Overview

Comprehensive Description

The numerous damselfishes of this genus are known for marked coloration and pattern changes as they grow, mostly converging on a uniform dusky appearance as adults. Pre-transitional larval Stegastes are mostly colorless with few distinguishing markings and overlap extensively in meristics and thus DNA sequencing is necessary to identify many larvae to species. Damselfish larvae rapidly acquire juvenile markings during the night of settlement and transitional larvae are common in collections over the reef, even before they have the chance to transform in a trap.

New recruits of some Stegastes species can share the markings that are used as species-specific diagnostic characters in the later juvenile stages. These shared markings include the pattern of spots and stripes on the head, the size, shape, and position of the dorsal-fin ocellus, the spot at the top of the pectoral-fin base, and the upper caudal-peduncle saddle-spot. These characters may not be consistent for identifying juveniles below 20 mm SL and many species identifications of photographs of small juveniles on the web and in reef fish guides are mistaken. Furthermore, the published descriptions of juveniles of this genus are almost always incongruent and depend on highly variable characters, such as shades of yellow or the degree of striping. The most egregious example of this is the commonplace assignment of any juvenile with blue head stripes to S. diencaeus.

Transient ontogenetic homologies in pomacentrid early life history: This interesting phenomenon of short-lived, presumably vestigial, markings that appear on early juveniles is somewhat analogous to the homologies in ontogeny shown in mammalian embryology. In this case, however, ontogeny may recapitulate phylogeny (in a way) as ancestral markings may persist in the earliest juveniles of an entire clade. The similarity may extend to the mechanism for the persistence: just as obsolete embryological structures persist because of reduced selection pressure within the womb (for example the hindlimbs in dolphin embryos), these early markings may persist because of reduced selection pressure for species recognition among the smallest juvenile stages on the reef. Alternatively, a more intriguing explanation may be that this phenomenon is an adaptation to disguise species identity at the time of extreme vulnerability to competitive interactions from adults.

Species Identification: Among the larval Stegastes, S. partitus diverges first during the transition phase by not developing the dorsal-fin ocellus shared by all of the other reef species. The dorsal-fin ocellus is the first transitional marking appearing on larvae. Immediately afterwards, the outlines of iridescent spots and stripes appear on the head and upper body and the spotted species, S. adustus and S. planifrons, can be distinguished from the striped species, S. diencaeus, S. leucostictus, and S. variabilis.

New recruits of S. partitus share the blue spots and stripes on the head characteristic of other Stegastes, although these are usually not conspicuous and disappear rapidly. Once the dorsal-fin ocellus develops, S. adustus and S. planifrons can be distinguished by having only spots, not stripes, on the top of the head (as well as other distinctive color patterns). The three remaining reef species, all with a dorsal-fin ocellus and stripes on the head, share most basic markings as new recruits (S. diencaeus, S. leucostictus, and S. variabilis). Nevertheless, with the characters described below, juveniles of these species should be categorized correctly. It should be noted, however, that intermediate individuals do occur. This is probably variability within species, although the possibility of occasional hybridization should not be excluded. DNA-sequencing analyses, underway at present on this group, will confirm the identification of larvae and new recruits of these species and explore the hybridization question further.

The most troublesome feature of juvenile markings in these damselfishes is the rapid change in the size, shape, and position of the spots, stripes, and the dorsal-fin ocellus. Overlying these ontogenetic changes is a high degree of variability within species. My DNA sequencing of these damselfishes reveals that many features are inconsistent for separating species at these early stages, especially the size and position of the dorsal-fin ocellus and the intensity of spots on the head and dorsal fin.

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Ecology

Habitat

Depth range based on 1182 specimens in 37 taxa.
Water temperature and chemistry ranges based on 784 samples.

Environmental ranges
  Depth range (m): 0 - 200
  Temperature range (°C): 19.490 - 29.336
  Nitrate (umol/L): 0.006 - 9.845
  Salinity (PPS): 32.019 - 37.169
  Oxygen (ml/l): 3.830 - 5.079
  Phosphate (umol/l): 0.046 - 1.385
  Silicate (umol/l): 0.866 - 17.402

Graphical representation

Depth range (m): 0 - 200

Temperature range (°C): 19.490 - 29.336

Nitrate (umol/L): 0.006 - 9.845

Salinity (PPS): 32.019 - 37.169

Oxygen (ml/l): 3.830 - 5.079

Phosphate (umol/l): 0.046 - 1.385

Silicate (umol/l): 0.866 - 17.402
 
Note: this information has not been validated. Check this *note*. Your feedback is most welcome.

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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
Specimen Records:1248
Specimens with Sequences:1162
Specimens with Barcodes:1107
Species:37
Species With Barcodes:34
Public Records:891
Public Species:20
Public BINs:20
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Statistics of barcoding coverage: Stegastes cf. limbatus

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 2
Species With Barcodes: 1
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Barcode data

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Wikipedia

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.[2] 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[edit]

The largest species in the genus is S. acapulcoensis, which grows to a maximum length of 17 cm (7 in), while the smallest is S. pictus at 7.5 cm (3.0 in). [3] 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.[4]

Behaviour[edit]

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.[5] 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.[6]

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.[6]

Captive care[edit]

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.[6]

Species[edit]

The World Register of Marine Species lists these species: [1]

References[edit]

  1. ^ a b WoRMS (2013). "Stegastes Jenyns, 1840". World Register of Marine Species. Retrieved 2014-01-08. 
  2. ^ Froese, Rainer and Pauly, Daniel, eds. (2012). "Stegastes otophorus" in FishBase. June 2012 version.
  3. ^ "Stegastes". FishBase. Retrieved 2014-01-08. 
  4. ^ "Family Pomacentridae - Damselfishes". FishBase. Retrieved 2014-01-08. 
  5. ^ Ferreiraa, Carlos Eduardo L.; Gonçalves, José Eduardo A.; Coutinho, Ricardo; Pereta, Alberto C. (1998). "Herbivory by the Dusky Damselfish Stegastes fuscus (Cuvier, 1830) in a tropical rocky shore: effects on the benthic community". Journal of Experimental Marine Biology and Ecology 229 (2): 241–264. doi:10.1016/S0022-0981(98)00056-2. 
  6. ^ a b c Henry C. Schultz III. "Fish Tales". Reefkeeping. Retrieved 2014-01-08. 
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