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Stegastes nigricans, commonly known as the Dusky Gregory, is a species of damselfish found in tropical Indo-Pacific waters. It is a highly territorial and aggressive fish, particularly towards conspecifics and other herbivorous fish, playing a significant role in shaping algal communities on coral reefs. Its robust body and distinctive coloration make it easily recognizable.
Physical Characteristics
- Body shape
- compressed
- Coloration
- Adults are typically dark brown to black, often with a yellowish or pale caudal fin, especially in juveniles and subadults. Some individuals may exhibit a pale bar or patch on the flank. The intensity of coloration can vary with mood and environment.
- Scale type
- ctenoid
- Mouth position
- terminal
- Distinctive features
- Robust, deep body, Small, terminal mouth, Prominent eyes, Often a pale or yellowish caudal fin, particularly in younger individuals, Dark spot at the base of the pectoral fin
- Dorsal fin
- Single dorsal fin with 12 spines and 15-17 soft rays. The spiny and soft-rayed portions are continuous.
- Tail fin
- Forked or emarginate caudal fin, often yellowish.
- Pectoral fin
- Well-developed pectoral fins, typically clear or slightly dusky.
- Distinctive fins
- Anal fin with 2 spines and 12-14 soft rays. Pelvic fins are thoracic.
Identification Tips
Coloration
Look for the overall dark brown to black body, often with a contrasting yellowish or pale caudal fin, especially in juveniles. The dark spot at the pectoral fin base is also a good indicator.
Body Shape
Its deep, compressed body is characteristic of damselfishes, but its robust build helps distinguish it from more slender species.
Behavior
Observe its highly territorial behavior, aggressively defending a patch of algae from other fish. This behavior is a strong clue to its identity.
Habitat
Its strong association with live coral and rocky substrates in shallow reef environments is a key identification aid.
Habitat
- Water type
- saltwater
- Depth
- Typically found in shallow waters from 0.5 to 12 meters (1.6 to 39 feet), occasionally deeper.
- Environment
- Coral reefs, rocky intertidal zones, and rubble areas. Strongly associated with live coral, particularly branching corals, which they use for shelter and as a substrate for their algal gardens. They are highly territorial and defend their patches of algae.
- Geographic range
- Widespread throughout the Indo-Pacific region, from the Red Sea and East Africa across to the Central Pacific, including Hawaii, and south to Australia and New Caledonia.
Aquarium Information
- Care level: intermediate
- Temperament: aggressive
- Diet: omnivore
- Minimum tank size: 50 gallons
- Temperature: 24-28°C (75-82°F)
- pH level: 8.1-8.4
- Hardness: 8-12 dKH
- Compatibility: Not suitable for community tanks with smaller, peaceful fish. Can be kept with larger, robust, and equally aggressive species. Best kept singly or in very large tanks with ample territory.
- Special requirements: Requires abundant rockwork and crevices for shelter and territory establishment. A well-established tank with mature live rock is crucial. Provide a varied diet including spirulina, marine algae, and meaty foods. Due to its aggressive nature, careful tankmate selection is paramount.
Wild Information
- Conservation status: least concern
- Seasonality: Breeds year-round in tropical waters, with peak activity often influenced by lunar cycles and water temperature.
- Market price: Low
- Commercial importance: low
- Taste: Not commonly consumed due to small size and bony nature.
- Texture: Not applicable for culinary purposes.
- Nutritional value: Not applicable for culinary purposes.
Key Facts
Algal Farmerbehavior
Stegastes nigricans is a well-known 'algal farmer'. It actively cultivates and defends patches of filamentous algae, removing undesirable species and aggressively chasing away other herbivores that attempt to graze on its garden.
Territorial Championbehavior
This species is one of the most territorial damselfishes. Its aggressive defense of its algal patch is crucial for its survival and significantly impacts the local reef ecology by maintaining specific algal communities.
Reef Ecosystem Engineerinteresting
By maintaining its algal gardens, the Dusky Gregory acts as an ecosystem engineer, influencing the distribution and abundance of algae and, consequently, the structure of the coral reef community.
Juvenile Colorationinteresting
Juvenile Stegastes nigricans often exhibit a more pronounced yellowish caudal fin and sometimes iridescent blue spots on their head and body, which fade as they mature.
Safety Information
Handle with care- Safety level: caution
- Venomous: No
- Edibility: not recommended
- Handling notes: While not venomous, Stegastes nigricans can deliver a painful bite if handled carelessly, especially larger individuals. Their dorsal and anal fin spines are sharp and can cause punctures. Exercise caution when handling to avoid injury. They are also highly aggressive and territorial, which can be a concern in aquarium settings.
Similar Species
Blackspot Sergeant
Abudefduf sordidus
While also dark-bodied, Abudefduf sordidus typically has distinct vertical bars and a more elongated body shape. It also lacks the prominent yellowish caudal fin often seen in Stegastes nigricans.
Jewel Damselfish
Plectroglyphidodon dickii
Plectroglyphidodon dickii is generally smaller and possesses a distinct black bar or spot on its side, which is absent in Stegastes nigricans. Its body is also typically less robust.
Other Stegastes species
Various Stegastes spp.
Many Stegastes species share similar body plans. Careful attention to specific color patterns, fin coloration (especially the caudal fin), and the presence or absence of distinct spots or bars is crucial for differentiation. For example, some Stegastes species may have entirely dark caudal fins or different body markings.
Scientific Classification
- Kingdom
- Animalia
- Phylum
- Chordata
- Class
- Actinopterygii
- Order
- Perciformes
- Family
- Pomacentridae
- Genus
- Stegastes
- Species
- nigricans
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