Leupold Genesis part 51 verse 20

20. And God said: Let the waters swarm with swarms of living souls, and let birds fly above the ground across the face of the firmament of the heavens.

The work of the fifth day is also in a sense a double one, but its double character is by no means as pronounced as that of the third and the sixth days. For to have the waters and the skies filled with such creatures as these parts are best adapted to is in reality a work whose two parts are practically identical in nature. However, here the situation is not analogous to the work of the third day, where "the earth brought forth." Here it is not the waters that bring forth. A. V. is in error when it translates: "Let the waters bring forth abundantly." Luther did not make this mistake. The optative of the verb sharats followed by the cognate object shaerets here must mean: "Let the waters swarm with swarms." Meek is more idiomatic: "Let the waters teem with shoals," but he loses the cognate object. We simply do not know from what source fish and birds sprang. They are simply bidden to people their respective domains. In apposition with the cognate object sherets stands the expression, "living souls" or literally, "souls of life." The word "soul" (nephesh) is here used for the first time--a collective singular--as a designation of these aquatic creatures, because the soul is the most important part of them, and at the same time the term definitely points to the new and distinctive thing involved. This is the first time that life in souls or living souls appears. According to the Biblical viewpoint plants have no life. But the life of living creatures is present in their "souls," and so they have souls ascribed to them. But this "soul" again is regarded as nothing more than "that which breathes" (B D B) in any being. A kindred form of life to that of fish is that of birds. Each type has its special element. The polel form ye'opkepk is intensive and so implies: birds shall "fly back and forth." Their element is described as being "above the ground across the face of the firmament of the heavens." The firmament is regarded as having a face, that is a side turned toward and, as we say, "facing" the earth. Across this the birds are to disport themselves. Sherets used in reference to the fish is a graphically descriptive term. All forms of life that love to move in continual agitation through one another, like shoals of fish and the like, are involved. This pronounced gregarious instinct marks these creatures to this day. By this work the emptiness (bohu) of the heavens and the waters is cancelled.