Genesis 7:23

And all the bodies of men and of beasts upon the face of the earth, from man to cattle, to creeping thing, and to the fowl which wingeth in the air of heaven, perished from the earth; and Noah only was left, and they who were with him in the ark.

AND HE BLOTTED OUT EVERY LIVING SUBSTANCE WHICH WAS UPON THE FACE OF THE EARTH. After having said, And all flesh perished, and having said, whatever was in the dry land, died, Scripture continues to say, And He blotted out, meaning that the bodies dissolved and became water, just as is in the verse, And he shall blot them out in the water of bitterness — for the waters of the flood were hot, as our Rabbis have said. But if so, the fish also would have died. Perhaps it was as the Rabbis have said in Bereshith Rabbah: “Whatever was in the dry land died, but not the fish in the sea. And some authorities say that they too were destined to be destroyed, but they fled to the Mediterranean.” (ocean), but usually meaning the Mediterranean Sea. (See Jastrow.) Either way the fish were saved.
Both of these opinions are plausible. For it is conceivable that the hot waters of the flood mingled with the seas, heating only their upper waters, while the fish descended to the depths of the ponds and lived there. Or, in accordance with the opinion of some authorities, it is possible that the fish in the waters of the countries near the Mediterranean (ocean), but usually meaning the Mediterranean Sea. (See Jastrow.) fled there when they felt the heat of the water, and were thus saved. And even if all those outside the Mediterranean died, since the majority of fish are in the Mediterranean (ocean), but usually meaning the Mediterranean Sea. (See Jastrow.) where the waters of the flood did not come down — as it is said, And the rain was upon the earth — the fish were thus saved. For none of the fish were brought into the ark to keep their seed alive, and at the time of the covenant it is said, I establish My covenant with you… and with every living creature that is with you, the fowl, and cattle, and every beast of the earth with you; of all that go out of the ark, but it does not mention the fish of the sea.

וימח את כל היקום, the structure of all the living beings was completely dissolved, but not that of the plants. “[trunks of trees might survive in recognisable form, whereas bodies would not be recognisable. Ed.]

This is why the Torah added the words מאדם ועד בהמה, עד רמש ועד עוף השמים וימחו מן הארץ, “man or beast, moving creatures, including the birds of the sky disintegrated completely.” No traceable remains survived.

וימח, the word is in the kal conjugation similar to וישע in Genesis 4,4, but it is in a transitive mode. There are verbs which by definition are in a transitive mode though they appear in the conjugation kal. [prominent examples are such roots as נתן, to give, רצח, to murder, etc. Ed.] וימחו מן הארץ, if G’d wiped out these creatures, וימח, is it not obvious that they were wiped out, וימחו? So what do these words tell us? The repetition is to indicate that they were so thoroughly wiped out that not a trace of them remained. [scientists digging for their remains would not find any. Ed.] There were no ruins left behind, concerning which anyone could ever say: “this building had been owned or built by a certain individual.” Our sages in Sanhedrin 108 understand the repetition asוימח referring to their destruction in this physical material world, whereas the word וימחו refers to their obliteration also from the world to come.

וישאר אך נח ואשר אתו בתבה, “there survived only Noach and the people and animals with him in the ark.” According to a quote attributed to Rabbi Yehudah hachasid, this wording contains a hint that the giant Og, later known as the king of Bashan, survived the deluge, the letters in the words: אך נח in our verse, which are unnecessary, have the same numerical value as the letters in the or עוג, (79)