וַיְבָ֧רֶךְ אֹתָ֛ם אֱלֹהִ֖ים לֵאמֹ֑ר פְּר֣וּ וּרְב֗וּ וּמִלְא֤וּ אֶת־הַמַּ֙יִם֙ בַּיַּמִּ֔ים וְהָע֖וֹף יִ֥רֶב בָּאָֽרֶץ׃
And God blessed them, saying: ‘Be fruitful, and multiply, and fill the waters in the seas, and let fowl multiply in the earth.’
Rashi on Genesis
ויברך אותם AND HE BLESSED THEM — Because people decreased their number, hunting them and eating them, they needed a blessing (Genesis Rabbah 11:2); it is true that beasts also were in need of a blessing, but on account of the serpent that was to be cursed in the future, He did not bless them, in order that it might not be included in the blessing.
Rashbam on Genesis
ויברך אותם אלוקים, you will note that all the categories of living creatures whom G’d created were blessed by Him.
Sforno on Genesis
ויברך אותם אלוקים, seeing there were so many of them they would not achieve their purpose in this universe without such a Divine blessing.