@Brook:
I think ''We have been waiting for him for 10 years, if he turns out to be a normal human living out in the sea instead of a fishman on fishman island, that'd be a huge One Piece mistake.''
But there's a chance of Jimbei being a Human that like Franky was raised by fishmen, or there are is also the chance that:
He's some merman tired of the shitty cliche of Merpeople being all kind with every creature and easy to trick, so he simply dumped the bunch of stupid fishmen that he tricked into helping him with a fake respect/friendship and decided to join the WG in order to rule the bottom of the sea with iron fist…
Or Jimbei possibly is a "kind" fishman who lied to his crew in order to save them from being killed off by the WG, so that's how Arlong became an evil bastard who hated humans because they took away Jimbei from him, but before we think Arlong's Gay, we find out that......JIMBEI'S A WOMAN...sigh
Or Jimbei would be a one shot character that will be killed off by some supreme force to show the force of said....supreme force...<_<
Or Jimbei's a Megalodon who eventually got bored of his crew after he surpassed Arlong in terms of species, assuming that if he's a megalodon, then his species growth is slower than any other species out there, explaining why him and Arlong were once equals...
Or Jimbei's a Remora, wich would be surely a shock for everyone...