Determining the gender of the fish is achieved in adult specimens by examining the black outer border of the anal fin. In female specimens, this consists of a fine black line, appearing almost as if drawn onto the fin with a fine pencil. In male specimens, particularly alpha males, the border is conspicuously wider, and in breeding alpha males, can cover up to a third of the total area of the anal fin. This is the only reliable means of differentiating gender in this species - while males frequently have taller and more pointed dorsal fins, some females also possess tall, pointed dorsal fins, and thus this characteristic is not reliable. Ripe females are fuller bodied, particularly when viewed from directly above, as the body cavity expands to accommodate the eggs.