Swordtails are a kind of fish that have a long, sword-like tail.
Swordtails are popular pets for fish tanks.
Examples:
I have a few swordtails in my aquarium.
The swordtails in the pet store are very colorful.
Do you like the way the swordtails swim?
The swordtails look like they have a little sword on their back.
My friend has so many swordtails in his fish tank, it looks like a rainbow!
The swordtails are the fastest swimmers in the tank.