A: This is an excellent question.
Consider the following verses:
Genesis 6:17 - "And, behold, I, even I, do bring a flood
of waters upon the earth, to destroy all flesh, wherein
is the breath of life, from under heaven; and every
thing that is in the earth shall die."
Genesis 7:15 - "And they went in unto Noah into the ark,
two and two of all flesh, wherein is the breath of
life."
Two factors need to be considered. First, God destroyed
those creatures that have the "breath of life." This
would exempt those that breath through gills. Second,
God destroyed all flesh "upon the earth;" see also
Genesis 7:4 which states, "every living substance that I
have made will I destroy from off the face of the
earth." This refers specifically to land animals and not
to creatures that live in the waters. Therefore, even
creatures like whales that breath the breath of life
would be excluded because they do not live upon the
earth. Clearly, enough of these creatures would be able
to survive the flood so as to make their preservation in
the ark unnecessary.
Another way to consider it is to look at the kinds of
animals God made in the first chapter of Genesis and the
kinds that are taken on the ark. Five kinds of animals
are created: fish, fowl, beasts, cattle, and creeping
things. In Genesis 7:14, God lists the categories of
animals taken on the ark: "They, and every beast after
his kind, and all the cattle after their kind, and every
creeping thing that creepeth upon the earth after his
kind, and every fowl after his kind, every bird of every
sort." You will notice that four of the five categories
are mentioned with the fish being left out. They were
not included.
One final note: God classifies animals according to
habitat. He is not required to use our modern
classification system. In His classification system, a
fish is something that makes its major habitat in the
element of water. Therefore, whales are included as fish
(Genesis 1:21). We cannot take a classification system
designed about two hundred years ago by man and use it
to correct the biblical system written over three
thousand years ago. I hope this helps.
Till He comes,
David F. Reagan