Description:

The Orange Shoulder Tang (Acanthurus olivaceus), also known as the Orangebar Surgeonfish, Orange Spot Surgeonfish, or Olive Tang, is a striking and popular species in the marine aquarium hobby. It undergoes a dramatic colour change from its juvenile to adult phase, making it a fascinating fish to observe.

Here’s a comprehensive care guide for the Orange Shoulder Tang:

Appearance:

• Juvenile: Bright yellow body with a small, subtle orange spot just behind the gill plate. They are often quite peaceful at this stage.
• Adult: The body transforms into a beautiful mix of shades. The front half of the body becomes a light gray or beige, sometimes with a bluish tint, while the rear half turns a darker grayish-brown. The signature orange “shoulder” or “epaulette” becomes very prominent, often edged with deep blue or purple, contrasting sharply with the body color. The caudal (tail) fin is typically dark, and the caudal peduncle (tail base) usually has bright blue spots surrounding the scalpel.
• Caudal Spine: Like all surgeonfish, they possess a sharp, scalpel-like spine on each side of their caudal peduncle, used for defense.

Adult Size:

• Orange Shoulder Tangs are large fish. They typically reach an adult size of 10 to 14 inches (25-35 cm) in captivity. Some individuals may even exceed this size.

Natural Habitat and Distribution:

• Found throughout the Indo-Pacific region, from Christmas Island and the Eastern Indian Ocean to Hawaii and southern Japan, extending south to Lord Howe and Rapa islands (which includes waters around Australia, relevant for Caboolture).
• Juveniles are often found in shallower bays and lagoons, while adults migrate to the highly oxygenated waters on or near the surge zones of the reef.
• They are primarily grazers of coarse, filamentous algae and detritus.

Aquarium Care (Moderate to Advanced):

• Minimum Tank Size: Due to their large adult size and active swimming nature, a minimum of 125-180 gallons (approximately 473-680 liters) is recommended for a single adult Orange Shoulder Tang. Many experienced aquarists advocate for 200-250 gallons or more to truly allow them to thrive and prevent stunting and stress, especially in a community tank. They are constant swimmers and need ample open space.
• Water Parameters: Maintaining pristine and highly stable water quality is crucial.
  • Temperature: 75-82F (24-28C)
  • Salinity: 1.020-1.025 specific gravity
  • pH: 8.1-8.4
  • Alkalinity (dKH): 8-12 dKH
  • Ammonia and nitrites must be 0 ppm. Nitrates should be kept as low as possible, ideally below 10-20 ppm.
• Filtration: A robust and efficient filtration system, including a strong protein skimmer, is essential to handle their significant bio-load and maintain water quality.
• Water Flow: They require strong water flow and good circulation to mimic their natural habitat. Powerheads and wavemakers are highly recommended.
• Diet:
  • Herbivorous (primarily): Their diet should be rich in marine-based algae and seaweed. They are excellent grazers on natural algae in the tank.
  • Offer dried seaweed (nori) tied to a rock or using a veggie clip several times a week (at least 3-4 times, ideally daily).
  • Supplement with high-quality herbivore pellets and flakes (e.g., Spirulina-rich foods), and other vegetable matter (e.g., blanched zucchini, broccoli).
  • They are technically omnivores and will accept meaty foods like mysis shrimp or brine shrimp, but these should be offered sparingly as treats and not form the bulk of their diet.
  • Frequent small feedings (2-3 times a day) are best to support their active metabolism and grazing habits. A well-fed tang is less prone to aggression and diseases like HLLE (Head and Lateral Line Erosion).
• Temperament:
  • Juveniles: Generally quite peaceful towards other fish species.
  • Adults: Can become territorial and semi-aggressive, particularly towards other tangs, especially those of similar body shape (e.g., other Acanthurus species) or coloration.
  • It is generally recommended to keep only one Orange Shoulder Tang per tank. If attempting to keep multiple tangs in a very large system, they should be introduced simultaneously and ideally be of different genera and body shapes. Adding the Orange Shoulder Tang as one of the last fish (or at the same time as other tangs) can sometimes help mitigate aggression.
  • They are generally peaceful towards other non-tang species.
• Reef Compatibility: Generally considered reef safe. They primarily graze on algae and are unlikely to bother corals or most invertebrates, making them a suitable addition to a mixed reef tank, provided their other needs (tank size, aggression) are met. They are excellent for natural algae control.
• Tank Setup:
  • Provide plenty of live rock to allow for natural grazing and offer hiding places and territories.
  • Crucially, ensure ample open swimming areas in the water column.
  • A well-established aquarium (at least 6 months to a year old) with stable water parameters is highly recommended before introducing this fish.
  • A secure, tight-fitting lid is essential as they are powerful jumpers, especially when startled.
• Disease Susceptibility: Like most tangs, they can be susceptible to marine ich (Cryptocaryon irritans) and other parasitic infections if stressed or in poor water quality. Maintaining pristine conditions and providing a varied, nutrient-rich diet (especially with garlic supplements) helps boost their immune system.
• Acclimation: Proper and slow acclimation (drip acclimation) is absolutely essential due to their sensitivity to changes in water chemistry.