Acanthurus sohal

Native to the Red Sea, the Sohal Surgeonfish is a very active and territorial herbivore that requires a substantial aquarium with a strong water current to thrive. This fish is known for its constant swimming and its need for a large amount of open space to patrol. As a dedicated herbivore, its diet should primarily consist of marine-based algae and vegetables, which should be offered several times throughout the day to accommodate its high metabolism. Due to its significant dietary needs and active nature, it produces a considerable amount of waste, making a powerful filtration system essential to maintain water quality.

This species is notably territorial, especially towards other tangs, and is best kept as the solitary centerpiece fish in a saltwater aquarium. It demands pristine and stable water conditions, including warm tropical temperatures and a consistent alkaline pH. Given its large adult size, specific environmental needs, and challenging temperament, it is recommended only for experienced aquarists who can provide a very large and appropriately equipped marine system. With proper care, this fish can be a long-lived and impressive inhabitant of a home aquarium.

The Sohal Surgeonfish is a demanding but rewarding species for the advanced marine aquarist with a suitably large system. Originating from the high-energy reef environments of the Red Sea, its captive requirements directly reflect its natural habitat. It requires an exceptionally large aquarium not only to accommodate its significant adult size but also to provide the expansive swimming area it needs. In the wild, this fish patrols a large territory, and this innate behavior translates to constant, energetic activity in an aquarium. To replicate its natural environment, one must generate strong, consistent water flow throughout the entire tank. This vigorous circulation is crucial for promoting gas exchange to meet the fish's high oxygen demands and for keeping detritus suspended for removal by filtration.

Physiologically, this species has a high metabolic rate, which dictates several key aspects of its care. It must be fed multiple times per day to sustain its energy levels. A diet rich in marine-based macroalgae is essential for its long-term health, helping to prevent common ailments and reduce aggression. This can be supplemented with high-quality flakes, pellets, and frozen foods designed for herbivores. A direct consequence of this high metabolism and frequent feeding is substantial waste production. Therefore, an oversized and highly efficient filtration system, including a powerful protein skimmer, is not a luxury but a necessity to manage the high bioload and maintain pristine, stable water parameters. Regular, large-volume water changes are also critical.

Behaviorally, this fish is famously territorial and aggressive. It will typically not tolerate any other surgeonfish in the same aquarium, especially those of a similar shape or from the same genus. It is best housed as the only tang in the tank. Any tank mates must be chosen with extreme care; they should be robust and large enough not to be bullied, yet not so aggressive as to challenge the tang for dominance. Due to these complex requirements—spanning tank size, equipment, diet, and social dynamics—this species is considered difficult to keep and is only suited for seasoned hobbyists dedicated to building a system around its specific needs.

As a member of the family Acanthuridae, Acanthurus sohal exhibits the key characteristics of its genus, including a laterally compressed, or compressiform, body shape designed for agility and speed around reef structures. A defining morphological feature is the presence of a scalpel-like spine on the caudal peduncle, which is used for defense against predators and for intraspecific combat to establish dominance over territory and resources. Native exclusively to the Red Sea and its surrounding waters, this species occupies a specific ecological niche as a diurnal herbivore.

Its role in the ecosystem is primarily that of a grazer, controlling the growth of algae on reef flats and crests. This constant foraging behavior is linked to its high metabolic rate and correspondingly high oxygen consumption. In a closed aquarium system, these physiological traits necessitate an environment with high levels of dissolved oxygen, typically achieved through vigorous surface agitation and strong, laminar water flow. The species' high rate of metabolism also results in significant nitrogenous waste production, contributing a substantial bioload to the aquatic environment. A proper captive setup must account for this with advanced filtration methods to prevent the accumulation of toxins and maintain stable water chemistry within a narrow alkaline range.

Its social structure in the wild is typically solitary or in pairs, with individuals aggressively defending feeding territories. This innate territoriality is a primary consideration for captive husbandry, as the fish will display extreme aggression towards conspecifics and other tangs. From a conservation standpoint, Acanthurus sohal is currently listed as a species of Least Concern by the IUCN, indicating a stable wild population. However, like many popular marine ornamentals, it is subject to collection pressures for the aquarium trade.

The captive breeding of the Sohal Surgeonfish is not a feasible goal for a home aquarist and has not been successfully documented in the hobby. All individuals in the aquarium trade are collected from the wild. The primary obstacle to captive reproduction lies in their natural reproductive strategy as broadcast spawners.

In their natural Red Sea habitat, these fish engage in group spawning events, where they release gametes directly into the water column. This process is synchronized by complex environmental triggers, such as lunar cycles, specific water temperatures, tides, and social cues from a large population, which are nearly impossible to replicate in a closed aquarium system. The social dynamics and courtship rituals leading to spawning require vast open-water territories and vertical space for spawning ascents that far exceed the dimensions of even the largest private aquariums. Furthermore, there is no discernible sexual dimorphism, making it impossible for an aquarist to distinguish males from females to even attempt to form a pair.

Even if spawning could be induced, the subsequent larval stage presents an even greater challenge. The pelagic larvae are exceptionally small and have a prolonged development phase in the open ocean. During this time, they require a continuous supply of specific, microscopic planktonic foods of the right type and density. The science and technology required to raise such delicate larvae are highly specialized and largely confined to commercial aquaculture facilities, which have only recently had limited success with some other surgeonfish species. Therefore, hobbyist efforts should be directed entirely toward providing the best possible long-term care and environment for a single individual, rather than pursuing the unattainable goal of breeding.