Looking at fin length alone is not a reliable way to sex bettas, because there are long-tail and short-tail varieties. It's easy to confuse a male plakat for a female; pet stores do this all the time!

If you are trying to sex a baby betta (fry,) then these tips will generally not apply, as sexual dimorphism is not apparent until maturity. (Around 2-3 months of age.)

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The only fin you can reliably look at are the ventral fins.

• In males, they are wider, longer, and generally more bulky. Even in plakats.
• In females, they are slender and thinner, but can be just as long depending on the tail type.

The other fins in females are usually shorter then their male counterpart, but you'd need to know the tail type to accurately tell.

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One of the most reliable ways to sex a betta is to check for an "egg spot" or ovipositor. It looks like a pronounced white lump. This is found between the two ventral fins, behind the head.

Young females may not show their egg spot until they are old enough, and some are more pronounced then others.

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Male; note the bulkier body and curved head.

Female; generally has a more streamlined "feminine" appearance.