“great fish.” Although the REV translation reads “fish,” we do not really know what swallowed Jonah. The reading “fish” comes from Jonah 1:17, but the Hebrew text allows for other sea creatures besides fish, including whales.” Today we very carefully classify life into things like phyla, genus, and species, and if the book of Jonah was written in modern times we would know exactly what swallowed Jonah. But the ancient classification of animals and sea life was much less exact than ours, and it was based on different standards. For example, we make a distinction between a “fish” and a “whale” based on things like whether it breathes air with lungs or via gills. Thus, a “fish” can be big or small, but they all have gills. Similarly, a “whale” can be big or relatively small—the dwarf sperm whale grows to only 8 feet and is much smaller than many “fish”—but all whales have lungs. But the ancient cultures and vocabulary did not make those exact distinctions, so we cannot tell from the ancient Hebrew (and Greek too) vocabulary whether what swallowed Jonah was a fish or whale, all we really know about the creature is that it was big enough to swallow Jonah whole.
Also, the text says, “Yahweh prepared a great fish to swallow up Jonah,” so it is also possible that the creature that swallowed Jonah was not normal, but was some kind of aberration that God prepared so Jonah could be swallowed whole and be in the creature for three days and nights without being substantially damaged. The lack of exact knowledge of what swallowed Jonah explains the difference in the English versions. Although almost all English translations of Jonah 1:17 read “fish,” the identity of the creature in Matthew 12:40 is much more diverse, which seems strange since it seems that what swallowed Jonah according to the book of Jonah would be reproduced in what Jesus said about Jonah, but nevertheless the English versions differ: “fish” (HCSB, ESV, NIV, NLT); “whale” (ASV, KJV, NAB, RSV ); and “sea monster” (CJB, NASB, NJB).
“and Jonah was in the belly of the fish.” Jonah died inside the fish and was dead for three days and three nights, just as our Lord Jesus was dead in the grave for three days and three nights (see commentaries on Matthew 12:40 and Jonah 2:1). Sadly, the vast majority of the Christian world does not know about Jonah dying inside the fish and the Christian art is most unhelpful. Although most show Jonah kneeling in prayer, some pictures show Jonah in the fish sitting beside a campfire, while one picture that is likely for children showed Jonah with a chair and TV set!