Pineapple sword is simply a color designation for a simple aquarium strain of swordtail. It is not a species designation and has no corresponding scientific name. Each one is worth exactly whatever you are willing to give for it. All aquarium strains of swordtails and platies are the result of cross breeding various true species of the Xiphophorus group. What it comes down to is that each breeder gets to name whatever he has bred and often they are unwilling to tell us how they went about it, who needs the competition after all. If you enjoy your fish and like the way it looks, that is all you can ask for. There are very few people who truly appreciate the distinctions between wild type fish that are true species. For most of us, the color and fin patterns we enjoy is all that enters into our fish choices.