Yahweh prepared a great fish to swallow up Jonah, and Jonah was in the belly of the fish three days and three nights.
As to what kind of fish this was, there is utterly no way of knowing. Many scholars have needlessly exercised themselves in trying to help God out (!) by finding a record of some great fish that could actually swallow a man; but such "findings" have no value at all.  The event here described is clearly beyond nature and above it.  The supernatural is written on every word of this narrative.  In nature, there is no such thing as a fish that could swallow a man without killing him; and it is a futile kind of vanity that looks for such a thing.  As a type of the death, burial, and resurrection of Christ, this event was designed to be altogether above and beyond the ordinary occurrences in the realm of nature.