How do you tell if a betta fish is a male or female?

The breeds of fighting fish can vary, although usually male bettas have the long, flowing fins that make these fish so popular. Females have short, rounded fins, similar to the original wild betta. It is, however, possible to find males with natural fins for sale. These are usually sold more for sport fighting than the pet trade. Females and wild males rarely have the bright colors bred into them and generally have dark brownish bodies with barred patterns and red and blue fins.

the male has long fins and the female has small short fins

Put two beta fish together in one bowl, if they start fighting, you know they are both males.