I finally watched the Prince of Egypt last night and I saw this scene in context and realised what it actually was.
People thought it was a whale, then they thought it was a Megalodon Shark which made sense to me when I saw the gif except for the fact that they died out millions of years before this story. And then seeing the reaction of the little girl and her Grandma, the kid is terrified but her Gran reassures her like it’s nothing to worry about which is what really helped me figure it out. That kid thought it was a huge Shark too. Well no, it ain’t and Grandma knows what it is, she knows that it’s harmless.
One thing I always noticed was that it’s got the tail of a shark but the head of a whale. Now what has a whale head and a shark tail? A WHALE SHARK. They inhabit the Red Sea and the largest Whale Shark on record was 12.2 metres long but they believe them to grow even bigger, to the size of a bus. Ergo it has to be a Whale Shark.