Before this subject is discussed two points should be emphasized. (1) The miraculous element is underlined at the beginning, “The Lord had appointed (‘prepared’ KJV) a great fish to swallow up Jonah” (Jonah 1:17); (2) The Lord explicitly stated that this was fact (Matt 12:40).
The tr. of “fish” is not possible (nor necessary); some of the toothed whales are physically capable of swallowing a person. Several species can swallow whole seals and dolphins weighing several hundred pounds. There are cases of reasonable authenticity of men being swallowed alive and liberated shortly afterward. The sperm whale of this group comes into the Mediterranean and appears from time to time off the Pal. coast. It could have been such an animal that was appointed for this task, but there is no point in speculating about the full physical explanation of an incident that primarily is metaphysical, i.e. miraculous.
International Standard Bible Encyclopedia (1915)
(1) ketos (Sirach 43:25 (the Revised Version (British and American) "sea-monster"); The So of Three Children verse 57 (the Revised Version (British and American) "whale"); Mt 12:40 (the Revised Version (British and American) "whale," margin "sea-monster"; the King James Version "whale" throughout)).
(2) tannin (Ge 1:21; Job 7:12), "sea-monster," the King James Version "whale."
(3) tannim (Eze 32:2), "monster," the English Revised Version "dragon" the King James Version "whale" the King James Version margin "dragon."
It will be seen from the above references that the word "whale" does not occur in the Revised Version (British and American) except in The So of Three Children verse 57 and Mt 12:40. Ketos, the original word in these passages, is, according to Liddell and Scott, used by Aristotle for "whale," Aristotle using also the adjective ketodes, "cetacean"; Homer and Herodotus used ketos for any large fish or sea-monster or for a seal. It is used in Euripides of the monster to which Andromeda was exposed. In the Hebrew, in the Book of Jonah, we find dagh or daghah, the ordinary word for "fish": "And Yahweh prepared great fish to swallow up Jonah" (Jon 1:17). Whales are found in the Mediterranean and are sometimes cast up on the shore of Palestine, but it is not likely that the ancient Greeks or Hebrews were very familiar with them, and it is by no means certain that whale is referred to, either in the original Jonah story or in the New Testament reference to it. If any particular animal is meant, it is more likely a shark. Sharks are much more familiar objects in the Mediterranean than whales, and some of them are of large size.
In Ge 1:21, "And God created the great seamonsters" (the King James Version, "whales"), and Job 7:12,
"Am I a sea, or a sea-monster (the King James Version "whale"),
That thou settest a watch over me?"
The Hebrew has tannin, which word occurs 14 times in the Old Testament and in the American Standard Revised Version is translated "monster," "sea-monster," or "serpent," and, exceptionally, in La 4:3, "jackals." the King James Version renders in several passages "dragon" (compare Eze 29:3 the English Revised Version).
See Dragon; Jackal.