Now, the text doesn’t say “God appointed a whale” but just “a great fish.” Both the original Hebrew dag gadol and the Greek of the Septuagint, kētei megalōi, translate as “huge fish.” Archaeology has proved that the Mediterranean was once home to a great variety of whales —which the Romans hunted almost to the point of extinction. It might be the case that the author of the biblical text simply wanted to contrast Jonah’s “closed mouth” to that of the “big fish,” able not only to swallow a whole human being but also being hollow enough as to provide him with safe shelter for three days and three nights. Interestingly enough, during those three days Jonah certainly keeps his mouth open — he seems to spend them praying out loud.

But how did this “big fish” turn into a whale and not into one of the 47 species of sharks found in the Mediterranean? It seems St. Jerome is to blame.

https://aleteia.org/2021/07/15/jonah-was-not-swallowed-by-a-whale