Dusky Damselfish

The Dusky Damselfish is a dark-colored, powerfully territorial species famous in marine biology for its remarkable algae-farming behavior. Adults display a uniformly dark brown to black coloration with subtle dark scale margins, giving them a somewhat somber but dignified appearance. Juveniles may show a small blue ocellus near the dorsal fin base that disappears with age. At up to 5.5 inches, this is one of the larger commonly encountered damselfish species.

In the wild, Stegastes nigricans is one of the most extensively studied damselfish species due to its sophisticated farming behavior. Each individual maintains a carefully cultivated garden of preferred filamentous algae within its territory, actively weeding out undesirable algae species and aggressively defending the plot against all herbivores. Research has shown that these algae gardens are distinct from surrounding reef areas, with the farmed plots supporting specific algal communities that the fish preferentially consumes. The Dusky Damselfish will fearlessly attack fish, sea urchins, and even human divers that venture too close to its garden.

In the aquarium, the Dusky Damselfish is supremely hardy and nearly indestructible, tolerating water quality fluctuations that would harm more sensitive species. However, its intense territorial aggression makes it one of the most challenging damselfish to house in a community setting. Adults will claim and defend a substantial area of the tank, attacking any fish that approaches regardless of size. Only large, robust, and assertive tankmates should be considered. The species is reef-safe from a coral perspective, though it may actively cultivate algae patches on rockwork and become especially defensive of these areas.