Yahweh prepared a great fish to swallow up Jonah, and Jonah was in the belly of the fish three days and three nights.
It really serves no purpose to find examples of extraordinarily large specimens of ocean life such as the Mediterranean white shark, and others, which are alleged to have swallowed men, or even horses; what of it?  No such event ever heard of even approaches what is said here of Jonah.  This is intended as a sign from God, the particular sign to which Jesus appealed in his struggle against the Pharisees, and the one which he made, preeminently above all others, the sign of his own death, burial and resurrection  (Matthew 12:38-40).