''Stegastes fuscus'', the dusky damselfish, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of bony fish in the

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Pomacentridae Pomacentridae is a family of ray-finned fish, comprising the damselfishes and clownfishes. This family were formerly placed in the order Perciformes but are now regarded as being ''incertae sedis'' in the subseries Ovalentaria in the clade Perco ...

found near the seabed in shallow waters on the western fringes of the

Atlantic Ocean The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the " Old World" of Africa, Europe ...

.''Stegastes fuscus'' (Cuvier, 1830)
FishBase. Retrieved 2011-12-29.

Description

The colour of an adult dusky damselfish varies from brownish-olive to dark grey, with fine, darker-coloured, vertical stripes on the body. The fins are large with sometimes a blue rim around the edge of the dorsal and anal fins. The dorsal fin has 12 spines and 15-16 soft rays while the anal fin has two spines and 13-14 soft rays. The dusky damselfish can be distinguished from the very similar longfin damselfish (''

Stegastes diencaeus ''Stegastes diencaeus'', the longfin damselfish, is a damselfish in the family Pomacentridae from the Western Atlantic. It occasionally makes its way into the aquarium trade. It grows to a size of 12.5 cm in length. Longfin damselfish have b ...

'') by the shorter, less angular dorsal and anal fins. The maximum length is , but is a more typical length.Territorial Behavior of the Dusky Damselfish, ''Stegastes fuscus'', at Champagne Reef
Michael Wachter. Retrieved 2011-12-29. The juvenile dusky damselfish is pearly grey with blue spots on the top of its head. It has a large, blue-rimmed, black eyespot where the dorsal fin spines meet the dorsal fin soft rays, and a smaller, similarly coloured eyespot on the caudal peduncle. Some juveniles off the coast of southeastern Brazil have a vivid yellow and orange band on the back and dorsal fin.

Distribution

''Stegastes fuscus'' occurs in shallow waters off Brazil, where it is common on both rocky and

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. Co ...

s at depths down to . It is also reported from the

Caribbean Sea The Caribbean Sea ( es, Mar Caribe; french: Mer des Caraïbes; ht, Lanmè Karayib; jam, Kiaribiyan Sii; nl, Caraïbische Zee; pap, Laman Karibe) is a sea of the Atlantic Ocean in the tropics of the Western Hemisphere. It is bounded by Mexico ...

, but another species, '' Pomacentrus dorsopunicans'', possibly was misidentified there. Another population is reported from

Senegal Senegal,; Wolof: ''Senegaal''; Pulaar: 𞤅𞤫𞤲𞤫𞤺𞤢𞥄𞤤𞤭 (Senegaali); Arabic: السنغال ''As-Sinighal'') officially the Republic of Senegal,; Wolof: ''Réewum Senegaal''; Pulaar : 𞤈𞤫𞤲𞤣𞤢𞥄𞤲𞤣𞤭 � ...

, but this lacks confirmation.

Biology

About 70% of the food consumed by the dusky damselfish consists of algae, mostly red, filamentous algae, but some calcareous algae are also eaten. The rest of their diet is small

invertebrate Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

s. The feeding activities of the damselfish prevent coarser seaweeds, such as '' Jania'' spp., becoming dominant and greatly influences the structure of the benthic community.

Behaviour

The dusky damselfish is a

territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...

species. It guards part of the seabed and repels intruders, sometimes chasing away fish several times its own size.Territorial Habits of ''Stegastes fuscus''
Megan Pugh. Retrieved 2011-12-30. The richer the site was in suitable algae for feeding, the more aggressive the fish became. Besides members of its own species, the main species chased away were

parrotfish Parrotfishes are a group of about 90 fish species regarded as a Family (biology), family (Scaridae), or a subfamily (Scarinae) of the wrasses. With about 95 species, this group's largest species richness is in the Indo-Pacific. They are found ...

, bluehead wrasse (''

Thalassoma bifasciatum ''Thalassoma bifasciatum'', the bluehead, bluehead wrasse or blue-headed wrasse, is a species of marine ray-finned fish, a wrasse from the family Labridae. It is native to the coral reefs of the tropical waters of the western Atlantic Ocean. ...

''), bicolour damselfish (''

Stegastes partitus ''Stegastes partitus'' or the bicolor damselfish is a species of bony fish in the family Pomacentridae found near the sea bed on shallow rocky and coral reefs in the Caribbean Sea, the Gulf of Mexico and off the coasts of Florida.

'') and

ocean surgeonfish The ocean surgeon or ocean surgeonfish (''Acanthurus bahianus'') is a tropical fish known to live in reefs in the western Atlantic Ocean, especially the Caribbean Sea. It is sometimes marketed fresh as a food item,Baensch, H.A. and H. Debelius (1 ...

(''Acanthurus bahianus''). Certain other fish species, such as the smooth trunkfish (''

Rhinesomus triqueter ''Lactophrys triqueter'' also known as the smooth trunkfish, is a species of boxfish found on and near reefs in the Caribbean Sea, Gulf of Mexico and subtropical parts of the western Atlantic Ocean.Matsuura, K. (2014): Taxonomy and systematics of ...

'') and the

graysby The graysby (''Cephalopholis cruentata'') is a species of marine ray-finned fish, a grouper from the subfamily Epinephelinae which is in the family Serranidae which also includes the anthias and sea basses. It is found in the western Atlantic. It ...

(''Cephalopholis cruentata''), were not chased away. The author of the study surmised it was the food source rather than the geographical area being guarded, and these fish were not considered to be threats because they did not graze algae, instead feeding on small invertebrates. An alternative possibility was these fish benefited the dusky damselfish in some other way, such as by providing some protection against

predators Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the ...

or by removing invertebrates that feed on algae.

References

{{Taxonbar, from=Q2196282 fuscus Fish described in 1830 Taxa named by Georges Cuvier