Jonah's sojourn in the belly of the whale is part of the metaphorical story of a prophet sent to non-Israelites against his will. Even after the Ninevites did penance, Jonah was still angry as he would have preferred they be destroyed.
The Jonah story conveyed to the Israelites that God was the God of all men, not just the Israelites, foreshadowing Christ, who would come to save all men, not just the Jews.
Whatever was I thinking reading and believing the Early Fathers of the Church and their wrong-headed ideas about the historicity of Jonas(shall I list them all for you, brother?) when all I had to do was ping you for the definitive answer.
Sinkspur locuta est, Causa finita est :)