Finally a post from a professional.. i was losing hope in the users that visit the piranha forum..
Listening to people that dont know anything argue is actually quite amusing
To the question at hand:
A rhombeus is a rhombeus, and thats that.. Though some localities tend to produce rhoms that look a certain way, there is no way to pinpoint where the exact fish came from. You have a very nice rhom there and you should be happy with that. I would also reccommend getting him onto some type of food that doesnt include live, and feed him as much as posible as often as he will eat. The novice post earlier about him being a "high back" is just pointing to the area in which you can tell that this fish is underfed and extremely malnourished and the potruding bone will dissappear into his fat stores when he gains a little bit of weight..
And a word of advice..
You may want to listen a little more closely to the people here that have piranhas in there signature, these are the people that tend to have a bit more knowledge when dealing with these fish... theres just only so much you can learn from books..
Happy posting