it most certainly should be, the only thing that may or may not be visible as a juvenile are white spots. but most rostratums are not readily available as juveniles, so there is speculation there. rostratums usually have a longer snout, but thats not always true. the green dorsal spine line is the best way to tell which is which in most cases. its just my opinion, but i dont believe that is a rostratum species - genetically speaking it may be a hybrid, but from my experience and the photo you provided i believe it is just a black scopas.