[smokingfrog]

Beats me. I guess there are slight differences in the 100 genetically distinct populations of fish that allow some to survive in warmer waters.

[Ramius]

Or maybe... there’s no difference at all.

[Bernard Marx]

I guess there are slight differences in the 100 genetically distinct populations of fish that allow some to survive in warmer waters.

Which is why various life forms have been able to adapt to and survive thousands of climate variations over the past few million years. Natural selection.