Squareback Anthias: The Squarespot Flasher

The Squareback Anthias (Pseudanthias pleurotaenia), also known as the Squarespot Anthias, Pink Square Anthias, or Mirror Basslet, is a popular, large, and vividly colored member of the Anthiinae subfamily. Like all Anthias, they are protogynous hermaphrodites, meaning all individuals are born female and the most dominant female in a social group will change into a male if one is needed.

Native to the deep outer reef slopes and drop-offs of the Indo-West Pacific, this anthias is found in areas with strong currents, often in large, active schools. Its social structure requires it to be kept in a harem—ideally one male with three to six females—to distribute aggression and encourage natural behavior.

The Squareback Anthias is an active, mid-water planktivore, requiring a high level of care due to its fast metabolism (requiring multiple daily feedings) and need for stable, pristine water quality. A secure, tight-fitting lid is essential, as all Anthias are prone to jumping when startled.

Sexual Dimorphism (Male vs. Female):

Female: Females and juveniles are typically a beautiful yellow, yellowish-orange, or pinkish-yellow color. They are characterized by two faint horizontal purple or lavender stripes that run from the eye along the lower flanks toward the tail base. Their coloration is generally more subdued than the male's.
Male: The males are much bolder and more elaborate. They exhibit a deep pink-red to orange body color and are instantly recognizable by the large, distinct purple or magenta rectangular/square-shaped blotch centered on their flanks. They often feature red tips on the posterior dorsal fin margin and have a more elongated, lyre-shaped caudal (tail) fin.

Diet & Compatibility:

Diet: This fish is a dedicated Carnivore / Planktivore. Their natural diet consists of large quantities of suspended zooplankton, copepods, and other meaty micro-fauna.
Feeding: Due to their high metabolic rate and constant activity, they require small, frequent feedings, 3 to 4 times per day. Their diet must include a variety of high-quality, meaty foods such as frozen Mysis shrimp, enriched Brine shrimp, cyclops, and finely chopped seafood. They may also accept high-quality pellets over time.
Reef Compatibility: It is Reef Safe. The Squareback Anthias is an excellent addition to a reef aquarium, as it will not bother or nip at stony or soft corals. Its focus remains strictly on feeding from the water column.
Temperament: It is Semi-Aggressive within its species (conspecifics) but peaceful toward most other fish. Males are territorial and may be aggressive toward subordinate females or other Pseudanthias males. They thrive when kept in a proper harem structure to spread out the aggression. They should be housed with other moderately active, semi-aggressive fish.
Tank Requirements: Requires a minimum 100-125 gallon tank to provide sufficient open swimming space, along with plenty of stable live rockwork for hiding. They need strong water flow to mimic their natural habitat over deep reef slopes.

Quick Facts

Scientific Name: Pseudanthias pleurotaenia
Primary Common Name: Squareback Anthias
Other Common Names: Squarespot Anthias, Pink Square Anthias, Mirror Basslet, Square Shoulder Anthias
Origin: Indo-West Pacific (Widespread, including Fiji, New Caledonia, Indonesia)
Max Size: Up to 8 inches (20 cm)
Temperament: Semi-Aggressive (Territorial in groups, but peaceful otherwise)
Diet: Carnivore / Planktivore (Requires 3-4 daily feedings)
Minimum Tank Size: 100-125 Gallons
Reef Compatibility: Yes (Excellent)

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