What feature defines the male swordtail compared to the female regarding the caudal fin?

Answer

The male possesses a lengthened, sword-like lower ray.

The most defining characteristic separating the sexes is the male's namesake 'sword,' which is a lengthened, sword-like lower ray on the caudal fin; females completely lack this appendage.

What feature defines the male swordtail compared to the female regarding the caudal fin?
fishfreshwateraquariumcharacteristicswordtail