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Zebrasoma gemmatum

Gem tang

The gem tang, known in Italian as pesce chirurgo mauriziano 4, is a surgeonfish (Acanthuridae) 1 from the south-western Indian Ocean, up to 22 cm long. 2 It is dark brown with small white spots and a yellow tail, 3 very territorial and usually solitary. 2 It usually stays deeper than 25 m. 2

AcanthuridaeIUCN: Data deficient
Zebrasoma gemmatum

At a glance

Data from the scientific sources listed at the bottom.

Depth in the wild

25–61 m

0 m20 m40 m60 m80 m100 m

Size

up to 22 cm

0612182430

maximum total length according to FishBase; the Oregon Coast Aquarium gives 18 cm

Temperature in the wild

24–28 °C

18 °C34 °C

Where it lives

Red SeaWestern Indian OceanEastern Indian OceanCentral Indo-PacificWestern PacificCentral PacificEastern PacificWestern AtlanticEastern AtlanticMediterranean

Mozambique and South Africa, then Madagascar, Réunion and Mauritius. 2 The Oregon Coast Aquarium gives the Natal area for South Africa. 3 The specimen on which the description is based came from Mauritius. 5

Conservation

NEDDLCNTVUENCREWEX

IUCN Red List: data deficient (2010). Red List data taken from FishBase and GBIF. 2 4 It does not appear in the CITES lists checked on Species+. 6 It is subject to commercial fishing and to trade for the aquarium hobby. 2

How to recognise it

Tap a number on the photo: the key explains what to look for.

123
  1. 1White spots small, all over the dark body 3
  2. 2Yellow tail in contrast with the dark brown body 3
  3. 3Spots on the tail the pale spots continue onto the yellow fin 3

Life in the wild

Where it is found

Coral and rocky reefs. 2 The Oregon Coast Aquarium adds lagoons, coral flats, outer slopes and rocky walls. 3 FishBase gives it between 10 and 61 m, usually from 25 m down; juveniles stay in shallow, sheltered water, adults below 20 m. 2 3

What it eats

It eats various algae. 3

Behaviour

Extremely territorial and solitary. 2 3 It has a spine on each side at the base of the tail, which it uses to defend itself from predators, to defend its territory and to assert itself over others. 3

Reproduction

Eggs and sperm are released into open water. Currents carry the eggs and then the larvae, which later settle to the bottom. Males and females look alike. 3

In the aquarium

From the experience of the BallingMania community.

Community rating
Level in the tank
lowmediumhigh
Coral compatibility
lowmediumhigh
Aggression
lowmediumhigh
Care difficulty
lowmediumhigh
Original sheet

A fish belonging to the family Acanthuridae, an animal coming from the south-western Indian Ocean: Mozambique, Madagascar, the Seychelles and Mauritius.

In the wild it lives in the shallow waters of lagoon areas or close to the reef cliff.

It has a round body, strongly compressed laterally; a small, prominent mouth on the lower part of the head.

The livery is very colourful and striking; the base colour is a dark violet covered with lengthwise dashes; the whole body has a dense network of small whitish-yellow dots; the caudal fin is yellow with clearly visible rays.

Like all surgeonfish, on the caudal fin they have the classic "scalpels", very sharp bony structures used to defend themselves from rivals or natural predators.

To keep it in a tank, excellent water quality is needed; in optimal conditions it is an animal resistant to disease, but it suffers from low pH and excessive concentrations of nitrate and phosphate; it loves a strong flow.

When stressed it is prone to attacks of Oodinium and to fungal skin infections. Prone to intestinal parasites and worms.

It can be kept in tanks larger than 300 litres, with adequate room for swimming and crevices among the rocks to take refuge in.

Difficult to settle in because it is very fearful; for this reason it is better to buy specimens already perfectly acclimatised by an expert. Once well settled in it is omnivorous: in fact it accepts frozen food (Artemia, chironomus, mysis, dry foods) and sheets of Nori seaweed. It does not refuse vegetables such as lettuce or boiled spinach.

Like all Acanthurids it is very well suited to a tank with invertebrates; it can be called "reef safe".

Species sheet by Massimo Ramognino and photo by Rocco Parretta

What studies say about keeping it

The Oregon Coast Aquarium, accredited by the AZA, keeps it in its Connected Coasts exhibit, but does not publish husbandry data. 3

Did you know?

The genus name Zebrasoma recalls a zebra's stripes, but this species is spotted, not striped. 2 3
The scientific name began as Acanthurus gemmatus, from a single specimen from Mauritius kept in Paris. 5
By eating algae it helps keep them under control on the reef, to the benefit of the corals. 3

Sources

  1. WoRMS Editorial Board (2026). Zebrasoma gemmatum (Valenciennes, 1835). World Register of Marine Species.
  2. Froese R., Pauly D. (eds.) (2026). Zebrasoma gemmatum, Spotted tang. FishBase.
  3. Oregon Coast Aquarium (2026). Gem Tang, Zebrasoma gemmatum. Oregon Coast Aquarium.
  4. GBIF Secretariat, da Catalogue of Life (2026). Zebrasoma gemmatum, common names and Red List category. GBIF.
  5. Eschmeyer's Catalog of Fishes (2026). Eschmeyer's Catalog of Fishes, genere Zebrasoma. California Academy of Sciences.
  6. UNEP-WCMC, Segretariato CITES (2026). Search for Zebrasoma gemmatum in the CITES lists. Species+.

Sources checked on 5 November 2026. Community texts and ratings are kept separate from the scientific data.

View the original sheet (Italian)All species