פּירוש אויף בראשית 1:22

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.

פרו ורבו בימים והעוף ירב בארץ, “be fruitful and multiply in the oceans, and let the birds multiply on earth.” The reason why G-d did not extend a similarly worded blessing for the mammals was so that they should not increase at a faster rate than the human race and man would not be able to prevail against them. Birds and fish whose habitat is the airspace and the seas respectively, do not pose a similar problem.

And God blessed them: And so [too] (Genesis 2:3), "And God blessed the seventh day." Behold, you have learned [from this] that one who acquires a new thing should make the blessing of 'shehechianu.'