Guys, It was a Leviathan.
"There are very few people who have not heard the story of Jonah and the big fish. Most believe the big fish to be a whale, since we think of this as the only sea creature large enough to swallow Jonah whole and sustain his life in the interim. Some argue that it could not be a whale, because the scripture uses the word, "fish," and a whale is a mammal. This last argument is a typical interpretation error that arises when one tries to exegete scripture using English translations. The Hebrew word used here is "dag," which is usually transliterated as "Leviathan" and is simply used to refer to a large sea creature. We don’t know what kind of sea creature seized Jonah from the ocean waves, but we know that something did."
http://www.biblicaltheology.com/jon/32_01_17.html