This wolf came from the Xingu as mentioned. And to be exact in ALtamira, XIngu. So that tells us it cant be a Lacerdae because this species is restricted to Ribeira de Iguape River in Southern Sao Paulo. Is it a black wolf? well... it doesnt seem to be a black wolf to me because those are pretty dark in colour. It seems the fish has a tiny rounded dark spot near the dorsal edge of the caudal peduncle. And if this is so then its a it´s a malabaricus indeed.

Good answer krswop1 amd Mudfrog. I guess i posted it because the shape of the head seemed interesting to me.