I don't think you will get a deffinate number. There are currently 4 described species (H. efasciatus, H. notatus, H. severus, H. spurius), two undescribed species (H. sp. 'Rotkeil', H. sp. 'Atabapo'), two man made color forms (gold, red) and an uncounted number of local variants of the existings species, especially greens (H. efasciatus). A couple of the well known green variants include Turquoise and Tapajos red heads, but each river has slightly differant colorations ranging from brown to green to blue.