"blessed the animals that he had made"
Be fruitful and multiply
This is God's blessing. He told the sea animals to produce more sea animals like themselves, so that there would be many of them in the seas. The word "multiply" explains how they are to be "fruitful." (See: rc://en/ta/man/translate/figs-doublet and rc://en/ta/man/translate/figs-idiom)
"increase greatly in number" or "become many"
Let birds multiply
This is a command. By commanding that birds should multiply, God made birds multiply. (See: rc://en/ta/man/translate/figs-imperative)
"animals that fly" or "flying things." See how you translated this in Genesis 1:20.
evening and morning
This refers to the whole day. The writer speaks of the whole day as if it were these two parts. In the Jewish culture, a day begins when the sun sets. See how you translated this in Genesis 1:5. (See: rc://en/ta/man/translate/figs-merism)
the fifth day
This refers to the fifth day that the universe existed. See how you translated "the first day" in Genesis 1:5 and decide if you should translate this the same way.