Radak: Lower creations should praise Hashem.

Malbim: After descending in the development of existence until the land, which is the lowest, it begins to rise. First it discusses the four 'elements'. Taninim and Tehomos are [in the element] water.

Rashi: They are giant fish. Radak - they are bigger than land animals - "va'Yivra Elokim Es ha'Taninim ha'Gedolim" (Bereishis 1:21).

Radak citing his father: People who see them and contemplate them should praise Hashem for His wonders.

Radak: It is the water under the land and on the land. It mentions the water before the land, like it was at creation.