There are several species of severum, and most golds color up with red. Species Rottkiel is also a really nice fish, but rarer so price is up there. There is the green, turquoise, and another that puts all of them to shame, but I can't remember the name.............oh yeah, guyana, which is yellow green, but remarkable. As far as size, they can attain 10" Or basically the size of a dinner plate. Depending on tank size is how many you should have. Under 100 gal, only one is recommended.