Whitecheek surgeonfish

This species is widely distributed across the tropical waters of the Central and Western Pacific Ocean, ranging from southern Japan to Australia and Indonesia, extending east to Hawaii and French Polynesia. It primarily inhabits seaward reef slopes exposed to strong surge, deep drop-offs, and clear lagoons at depths between 1 and 30 meters, actively swimming close to coral structures.

Belonging to the family Acanthuridae, it is also frequently referred to in scientific literature as Acanthurus japonicus. It features an oval, deep, laterally compressed body with a terminal mouth containing small teeth adapted for grazing on algae. Adults reach a maximum total length of approximately 20 centimeters. It features a sharp caudal spine on each side of the peduncle.

It is a highly active, diurnal, and territorial fish. In the wild, it is solitary or forms small grazing aggregations to feed on algal turf. In the aquarium, it exhibits strong territorial aggression toward conspecifics and other similarly shaped surgeonfish, requiring plenty of swimming space and visual barriers to minimize conflict.

The coloration is highly distinct: the body is dark grayish-blue to near-black, with a prominent white crescent-shaped patch below the eye. The dorsal and anal fins feature a bright yellow band along their bases and electric blue edges, while the caudal fin is white with a vertical yellow band. No external sexual dimorphism is visible.

Requires a mature marine aquarium of at least 450-500 liters for a single specimen. The tank should be furnished with a large amount of established live rock to allow for natural grazing on algae, while providing a wide open area for active swimming. High water movement, strong oxygenation, and a robust protein skimmer are essential.

A specialized herbivore feeding on filamentous algae in nature. In captivity, it must be offered a diet rich in vegetable matter, consisting of dried nori sheets, spirulina-rich flakes, and high-quality herbivore pellets. Supplement with frozen foods like mysis and brine shrimp to support its high metabolic rate and prevent weight loss.

Requires stable and pristine water parameters: temperature between 24°C and 26°C, pH range from 8.1 to 8.4, specific gravity (SG) from 1.020 to 1.025, and carbonate hardness (KH) of 8 to 12 dKH. Ammonia and nitrite must be zero, with nitrates kept below 15 ppm through regular water changes and efficient filtration.

Completely reef safe, as it will not harm corals or sessile invertebrates. It coexists peacefully with smaller reef fish like wrasses, anthias, gobies, and clownfish. However, it will exhibit strong territorial behavior toward other Acanthurus species of similar shape (such as Acanthurus leucosternon). Introduce it last to minimize aggression.

Captive breeding in home aquariums has not been achieved. They are broadcast spawners that release pelagic eggs into the water column. The drifting eggs hatch into delicate larvae that drift with ocean currents. Rearing these larvae in closed systems is currently impossible due to their microscopic live food requirements.

Highly susceptible to marine ectoparasites such as Cryptocaryon irritans (marine ich) and Oodinium (velvet) due to a very thin protective mucus layer. It is also prone to Head and Lateral Line Erosion (HLLE) if its diet is deficient in vitamins or if water quality is poor. A strict quarantine period and a UV sterilizer are highly advised.