Sexing:
Sorry Dave but it only works well with poeciliids. Goodeids do not have a gonopodium, instead they have a split in that same fin where the front part of the anal fin is shorter than the back part. Goodeidae means split fin. Functionally it is used much the same but it looks very different and if you are used to only poeciliids, it is confusing trying to sex them. The females also do not store sperm like a common livebearer but need to be freshly impregnated each time.This works with all other livebearers too. Males have a little "stick" (gonopondium?) while Females have a wide fin in that same area.