Stegastes nigricans

Stegastes nigricans, the dusky farmerfish, is a species of damselfish found around coral reefs at a depth of one to 12 meters, in tropical climates between 30°S and 30°N. They are known for farming monocultures of algae such as cyanophores and rhodophytes. It has an average length of 9.0 cm, but can reach lengths of 14.0 cm. It has 12 dorsal spines, and 15 to 17 dorsal soft rays. It also has 2 anal spines and 12 to 14 anal soft rays. Adults are generally brown, with the dorsal parts of the head and nape being darker, grading to tan on the lower parts of the head and breast. The scales have darker brown margins. The lips are whitish, the suborbital is mostly blue, and the preopercle and opercle scales have blue centers. The median and pelvic fins are brown, the pectorals are dusky, and sometimes there's a well-defined dark brown or blackish spot at the base of the posteriormost dorsal rays, which distinguishes it from  the S. lividus, where the spot is diffuse. When males are in courtship or guarding their eggs they have a broad white bar across the middle of the body and a pale blue stripe from the mouth to the upper part of the pectoral fin.

Living areas
S. nigricans are found naturally in and around coral reefs. Adult S. nigricans live in reef flats and lagoon reefs in colonies in areas with staghorn coral. S. nigricans are limited by water temperature and their diet and have been experiencing a negative impact of their population amounts. Climate and ocean composition has been changing due to global warming and fossil fuel use, therefore this habitat is being altered and coral reefs are becoming greatly reduced.iNaturalist. 2017. “Dusky Damselfish (Stegastes Nigricans).” INaturalist.org, www.inaturalist.org/taxa/49922-Stegastes-nigricans.

S. nigricans is most frequently found across the coast of East Africa and around Madagascar; in the British Indian Ocean Territory and the southern coasts of India; across Southeast Asia, the northern coast of Australia; and Melanesia, Micronesia and Polynesia. They can also be found less frequently in the Red Sea, the Persian Gulf, the Gulf of California, and across the Western coast of Central America.

Biology
Adults inhabit reef flats and lagoon reefs. They often occur in groups associated with live or dead branching staghorn coral (Acropora). They feed on algae, gastropods, sponges and copepods. They are territorial, and they maintain and "weed" filamentous algae patches growing on dead coral. They attack human intruders without hesitation, sometimes taking painful nips.

S. nigricans are oviparous and follow a breeding pair relationship between males and females. Their eggs are sticky and adhere to the coral. Males guard and tend to the egg nest via waving air over them and will be visited by several females throughout their time there. They're particularly aggressive during reproductive periods. During aggressive encounters, they emit clicking noises. Males guard and tend the nest, visited by several females.

References 

nigricans
Category:Fish of the Indian Ocean
Category:Fish of the Pacific Ocean
Category:Taxa described in 1985