Not a really good characteristic to use to ID all species. I'd leave it as just one of many that stand out on armatus. I have owned a redtail that was purely silver and black. No red fins, no gold body, no color in adipose fin. The black blotches on the gill plates can be used to differentaite between Scombs (a round dot) and the other two (armatus and Redtails, which have a more crescent moon shaped black blotch). Scombs also bave black blotches where the pectoral fins meet the body, Armatus and redtails dont. Scombs tails are also a lot different that the other two, both in structure and color. Scombs have more of a rounded shape to their tails, and they have a grey base with a clear edge. Redtails and Armatus have more points on their tails. They also have a spine runs from the middle out. Tail color for redtails can vary a great deal, from yellow, to grey, to maroon (these are just a few of the color varients I personally have seen). Armatus seems to have a lot bigger tail in proportion to the other species. They also seem to share the common colors, which fade from a goldish color to a black band to a clear edge(when younger) or white edge(when older). It also appears that going from the smaller species (scombs) to the largest (Armatus) the overall mouth to body angle straightens out. Armatus are more streamline, while scombs heads tilt up the most. Redtails are somewhere inbetween. Armatus are a lot thicker boddied, then redtails, then scombs. Same with the teeth size, and aggression levels. Sorry I wrote this kind of fast. If you have any questions, or need me to clarify anything, don't hesitate to ask. Hope this helped.