of the threats against aquatic survival.