Albert Barnes Commentary Psalms 148:7

"Praise Jehovah from the earth, Ye sea-monsters, and all deeps." — Psalms 148:7 (ASV)

Praise the Lord from the earth - From among those who dwell on the earth. In respect to terrestrial objects, let these also unite in the praise of God.

You dragons - On the meaning of this word, see Psalms 91:13, note; Isaiah 13:22, note. The word may mean a great fish, a whale, a sea monster, or a serpent. It would seem to refer here to whales and sea monsters. See the notes at Revelation 12:3.

And all deeps - All that are in the depths of the sea. Not merely the “dragons” or sea monsters, but all that inhabit the oceans.