Most strains of angelfish available in the fishkeeping hobby are the result of many decades of selective breeding. For the most part, the original crosses of wild angelfish were not recorded and confusion between the various species of Pterophyllum, especially P. scalare and P. leopoldi, is common. This makes the origins of "domestic angelfish" unclear. Domestic strains are most likely a collection of genes resulting from more than one species of wild angelfish, combined with the selection of mutations in domesticated lines over the last 60 or more years. The result of this is a domestic angelfish that is a true hybrid, with little more than a superficial resemblance to wild Pterophyllum species. Much of the research into the known genetics of P. scalare is the result of the research of Dr. Joanne Norton, who published a series of 18 articles in Freshwater and Marine Aquarium Magazine
