hippos are pretty freaky when you go near a huge one, though I guess you get used to them
(even with the protective wall/glass you find at the zoo :lol)
I am a biology student at uni and from what I can remember from marine biology is the sunfish is firstly a very inefficient swimmer due to its crazy shape and also a very old species of fish.
And yes they grow that big
Also hippos kill the 2nd most people out of animals each year in africa (I think)
Mosquitoes being number one pretty much all over the world expect deserts and cold environments.