Male betta fish look significantly different than females. Males are brightly colored, and their fins are often a different hue than the rest of their bodies. Females have drab colors and matching fins.
Male bettas' fins are typically longer and fuller than females' fins. Some males have fins so long that they get in the way while swimming. Females' fins tend to be short and rounded. Adult males also have bigger and longer bodies.
Male bettas also display different behavior than females. A male is more aggressive, flaring its fins and challenging other bettas of the same sex. Because of the likelihood of fighting, betta fish owners should never keep multiple males in the same tank.