The gen complex for the trait Swallow extends all fins. This means that the males are not able to mate anymore because of their extended gonopodium. To breed theses fish, you need related non-swallow males to cross with the swallow females.
Swallow Tail Guppies are not for beginners. Their long fins slow them down quite a bit and together with other fish they are often too slow when feeding time comes around. The long fins are also vulnerable for nipping. Therefore it's best to keep them on their own - this will ensure they always get enough food and they stay healthy and beautiful. The females get quite big; the biggest albino female I had so far was 6cm long without the fins.
My strain carries the Swallow trait as well as the Elongatus trait. This means fish that aren't expressing long fins due to Swallow will still have extended dorsal fins.