You can’t grade the arowana when from a young age. You are basically taking a gamble when buying SR arowanas; can either turn out to be brightly coloured with brilliant red scales or an arowana with not so prominent reddish scales. That’s why adult arowamas cost more depending on their grade when adults not juveniles.
Long pectoral fins, large V shaped tail, signs of red colour on cheekare there certain fin and tail traits, body shape etc to look out for at the very least??