Adam Clarke on Jonah 2:6

I went down to the bottoms of the mountains - This also may be literally understood. The fish followed the slanting base of the mountains, till they terminated in a plain at the bottom of the great deep.

The earth with her bars - He represents himself as a prisoner in a dungeon, closed in with bars which he could not remove, and which at first appeared to be for ever, i.e., the place where his life must terminate.

Yet hast thou brought up my life - The substance of this poetic prayer was composed while in the fish's belly; but afterwards the prophet appears to have thrown it into its present poetic form, and to have added some circumstances, such as that before us; for he now speaks of his deliverance from this imminent danger of death. "Thou hast brought up my life from corruption."