This verse marks a turning point in the book, as Jonah himself now prays. Up to this point there is no indication that he followed the example of the heathen sailors by praying on board ship. The usual verb “to pray” is only used twice in the book, here and in 4.2; elsewhere the verb used is “to call.”
A literal rendering of From deep inside the fish might suggest that Jonah was at “the bottom of the fish.” This, of course, is not necessarily implied; it simply means that Jonah was “well inside the fish.” Therefore an equivalent rendering might be “From the very inside of the fish” or “From right there inside the fish.”
The expression his God implies in this context the existence of other gods, as in 1.5, where “god” has no capital letter, the point being that there the reference is to the gods of the heathen sailors, but here to the LORD, the God of Israel. The genitive here bears no sense of exclusive possession, but simply means the God whom Jonah worshiped (1.9). As a prayer from inside the fish, the language of thanksgiving may seem somewhat premature.
For languages that require a possessive relationship with “Lord,” it may be possible to translate “his Lord, that is, his God.” In other instances a more satisfactory rendering may be simply “his Lord God.” A rendering such as “his Lord who is God” would presume a kind of exclusive meaning of monotheism that may be judged inappropriate for this type of context. At the same time one must recognize that in a number of languages one cannot speak of “his God” but simply as “the God whom he worshiped,” since it may be quite inappropriate to speak of “possessing God.” Compare the statement made in connection with verse 5 of chapter 1.
Quoted with permission from Clark, David J. et al. A Handbook on the Book of Jonah. (UBS Helps for Translators). New York: UBS, 1978, 1982, 1993. For this and other handbooks for translators see here .