[Physicist]

Why would a fish be adapted for movement on the surface?

The current thinking is that the proto-amphibians adapted fins into limbs because it enabled them to wriggle through dense aquatic vegetation more easily. That the limbs enabled them to move clumsily about on land was fortuitous.

[PatrickHenry]

The current thinking is that the proto-amphibians adapted fins into limbs because it enabled them to wriggle through dense aquatic vegetation more easily.

And we still have "walking catfish" moving about on land. Walking catfish .