Stegastes
Stegastes is a genus of ray-finned fish in the family Pomacentridae. Members of this genus are marine coastal fishes except for "S. otophorus", which also occurs in brackish water. These fish are known by the names of damselfish, gregory and major. They are small tropical fish associated with coral and rocky reefs in the Atlantic, Indian and Pacific Oceans. They are sometimes found in the aquarium trade where they are an easy-to-keep fish, but they do not mix well with other fish of their own or other species because of their territorial habits and aggressiveness. Description . The largest species in the genus is "S. acapulcoensis", which grows to a maximum length of , while the smallest is "S. pictus" at . Behaviour. These damselfish feed on filamentous algae which make up about 90% of their diet, although they may consume detritus and some invertebrate material, possibly ingesting it accidentally with the algae. They are territorial and cultivate the algae, guarding their garden from other fish. Most species of "Stegastes" live a solitary existence, though some live in association with a member of the opposite sex and a few form loose aggregations of a small number of individuals. They  tend not to face too much competition from other fish because of the very shallow water in which they live and because their habitat is not actually on reefs, but is near them, among boulders, dead branching corals, man-made structures, and junk. Most species are very aggressive and attack anything that moves into their territory, including nipping divers to drive them away. Their behaviour changes somewhat during the breeding season. The male prepares a nesting site by cleaning a smooth piece of rock, removing algae and debris, and removing or driving away from the vicinity unwanted invertebrates such as  starfish and sea urchins. He then signals his readiness to breed by changing hue and displaying his brighter colours. A female that accepts his advances lays a single layer of eggs which she attaches to the prepared rock. The male fertilises them and then stays to guard them, removing any debris that lands on them or unfertilised eggs and fanning the developing embryos with his fins to keep them well oxygenated. The eggs hatch in about a week, the larvae drifting away as part of the plankton. About a month later, they settle to the seabed and undergo metamorphosis into  juveniles, well away from the territories occupied by the adults. In the aquarium. "Stegastes" species may be offered to new aquarists on the grounds that they are easy to care for. They will indeed tolerate poor water quality and feed on the algae which is often a nuisance in reef tanks, but because of their aggressive behaviour, they should not be kept with other fish, especially smaller ones. Species. FishBase lists these species: