Jonah 1:17 (ESV) … “And the Lord appointed a great fish to swallow up Jonah. And Jonah was in the belly of the fish three days and three nights.”
The Holy Spirit assures us that “the Lord had prepared a great fish to swallow up Jonah,” (kjv) a fact that unbelievers have viewed with incredulity. The word translated “prepared” literally means “appointed” or “assigned,” so the fish was not specially created for the occasion. In some translations of Matthew 12:40 we are told that a whale swallowed Jonah, but the Greek word rendered “whale,” ketos, can refer to any large sea monster. The word cetaceor, which is related to the word ketos, signifies the mammalian order of fish.
Ignorant people have said that a whale could not swallow a man, but a giant sperm whale that certainly could have swallowed a man is exhibited in the Smithsonian Institute in Washington, D.C. Captured off Knight’s Key, Florida, in 1912, this whale is forty-five feet long, has a mouth thirty-eight inches wide, and weighs thirty thousand pounds. A fish in its stomach at the time it was captured, weighed about fifteen hundred pounds.
Numerous stories of men being swallowed alive by whales—and surviving the ordeal—have been validated. In February 1891 the crew of the whaling ship Star of the East sighted a large sperm whale off the Falkland Islands. They harpooned the whale and in its death throes it swallowed a man named James Bartley. A day and a half later his shipmates, who thought he had drowned—found him unconscious in the whale’s belly. Bartley lived to tell about it and his story was published in the newspapers. Describing his sensations as he slid into the innermost part of the whale, he said he could breathe easily, but the heat was unbearable. His whole appearance was changed by the ordeal, for his neck, face, and hands, which had been exposed to the whale’s gastric juices, were permanently bleached to a livid whiteness. This story gives us an idea of what Jonah experienced when he was imprisoned in the “great fish.”
Jonah was in his prison “three days and three nights” and much debate centers around whether or not he died while he was there. The Lord referred to Jonah’s ordeal as a type of His death, burial, and resurrection. In Matthew 12:40 the parallel is exact: “As Jonas was three days and three nights in the whale’s belly; so shall the Son of man be three days and three nights in the heart of the earth.” A man who was miraculously kept alive for three days and three nights does not seem to be an exact parallel of the Lord, who was dead and buried for three days and three nights. So the likelihood is that Jonah died in the belly of the fish and was miraculously resurrected at the end of the third night. Probably Jonah uttered his prayer just before he lost consciousness. The Hebrew idiom translated “three days” can refer to parts of three days, but the expression translated “three days and three nights” must be taken literally. 
Life Application: The Lord is always greater than what we seek. As the sea closes over Jonah, there is every reason to think that the chapter has closed. But hidden from view, a great fish has been commissioned by the Lord, its appointed task being to swallow Jonah as he sinks into eternity.
God does not leave Jonah in the deep. He has been chasing a runaway, but now that he has caught him, the plan is far greater than punishing him. Certainly Jonah’s experience is unpleasant and humbling, but God’s purposes are essentially restorative rather than punitive. We see Jonah’s restoration in what follows in the remaining story.
 Phillips, J. (2009). Exploring the Minor Prophets: An Expository Commentary (Jon 1:17). Kregel Publications; WORDsearch Corp.  Mackrell, P. (2007). Opening up Jonah (p. 49). Leominster: Day One Publications.