The fifth day of creation brings into existence water creatures and birds.

And God said: see Gen 1.3 and Gen 1.6.

Let the waters bring forth swarms of living creatures: this is literally “Let the waters swarm with swarming beings,” in which “being” translates Hebrew nefesh, a term most often applied in the Old Testament to human beings. Living creatures in this context refers to all forms of life that live in the water. Swarms translates a term also used in Exo 8.3, which speaks of the Nile swarming with frogs. A “swarm” describes a mass of moving living objects on land, in water, or in the air. Here the swarming is in the water. See also Gen 7.21. The command is addressed to the waters as the place where the living creatures are to swarm. This command may have to be translated “be filled,” as in Good News Translation. For example, “the waters must now be filled with living creatures,” or as a direct command, “Waters, swarm with masses of living beings.”

It may be necessary to express living creatures as, for example, “all kinds of sea animals,” “every kind of fish and animal that lives in the water,” or “everything that swims or moves in the water.” Languages differ greatly in what is included in such a description, and so translators should try to be as general as possible but avoid an expression that includes water fowl, if possible. In some languages the general term for “fish” refers to all kinds of creatures in the sea, and so “all different kinds of fish” will be quite appropriate here.

And let birds fly … is the second command. This is not a command for birds that exist to fly, but a command bringing birds into existence. A literal translation of and let birds fly may say that the birds already exist and are now being turned loose to fly. If this is the case it may be necessary to say, for example, “Let birds be created and fly,” “And now birds must appear and fly,” or “Birds, appear and fly.” Birds translates a noun related to the verb “to fly,” and some interpreters take the word in a general sense to mean “flying creatures,” which includes flying insects and bats. However, the verb also has the sense of “fly to and fro,” which seems to apply more particularly to birds alone. Nearly all modern translations use a word restricted to flying fowls or birds with wings, and this is recommended to translators.

Above the earth and across the firmament of the heavens express things from the viewpoint of a human being. The birds are to fly in the air or in the space between the sky and the earth.

Languages differ greatly in the way they classify animals and birds. A term that includes birds that fly may also include flying insects and bats as well. In some languages a general term for birds may include only large birds of prey, particularly in the context of “fly above the earth.” In such cases it may be necessary to mention more than one class of birds in order to include most birds that fly.

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .