The bible doesn't say. Only a whale has a gullet big enough to pass a man, and a whale is not a fish.
People often speak in figures of speech, so the bible does too. A figure of speech is a departure from the normal patterns of language for the purpose of emphasizing something. The simplest figure of speech is the SIMILE. A simile emphasizes a similarity of two things by merely saying it: "You are like a dog", or "You are as a dog". The figure rests entirely on one word.
A METAPHOR emphasizes a similarity of two things by saying they are the same; "You are a dog".
Next comes a big word: HYPOCATASTASIS. This is a Greek word for name-calling. Hypocatastasis just calls the fellow "Dog!" See Luke 13:32 "that fox", and Genesis 3:1 "the serpent".
A PARABLE is an extended figure of speech; a story based on a simile, metaphor, or hypocatastasis. If the story is possible, it is a MYTH. If the story is impossible, it is a FABLE. If a fable includes an explanation of the meaning, it is an ALLEGORY. Don't confuse any of these with LEGEND, which is a supposedly true but unverified historical account (Adam and Eve, for example).
Jonah is a fable.
These terms are not used with any precise meaning in modern discourse. For instance, most people think 'allegory' means "a story full of religious symbolism beyond human comprehension". But when discussing figures of speech they are very precisely defined. Here is a book that lists about 900 figures found in the bible. It is almost the only work in the subject for the last two thousand years:
You can get a hard copy at any bible book store.
The Son of God, Jesus Christ himself testified to the truthfulness of the account about Jonah's being swallowed by a " huge fish".
Matthew 12:40 Jesus said : For just as Jonah was in the belly of the huge fish for three days and three nights, so the Son of man will be in the heart of the earth for three days and nights.
The Bible simply states that " Jehovah appointed a great fish to swallow Jonah." The kind of fish was not named.
There definitely are sea creatures capable of swallowing a man, among them being the white shark and the sperm whale.
The Bible tells us at Jonah 1:17, ‘Jehovah now sent a huge fish to swallow Jonah, so that Jonah came to be in the belly of the fish for three days and three nights.’ The Bible never specify what type of fish swallowed Jonah but there are a few fish that is capable to swallow an adult without damaging them.
According to the Bible this miraculous event was only possible because of Jehovah God making it possible for Jonah to come out after three days of the fish belly alive. This is not a fairy tale for it is recorded in the Bible to teach us the power, mercy and love Jehovah has for us. It also teaches us the blessings of obedience and the consequences of disobedience. In the end Jonah learned a good lesson on relying on the Grand Creator. It leaves a model for us to follow so we could have Jehovah’s blessings also.