Gem Tang (Zebrasoma gemmatum) Care Guide
Zebrasoma gemmatum, the gem tang, is a rare deep-water surgeonfish from the southwestern Indian Ocean, dark brown with numerous white spots and a yellow tail.
Compiled by Aquairi from published sources · Published · Updated
Overview
Zebrasoma gemmatum, the gem tang, is a surgeonfish of the family Acanthuridae. Its body is dark brown with numerous small white spots over the head, body and fins, and the caudal fin is yellow. It is a rare, territorial species and one of the most valuable tangs in the aquarium trade.
Taxonomy
- Family: Acanthuridae
- Genus: Zebrasoma
- Scientific name: Zebrasoma gemmatum
Habitat
The species is endemic to the southwestern Indian Ocean off South Africa, Mozambique, Madagascar, Reunion and Mauritius. It is a deeper-water reef fish, typically found singly below 25 m and down to around 60 m.
Tank requirements
- Minimum tank volume: 600 L
- Temperature: 24-26 °C (75-79 °F)
- pH: 8.1-8.4
- Specific gravity: 1.024-1.026
- Carbonate hardness (dKH): 8-12
- Water flow: high
- Adult size: up to about 22 cm
- Lifespan: 10-25 years
Diet
FishBase gives a trophic level of 2.0, consistent with an algae-based herbivorous diet typical of tangs. In the aquarium it requires plentiful algae or dried marine algae offered several times daily.
Compatibility
Described as extremely territorial and solitary, showing aggression toward conspecifics and other fish. It can be kept with wrasses, clownfish, angelfish and sturdy triggers. Other tangs, especially those of similar shape, should be avoided in smaller tanks.
Reef compatibility
The gem tang is reef-safe and grazes algae. Given its territorial nature and adult size, it needs a spacious reef aquarium with strong flow.
Breeding
Aquarium breeding is not established and is considered an expert undertaking.
Gem Tang Breeding Guide
Overview
Zebrasoma gemmatum, the gem tang, is a western Indian Ocean surgeonfish of Mozambique, South Africa, Madagascar, Reunion and Mauritius, reaching about 22 cm. It is herbivorous, with a low trophic level reflecting a plant-based diet, and is territorial and largely solitary on coral and rocky reefs. As an acanthurid it reproduces by pelagic broadcast spawning. IUCN status is Data Deficient.
Sexing
This species shows no reliable external sexual difference, and its striking spotted pattern does not distinguish the sexes. As in other surgeonfish, sex is apparent only through spawning behaviour, when fish pair or group and rise to release gametes, so deliberate sexing is not practical for aquarists.
Conditioning
Being herbivorous, the gem tang requires constant access to marine algae and frequent feeding to stay in good condition. Given its solitary and territorial nature, holding more than one in the same system to attempt pairing demands a very large, well-structured tank, and stable warm reef water throughout.
Breeding Setup
As a broadcast spawner the gem tang releases eggs into open water, so reproduction relies on water-column space rather than any nest. No aquarium breeding setup has been documented for this rare species, so the description here reflects the general acanthurid pattern rather than a proven home method.
Spawning Behavior & Trigger
Surgeonfish spawn by ascending in the water column, where pairs or groups release eggs and sperm for external fertilisation, and the eggs disperse as plankton. No species-specific captive spawning trigger is documented for the gem tang.
Egg & Fry Care
There is no parental care; the pelagic eggs drift and hatch into the transparent acronurus larva typical of the family, which spends an extended period in open water before settling and metamorphosing. Sustaining this larval stage requires specialised culture conditions not available in a home aquarium.
Common Challenges
Beyond the general difficulty of rearing the long-lived acronurus larva, the gem tang is rare and high-value in the trade and is rarely kept in groups, so even initiating spawning is unlikely in private systems. Only a few surgeonfish, beginning with the yellow tang, have been raised to settlement at all, and the gem tang is not among them.