a few words
just a little word about keeping livebearers there are the type that you get out of your local fish shop which have been in the hobby for years and sometimes have been cross bred i.e. the swordtail with the platy or with some sub-species i am not talking about them i am talking about the pure/wild types.
you should not mix fish which are pure/wild types which have the same family (genus) because they may cross bred and mix up the strain if you have limited space for tanks then you can put 2 species in the same tank but not from the same genus i.e. a poecilia and heterophallus but not a x. helleri and a x. cortezi as they may cross
so if possible keep 1 species to 1 tank or a mix of genus to a tank and remember to have a spare tank for the fry and an algae leaden tank brings the fry on better and once you have bred and raised your fry pass them on
by the way that was a hint :-)