Mesonauta festivus, commonly known as the Flag Cichlid, is admired for its elegant, laterally compressed body and striking coloration. The body is typically silvery with vertical black bars that become more pronounced with age or during stress. A subtle iridescent blue-green sheen can be seen on the flanks and fins under good lighting.

Males are slightly larger and may display more intense coloration during the breeding season, while females are smaller and less vividly colored. Adult size generally reaches 12–15 cm.