Hi Samk

Until arowanas reach its maturity age, it's quite difficult to tell whether its a male or female. Sexual differences becomes more apparent as they reach 3 - 4 years old which is based largely on body contour and size of the mouth cavity.

In general, it's said that males have a slender body, a bigger mouth (hence a relatively larger head) and more intense colours. The larger mouth functions as a "incubation chamber" for the eggs. Males are known to be more aggressive during courtship and competition for food.

cheers