How does a swordtail fish breathe?

For one you need to be able to tell the difference between male and female.

Males always have the sWord on their tail and are normally bright coloured or speckled. Females don't have the sWord and look anything between whitey grey to orangey or yellowy even speckled.

If a female is pregnant you will start to notice her baby bump in a week or two. It is a good idea that you separate her or even better put in a few LIVE plants or hidey holes for cover so the baby fish can hide so they wont be eaten by their mother or father or anyone else for that matter.