Fish must be very holy

[AFTT47]

Do you guys who all claim to want scientific proof of everything, look for it in anything? Salt water and fresh water does not readily mix.
http://oceanservice.noaa.gov/education/t...ation.html

The fresh water fish would live up top and the salt water would migrate lower. Where the two types of water met... Brackish water.

You could make a case that there isn't enough mixing in 40 days to cause a big enough salinity problem but you'll still have a temperature problem. The salt water layer would begin miles deep causing the temperature to plummet too low for most species to survive. All corals and all plant life (both aquatic and marine) would die. Of course all terrestrial plant life would die as well.