sometimes when a hybridizing occurs its like it can decrese tha genetical stability of certain things so basically sometimes they lose immune system immunity and otha things like basically they can be real weak...
Its not that they have shorter life spans its that they have a very small servival ratio when breeding, buy the time they are selling size (2inches) its up to who ever as the fish weather or not it lives if your dont know how to take care of it, it will die.... But I'm sure if you can keep a regular dempsy you'll be fine...