In this forum I've seen people buy a fish of a certain gender but then it turns out the fish is the opposite gender. I decided to make a thread pointing out some of the differences between a male and female betta.
The fish on the left (yellow) is a male. The fish on the right (silver) is a female. They are both HMPKs.Here are some of the basic differences.
1. Dorsal fin: The male's dorsal fin larger and fuller than the female's dorsal fin. Also the female's dorsal starts futher back on the spine than that of the male's.
2.Operculum (beard): When a male flares he opens his operculum and displays his membrane. Females also flare but females' operculums are smaller than males'.
3.Ventral fins: A male's ventral fins are longer than a female betta. A female betta could have long ventrals (for example Veiltail female) but they are still smaller than males'.
Other differences: Females have an egg spot called an ovipositor.
When ready to breed female bettas get breeding stipes( Vertical stripes along her body). They also develop eggs.
Female betta's also have shorter fins than males.
Hope this helps. If anybody has anything else to add, feel free to do so.