I originally thought it might be a female dragon knife but they are white, I do agree it looks exactly like apteronotus bonapartii they get about 10.5"
OP's fish is A. bonapartii.
Parapteronotus has much smaller scales and also most of them have a faint white/yellow stripe down the back. A. bonapartii also has a white spot at the base of the caudal fin and can have a pretty wide range of head shapes (see photos).
Parapteronotus has much smaller scales and also most of them have a faint white/yellow stripe down the back. A. bonapartii also has a white spot at the base of the caudal fin and can have a pretty wide range of head shapes (see photos).
