Did Noah have to bring two of every sea creature on the ark? No, only the land animals were required. Sea creatures could survive in the water, but what about freshwater fish?

Well, first we have to understand that the preflood oceans probably weren’t as salty was today. The flood would’ve progressively dumped salt into the sea.

And we know that many freshwater and saltwater fish are part of the same kinds. This means there’s variety within a kind allowing certain kinds to adapt to freshwater or saltwater—something that likely happened after the flood. In other words, fish probably weren’t as specialized as they are today.