Pseudanthias pleurotaenia (Squarespot Anthias / Squareback Anthias)
• Small fish safe: ✅ Yes
• Small invert safe: ✅ Yes
• Coral safe: ✅ Yes
• Minimum tank size: 380L+ (preferably larger for groups)
• Adult size: ~20 cm (8 inches)
• Diet: Carnivorous (zooplankton, frozen mysis/brine shrimp, enriched flake foods)
• Be aware of: One of the largest anthias species—requires a spacious tank. Best kept in harems (one male with multiple females). Can become aggressive towards other anthias species. Requires frequent feedings due to high metabolism.
Squarespot Anthias (Pseudanthias pleurotaenia) – A Stunning and Bold Reef Fish
The Squarespot Anthias, also known as the Squareback Anthias, is a strikingly large and vibrant species known for its bold coloration and active schooling behavior. Unlike smaller anthias, P. pleurotaenia grows significantly larger, making it a dominant presence in larger reef aquariums.
Appearance and Coloration
The Squarespot Anthias is easily recognizable due to its:
• Deep pink to reddish-orange body, creating a rich contrast in reef tanks.
• Males displaying a large purplish square-shaped marking on the mid-body, which intensifies during courtship.
• Bright red stripe running from the snout through the eye, extending along the body.
• Females exhibiting a more yellowish-pink coloration, lacking the distinct square marking.
This dramatic color difference between males and females makes the species particularly eye-catching in mixed harems.
Natural Habitat and Behaviour
Native to the Indo-Pacific, including Indonesia, the Philippines, and Fiji, Squarespot Anthias inhabit:
• Deep coral reef slopes, usually at depths of 10 to 40 meters (30 to 130 feet).
• Large aggregations, where they hover above reef structures, feeding on passing zooplankton.
• Haremic social structures, consisting of one dominant male and multiple females.
• Territorial tendencies, particularly among males establishing dominance.
In captivity, they thrive in well-structured aquariums with open swimming space and strong water movement.
Tank Requirements and Water Parameters
Due to their larger size and active swimming behavior, Squarespot Anthias require a spacious tank with stable water conditions.
• Minimum tank size: 380L+ (100 gallons) for a single individual; larger tanks (500L+) recommended for harems.
• Temperature: 24–27°C (75–81°F)
• pH: 8.1–8.4
• Salinity: 1.020–1.025
• Water movement: Moderate to strong, simulating natural reef currents.
• Aquascaping: Provide ample live rock formations, with caves and ledges for shelter, but maintain open water areasfor swimming.
⚠ Ensure a well-oxygenated environment, as Squarespot Anthias are highly active and require strong circulation.
Diet and Feeding
Squarespot Anthias are planktivores, requiring frequent small feedings to sustain their high metabolic rate. Their ideal diet includes:
• Frozen mysis and brine shrimp – Essential protein sources.
• Enriched frozen plankton – Helps mimic their natural diet.
• High-quality marine pellets and flakes – Supplemented with vitamins and color-enhancers.
• Live foods (copepods, amphipods, rotifers) – Beneficial but not essential.
Feeding frequency: At least 3 times per day to maintain their health and vibrant coloration.
Compatibility and Tank Mates
Squarespot Anthias are larger and more dominant than most anthias species, making them better suited for spacious reef tanks.
✔ Compatible with:
• Other semi-aggressive reef fish, such as Tangs, Large Wrasses, and Rabbitfish.
• Peaceful reef inhabitants, as long as they are not outcompeted for food.
• Reef-safe invertebrates, such as shrimp, snails, and crabs.
❌ Avoid housing with:
• Smaller, timid fish, which may be bullied or outcompeted for food.
• Other large anthias species, which may compete for dominance.
• Aggressive predators, such as Groupers or large Triggerfish.
⚠ If keeping multiple Squarespot Anthias, introduce them at the same time to establish a stable hierarchy.
Behavior and Social Structure
Unlike smaller anthias species, Squarespot Anthias:
• Are more dominant and territorial, especially males defending harems.
• Need ample space to prevent aggression, as confined conditions may lead to fights.
• Exhibit natural dominance hierarchies, where the largest female may transition to male if the dominant male is lost.
Their larger size and bold personality make them one of the most striking anthias species in the hobby.
Health and Disease Considerations
Squarespot Anthias are relatively hardy, but they can be susceptible to:
• Marine Ich (Cryptocaryon irritans) – Particularly if stressed or housed in crowded conditions.
• Bacterial infections, usually caused by territorial disputes or poor water quality.
• Nutritional deficiencies, if not fed a varied diet.
To keep them healthy:
✔ Provide multiple daily feedings to prevent malnutrition.
✔ Ensure ample swimming space to reduce stress.
✔ Maintain stable water conditions with excellent filtration and regular water changes.
Lifespan and Long-Term Care
With proper care, Squarespot Anthias can live up to 5-7 years in captivity. Their large size, vibrant coloration, and active swimming behavior make them a fascinating species for large reef tanks.
Why Choose a Squarespot Anthias?
✔ One of the largest anthias species, making it a dominant display fish.
✔ Bold, vivid coloration, with a unique square marking on males.
✔ Active and engaging, constantly patrolling the tank.
✔ Reef-safe, with no risk to corals or invertebrates.
✔ Fascinating social structure, providing dynamic interactions.
⚠ Important Considerations Before Buying a Squarespot Anthias:
🚫 Requires a large tank, unsuitable for nano or mid-sized setups.
🚫 Best kept in harems, needing a group structure for natural behavior.
🚫 Can become aggressive towards smaller or similar species.
🚫 Needs frequent feedings, which may not suit all aquarists.