Everything good on this movie is derivative from the first one. This rest is completely nonsense, from the poor screenplay to the vague corespondency to a timeline on History.
Sharks inside the Colesseum are a minor problem on a story that lacks coherence, and anybody even drafted any response every time there is a major revelation or a plot twist.
A great cast completely wasted by giving life to shallow dialogues, in a film whose only reason to exist is to generate stupid entertainment, just like the "circus" that the Romans provided in the gladiator arenas.