**Squareback Anthias (Pseudanthias pleurotaenia)**

The Squareback Anthias, also known as the Purple Blotch Basslet or Squarespot Anthias, is one of the most visually distinctive and robust members of the Anthias subfamily. Known for its bold geometric markings and active nature, it serves as a stunning mid-water "utility" fish that adds both vertical movement and vibrant color to a reef or fish-only system.

Key Information

Common Names: Squareback Anthias, Squarespot Anthias, Mirror Anthias
Scientific Name: Pseudanthias pleurotaenia
Origin: Indo-West Pacific (Indonesia to Samoa, north to Japan)
Max Size: 20 cm (One of the largest Pseudanthias species)
Lifespan: 5–7 years
Temperament: Peaceful to semi-aggressive (more territorial than smaller anthias)
Diet: Carnivore/Planktivore – Requires high-protein meaty foods
Care Level: Moderate (Hardier than most anthias, but needs frequent feeding)

Water Parameters

Temperature: 22–26°C

pH: 8.1–8.4

Specific Gravity: 1.020–1.025

Minimum Tank Size: 380L+ (100 Gallons) for a single; 570L+ (150 Gallons) for a harem

Sexual Dimorphism & Appearance

This species is highly dimorphic, meaning males and females look like entirely different fish:

Males: Feature a deep pink-to-orange body with a large, shimmering lilac-to-purple rectangular spot on their flanks. Their fin tips often have mauve or red accents.
Females: Predominantly bright yellow or orange-yellow, often with a subtle lavender-pink belly and a thin blue/purple line extending from the eye to the pectoral fin.
Hermaphroditism: Like your interest in the Watanabe’s Angelfish, these are protogynous hermaphrodites. In a group of females, the largest and most dominant individual will physically transform into a male.

Behavior & Tank Compatibility

The Squareback Anthias is a bold, open-water swimmer that prefers the mid-to-upper levels of the aquarium.

Social Structure: They thrive best in a harem (one male to 4–6 females). Keeping multiple males will lead to intense aggression.
Reef Compatibility: They are completely reef-safe. They do not bother corals, clams, or ornamental shrimp.
Tank Mates: Compatible with peaceful to moderately aggressive fish. They pair well with the reef-safe angelfish you’ve explored, such as the Lamarck’s or Watanabe’s. Avoid keeping them with overly aggressive "bullies" that might prevent them from feeding.

Ideal Tank Setup

Strong Flow: They naturally inhabit outer reef slopes and drop-offs; strong water movement is essential for their oxygen needs.
Rockwork: Provide significant rockwork with large caves and overhangs for shelter during the night or if they feel threatened.
Lighting: This species naturally lives in deeper waters (up to 180m). They prefer dimmer, indirect lighting; their vibrant colors may actually fade under intense, high-PAR reef lights.
Tight-Fitting Lid: Like all anthias, they are notorious jumpers, especially when startled.

Why Choose the Squareback Anthias?

The Squareback is the "heavyweight" of the anthias world. It is significantly more resilient to environmental fluctuations than smaller, more delicate species like the Dispar or Ventralis Anthias. For a large display, they provide a constant "shimmering" effect in the water column and possess a high level of intelligence and social interaction that makes them a favorite for seasoned marine hobbyists.

Marine Fish - Anthias

Anthias Lyretail Male (Lyretail Squamipinnis)

Anthias Squareback (Pseudanthias Pleurotaenia)

Anthias Lyretail Female (Anthias Squamipinnis)

Anthias Princess (Pseudanthias Smithvanizi)

Anthias Tuka

Anthias Ventralis Female

Anthias Sunburst

Anthias Ventralis Male

Anthias Blotchy

Anthias Aurulentus

Anthias Twotone (Nemanthias Dispar)

Anthias Hutchii