How to tell male and female Betta fish apart?

Telling male from female Betta fish relies on these features. First, look at fin size and shape: males usually have longer, wider, brighter fins; females have shorter, duller fins. Second, look at body shape: males are slimmer but with a larger tail; females are plumper with a smaller tail.

Finally, look at the genital pore: a female has a clear white-yellow ovipositor between the ventral and anal fins, while the male does not.