The Gem Tang (Zebrasoma gemmatum) is a surgeonfish native to the western Indian Ocean, including Mauritius, Réunion, Rodrigues, Madagascar, and the coast of South Africa. It is also known as the Jewelled Tang, Spotted Tang, and Mauritian Tang.
Appearance
Gem Tangs have a dark, almost black body covered in small white or blue-white spots that extend across the fins. Their body shape is typical of the Zebrasoma genus, with a rounded body, narrow snout, and a distinct white tail spine. Adults reach roughly 8 inches in length, while juveniles show sharper contrast and tighter spotting patterns.
Behavior and Daily Activity
Gem Tangs spend much of the day grazing and moving steadily across rock surfaces. They travel quickly, weaving through narrow gaps while covering a wide foraging area. Gem Tangs usually maintain a personal territory and may show brief chases or displays when other herbivorous fish enter that space. Outside of these moments, they follow a consistent routine centered around feeding.
Feeding Habits
Gem Tangs are primarily herbivores. Their diet consists mainly of filamentous and film algae, which they pick from rock surfaces throughout the day. Their digestive system is adapted for a steady intake of algae. While they may consume small amounts of other organic matter while grazing, algae form the majority of what they naturally eat.
Reef Safety
Gem Tangs are widely regarded as reef-safe. Their grazing behavior focuses on algae and does not typically involve corals, clams, or other sessile invertebrates. They may help reduce algal buildup on rock surfaces, and interactions with coral tissue are uncommon unless a coral is already weakened.
Compatibility With Other Species
Gem Tangs usually coexist peacefully with species that do not share their grazing niche. Territorial behavior is most commonly seen toward similarly shaped or similarly feeding fish, especially other Zebrasoma tangs. They tend to ignore species that occupy different roles on the reef and remain focused on their own feeding patterns.
