Why has my female Squareback Anthias turned pink and developed a square?

Squareback Anthias are protogynous hermaphrodites. In the absence of a dominant male, the most dominant female in the group will undergo a biological transformation, changing her sex to male and developing the vibrant pink-violet square marking on her side.

How often should I feed my Squareback Anthias?

Because they are highly active zooplankton feeders with fast metabolisms, they should be fed small portions of meaty foods like mysis or enriched brine shrimp 2 to 4 times a day.

Can I keep two male Squareback Anthias together in the same tank?

It is highly discouraged. Unless housed in an exceptionally massive public-sized aquarium, two males will fight relentlessly for dominance, often resulting in the death of the weaker fish.

Why is my new Squareback Anthias hiding in the rocks?

This is entirely normal behaviour during the acclimation period. In the wild, they use caves and overhangs to hide from predators. Ensure the water parameters are stable and offer enticing live or frozen foods to encourage them out over a few days.

Are Squareback Anthias safe to keep with corals?

Yes, they are completely reef-safe. They feed entirely on plankton in the water column and will ignore all corals, clams, and ornamental invertebrates.

MarineMarineIntermediate

Squareback Anthias

Pseudanthias pleurotaenia

A large and striking marine fish, highly prized for the male's distinct, luminescent violet-pink square patch that contrasts against its deep orange body.

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Ideal Conditions

Temperature: 22 – 26 °C
pH range: 8.1 – 8.4
Hardness: 15 – 25 dGH
Salinity: 1.02 – 1.026 SG
Adult size: 15 – 20 cm
Large Reef: 450 litres+
Lifespan: 5 – 10 years
Diet: Carnivore (Zooplanktivore)
Water flow: strong
Preferred setup: Steep rockwork with overhangs and ample open swimming space

About the Squareback Anthias

The Squareback Anthias, frequently traded as the Squarespot Anthias, is a captivating marine species belonging to the family Serranidae. They exhibit profound sexual dimorphism; males display an unmistakable vivid pinkish-violet rectangular patch across their midsection, creating a striking contrast against their reddish-orange bodies, while females are primarily yellow-orange and lack the square marking. Like all species in the genus, they are protogynous hermaphrodites, meaning dominant females will morph into males if the resident harem leader dies.

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Is it right for your tank?

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Where Squareback Anthias comes from

Native range

Indo-West Pacific, Western Pacific Ocean

Countries / regions

Indonesia, Philippines, Australia, Japan, Papua New Guinea, Samoa

Habitat

Deep coastal reefs and steep outer reef drop-offs in areas with strong tidal currents.

Commonly found at depths between 10 and 40 metres.

Similar species

Lyretail Anthias
Pseudanthias squamipinnis
Purple Queen Anthias
Pseudanthias tuka
Bimaculatus Anthias
Pseudanthias bimaculatus

We’re adding more full species guides as the catalogue grows.

Compatible tank mates

Reviewed guidance based on this species' recorded traits.

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Yellow Tang
Zebrasoma flavescens
Peaceful herbivores that do not compete for the anthias' planktonic food and share similar requirements for high flow.
Great
Fairy Wrasses
Cirrhilabrus spp.
Active, peaceful mid-water swimmers that complement the anthias well in a large reef aquarium.
Great
Lyretail Anthias
Pseudanthias squamipinnis
Mixing different species of Anthias can lead to severe territorial disputes between males in all but the largest aquaria.
Compatible with caution
Dwarf Lionfish
Dendrochirus spp.
Predatory species that may view juvenile or female anthias as a food source once they mature.
Not recommended
Seahorses
Hippocampus spp.
The boisterous, fast-feeding nature of the anthias will easily outcompete slow-moving seahorses for food.
Not recommended

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