The fish you're likely referring to as the Gold-Rimmed Surgeonfish is scientifically known as Acanthurus nigricans. It is also commonly called the Whitecheek Tang, Velvet Surgeonfish, or Goldrim Surgeonfish.

Appearance:

• They have a deep blue to purplish-blue body.
• A distinctive white or light blue patch is present on the cheek, just behind the mouth.
• The caudal fin (tail fin) is typically light blue with a yellow vertical bar.
• The dorsal, anal, and pectoral fins are dark blue with brighter blue highlights.
• A yellow stripe often runs along the base of the dorsal and anal fins, sometimes forming a "wishbone" shape towards the tail.

Natural Habitat and Distribution:

• Found throughout the Indo-Pacific region, from the Cocos-Keeling Islands and Christmas Island to Southern Japan, south to the Hawaiian Islands and the Great Barrier Reef.
• Inhabit shallow coastal reefs and lower surge zones, typically at depths of 6 to 200 feet (2 to 60 meters).
• They primarily feed on filamentous algae in the wild.

Aquarium Care:

• Minimum Tank Size: Due to their active swimming habits and potential adult size, a tank of 125 gallons (approximately 473 liters) or larger is strongly recommended. More swimming space is always better.
• Water Parameters:
  • Temperature: 72-78°F (22-26°C)
  • Salinity: 1.020-1.025 specific gravity
  • pH: 8.1-8.4
  • Alkalinity: 8-12 dKH
  • Water Flow: They require strong and turbulent water flow with good oxygenation.
• Diet:
  • They are primarily herbivores and require a diet rich in marine-based algae and seaweed.
  • Offer a variety of dried seaweed (nori) tied to a rock or using a veggie clip several times a week (at least 3 times).
  • Supplement their diet with other vegetable matter like Spirulina, zucchini, broccoli, and leaf lettuce.
  • While they may accept meaty foods, these should only make up a very small portion of their diet.
  • Small meals 3-4 times a day are better than one large feeding.
• Temperament:
  • The Whitecheek Tang is considered semi-aggressive to aggressive, especially towards other tangs or similarly shaped fish.
  • It is generally best to keep only one Whitecheek Tang per tank unless the aquarium is very large (hundreds of gallons) and all tangs are introduced simultaneously.
  • They can be peaceful with other non-tang species.
• Reef Compatibility: Generally considered reef safe, but if not fed adequately, they may nip at large polyp stony (LPS) corals. They will not typically harm invertebrates.
• Tank Setup:
  • Provide plenty of live rock to allow for natural grazing and to offer hiding places.
  • Ensure open swimming areas are available.
  • A well-established aquarium with stable water parameters is crucial. It's best to introduce them to tanks that are at least a year old.
• Care Level: Considered intermediate to advanced due to their specific needs and potential for aggression and susceptibility to diseases like marine ich if water quality is poor or unstable.
• Acclimation: Proper and slow acclimation (drip acclimation) is essential due to their sensitivity to changes in water chemistry.

Important Considerations:

• Quarantine: It is highly recommended to quarantine new arrivals before introducing them to the main tank to prevent the spread of disease.
• Observation: Closely observe your Gold-Rimmed Surgeonfish, especially during the initial weeks, to ensure they are eating well and adjusting to their new environment.
• Water Quality: Maintaining pristine and stable water quality is paramount for their long-term health.

By providing the appropriate environment, diet, and care, you can successfully keep a Gold-Rimmed Surgeonfish (Whitecheek Tang) in your marine aquarium. However, be prepared for their potential for aggression and ensure your tank is large enough to accommodate their needs.