And God blessed them, and God said unto them, Be fruitful, and multiply, and replenish the earth, and subdue it: and have dominion over the fish of the sea, and over the fowl of the air, and over every living thing that moveth upon the earth. Genesis 1:28
"The imaginary process of transforming fish fins into human legs would
leave the in-between creature either unable to swim or unable to walk.
Take enough of a fish’s fins away on its supposed journey to land life,
and it loses its ability to track down dinner before it becomes dinner." ICR