Thank you Wimmels, after having looked on various descriptions of the Fusco i am pretty sure it is the one that i have got.
It's in with a GT that is twice as beefy as the Fusco, both around 10", and a pair of Salvini's where the male is 8" and the female is 4,5". And a RBP at 1,5" which the Fusco sometimes seems to look at as food, but it never really acts on it *crossing fingers*
I'm keeping him well fed (overfed actually) untill the RBP get's a little more beef to it.
Luckely it's a 2,5 feet tall tank that i have them in, and the piranha just cruises the surface with my asian shooter fish (don't know the latin name, but it's the one that shoots up on insects from underneath the surface) and they get along great.