OK i have a tropical fish tank, the guppies and mollies wont stop having babies what fish will eat the babies?

the tank is 60 gallons and i was thinking of getting a crayfish. the tank is getting over run by all these guppies and i need a way to get rid of them, i dont want to just kill them, but get a fish or other animal to eat ONLY the babies, or at least not wipe out the fish population... any suggestions on how to get everything under control?