I'm surprise that after lurking almost all of OP forum around the net,nobody had yet make a conclusion that Moria is a fishman.
Just look at him.
Doesn't he remind you of some eel or those deep angler fish?
I mean the jaws,it perfectly describe the description.
Moria have horn,Tom a fishman have horn too.
And let's not forget the title bestowed to him, "King of the Depth."
One more thing,try comparing him to that giant/fishmen dude who is from Foxy Crew,there's really not much difference.
Between him and Moria,who looks more like a fishman?
You decide.