Thanks again, Hendre.
Finally got a good look- the "projection" has a distinct backwards angle, and is a little longer than in your picture = male.
Q#2: a few months on and the belly is still very fat, but growth has greatly slowed/stopped. In fairness the species has a reputation for slow-growth and the water quality's likely very "alive" but also likely not pristine in the grow-out tank, and there is quite a bit of grub to be had for anybody willing to grub for it. I am interested in internal parasites considering the whole bunch in the shop had this fatness and he's not lost it. If so, I'd also be interested in how I might set about eliminating such parasites.