What Kind of piranha is this

[M|L]

not all black rhoms turn black.

that's why those that ARE black are more expensive.

it's a VERY nice rhom for sure.

not sure the variant of it, but looks like a high-back.

 

[Blue]

Lots of factors determine the physical appearance, the only really concrete info you can say more than S. rhombeus would be where it was caught. More than that and it's all qualitative judgement of the appearance.