The Stegastes nigricans, of the order of Perciformes and family Pomacentridae (Damselfishes) is commonly known as the Dusky Gregory, Dusky farmerfish, Black damsel amongst others. The overall body colour is brown with a darker patch at the rear of the dorsal fin. Lavender markings can be seen on the head. Courting males have a large white band across the body and white stripe from the snout to the pectoral fin base. It has a total of 12 dorsal spines, 15 to 17 dorsal soft rays, 2 anal spines and 12 to 14 anal soft rays. Juveniles range from yellow to orange brown with a brown area from the upper head to the black dorsal fin.
This species is present across the Indo-Pacific region. It is found in colonies of Acropora corals. The recorded depth range is between 1 to 12m. The diet consists of algae, gastropods, sponges and copepods. It maintains filamentous algae that grow on dead corals. This species is territorial and will attack humans getting too close. It becomes more aggressive during reproductive periods. It emits a clicking sound when displaying aggression. During breeding season, several females can visit a nest, tended by a male.
The conservation status of this species has not been evaluated yet.
This species can reach a maximum recorded length of 14 cm.