Maybe it's Arlong because Ruffy broke his nose. And maybe he has now a shorter nose. ^^
But if the kidnapped Hachi is the one from Arlong's old crew, then "Dupal", or whatever he's called, isn't Arlong. I don't think Arlong would kidnappe an own friend of himself.
More possible is it that it's Creek or someone from before the story or something like that.
If Eneru hadn't been on "Very Worth", then I would think it's Eneru, but why should he wear a Iron mask? I don't know.
I hope we'll see it next week.
D