Avoiding Breeding in Livebearers

Question
Hi!

I have a 10 gal tank and enjoy livebearers.  My concern, however, is avoiding their breeding (I have raised fry in the past, but would like to avoid).  Will most livebearers interbreed easily with other livebearers?  Or will getting certain types that are very different from each other help to avoid this?  How can I sex them easier?  I have had lots of swordtails in past cause they are so easy to sex, but would like to include mollies, guppies, platies, etc. in my tank.  Do you have an recommendations as to avoiding breeding?  

Thanks!

Answer
Male Guppies and Platies are fairly easy to sex as they have a gonopodium (a curled/tube-like anal fin).  If you keep a tank of all males, you will have a problem with aggression and the smallest males will always be picked on.  I would avoid Mollies, as they are aggressive to smaller breeds like guppies and prefer different water conditions.  If you would like to keep males and females in the same tank, you can always get a secondary species to control the fry population, such as Betta.  Some fry would make it to adulthood, but most would get eaten.