And God said,
Let the waters bring forth abundantly the moving creature that has life, and fowl that may fly above the earth in the open firmament of heaven.
All Commentaries on Genesis 1:20 Go To Genesis 1
Basil the Great
After the creation of the luminaries the waters are now filled with living beings and its own adornment is given to this part of the world. Earth had received hers from her own plants, the heavens had received the flowers of the stars, and, like two eyes, the great luminaries beautified them in concert. It still remained for the waters to receive their adornment. The command was given, and immediately the rivers and lakes becoming fruitful brought forth their natural broods; the sea travailed with all kinds of swimming creatures; not even in mud and marshes did the water remain idle; it took its part in creation. Everywhere from its ebullition frogs, gnats and flies came forth. For that which we see today is the sign of the past. Thus everywhere the water hastened to obey the Creator's command. Who could count the species which the great and ineffable power of God caused to be suddenly seen living and moving, when this command had empowered the waters to bring forth life? Let the waters bring forth moving creatures that have life. Then for the first time is made a being with life and feeling. For though plants and trees be said to live, seeing that they share the power of being nourished and growing; nevertheless they are neither living beings, nor have they life. To create these last God said, Let the water produce moving creatures.
Every creature that swims, whether it skims on the surface of the waters, or cleaves the depths, is of the nature of a moving creature, since it drags itself on the body of the water. Certain aquatic animals have feet and walk; especially amphibia, such as seals, crabs, crocodiles, river horses and frogs; but they are above all gifted with the power of swimming. Thus it is said, Let the waters produce moving creatures. In these few words what species is omitted? Which is not included in the command of the Creator? Do we not see viviparous animals, seals, dolphins, rays and all cartilaginous animals? Do we not see oviparous animals comprising every sort of fish, those which have a skin and those which have scales, those which have fins and those which have not? This command has only required one word, even less than a word, a sign, a motion of the divine will, and it has such a wide sense that it includes all the varieties and all the families of fish. To review them all would be to undertake to count the waves of the ocean or to measure its waters in the hollow of the hand. Let the waters produce moving creatures. That is to say, those which people the high seas and those which love the shores; those which inhabit the depths and those which attach themselves to rocks; those which are gregarious and those which live dispersed, the cetaceous, the huge, and the tiny. It is from the same power, the same command, that all, small and great receive their existence. Let the waters bring forth. These words show you the natural affinity of animals which swim in the water; thus, fish, when drawn out of the water, quickly die, because they have no respiration such as could attract our air and water is their element, as air is that of terrestrial animals. The reason for it is clear. With us the lung, that porous and spongy portion of the inward parts which receives air by the dilatation of the chest, disperses and cools interior warmth; in fish the motion of the gills, which open and shut by turns to take in and to eject the water, takes the place of respiration. Fish have a peculiar lot, a special nature, a nourishment of their own, a life apart. Thus they cannot be tamed and cannot bear the touch of a man's hand.