genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
ray-finned fish
Actinopterygii (; ), members of which are known as ray-finned fishes, is a class of bony fish. They comprise over 50% of living vertebrate species.
The ray-finned fishes are so called because their fins are webs of skin supported by bony or h ...
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 .
Members of this genus are deep-bodied and laterally flattened fish with forked tails. The head has a blunt snout, a small, terminal mouth, a nostril on each side of the face, and large eyes. The lateral line does not run the full length of the body and has gaps in it. A single large dorsal fin is present and the anal fin has two, or rarely three, spines. The colour varies with the species and sometimes varies in different parts of the fish's range. Juvenile fish tend to have bright colours which are completely different from the appearance of adults of that species.
Behaviour
These damselfish feed on
filamentous algae
Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular micr ...
which make up about 90% of their diet, although they may consume detritus and some
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 ...
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
Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a crucia ...
. 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.
Stegastes fasciolatus
''Stegastes fasciolatus'', commonly called the Pacific gregory, is a species of damselfish in the family Pomacentridae. It is native to the tropical western Indo-Pacific. It feeds on filamentous algae.
Distribution and habitat
''Stegastes fasci ...
Stegastes lividus
''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 ...
'' (Forster in Bloch and Schneider, 1801)
*'' Stegastes lubbocki'' Allen and Smith, 1992
*''
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 ...
Stegastes otophorus
''Stegastes'' is a genus of Actinopterygii, 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 damse ...
Stegastes planifrons
''Stegastes planifrons'' (threespot damselfish) is a damselfish from the Western Atlantic. It occasionally makes its way into the aquarium trade.
Description
The adult threespot damselfish is a brownish-grey, bony fish with a dusky yellow sheen ...