Pajama Cardinalfish: Small, spotted reef fish known for male mouthbrooding.

This small marine species lives in the western Pacific and is prized by aquarium keepers. Males carry fertilised eggs in their mouths for weeks, a rare trait among reef dwellers that supports its popularity in home tanks.

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Males incubate eggs in their mouths for up to 31 days
Grows to a maximum length of 8.5 cm
Forms long-term monogamous bonds with partners
Found from the Ryukyu Islands to the Great Barrier Reef

What it is

This member of the Apogonidae family is a compact marine fish reaching about 8.5 centimetres. Its appearance is striking, with a greenish-yellow face and bright orange eyes. The body is silver, marked by a wide black vertical band around the middle. The rear section features scattered orange spots. Despite this vivid pattern, the animal remains peaceful in community tanks.

Where it lives

Populations exist across the western Pacific Ocean. The distribution covers areas from Java eastward to Fiji. Northern limits include the Ryukyu Islands, extending south to the Great Barrier Reef. These fish inhabit coastal reef systems within this broad geographic zone.

How it lives

Individuals form strict social hierarchies when kept in groups. Unlike many schooling species, they do not use aggression to establish dominance. They are socially monogamous, pairing with a single partner for multiple breeding cycles. If a mate dies, the survivor usually finds a new partner of similar size.

Breeding and life cycle

Mating happens year-round, often at night. The female releases eggs into the water, and the male fertilises them before scooping them into his mouth. He holds the clutch for eight to thirty-one days. Although pairs are monogamous, extra-pair fertilisation occurs. Males may carry eggs from other females, with unrelated eggs making up about 18 per cent of some broods.

A drawing made by EveryFish from what this page says. It is a diagram, not a picture of the real fish.

Fish and people

Aquarium enthusiasts value this species for its calm temperament and unique look. It fits well in saltwater community setups. The distinctive colouration and interesting reproductive behaviour make it a favourite among hobbyists who keep marine tanks.

Status and threats

The species faces low vulnerability in the wild. No major conservation threats are noted in the provided data. Its population appears stable across its wide Pacific range.

(EN) Pajama Cardinalfish - (FR) Apogon pyjama Sphaeramia nematoptera, South Komodo Island, Indonesia. Photo: Francois Libert, CC BY-SA 2.0, via Wikimedia Commons

Questions people ask about Pajama Cardinalfish

How big does the pajama cardinalfish get?

This species reaches a total length of approximately 8.5 centimetres. This compact size makes it suitable for smaller marine aquarium setups.

Do these fish care for their young?

Yes, the male performs mouthbrooding. After fertilisation, he holds the eggs in his mouth for eight to thirty-one days until they hatch.

Are pajama cardinalfish aggressive?

No, they have a peaceful nature. While they form social hierarchies in groups, they do not use aggression to dominate other members of their species.

Good reading and sources

Where this page comes from

The facts on this page come from the Wikipedia article "Sphaeramia nematoptera", written by its contributors and used under the CC BY-SA 4.0 licence, and from its Wikidata record (CC0). EveryFish rewrote the text in its own words, with AI assistance, and compares every page with the article to make sure no passage is copied. It may be reused under the same CC BY-SA 4.0 licence with a link back.

It may contain mistakes, and figures change over time. Nothing here is investment or buying advice. If something is wrong, tell us. Last refreshed 2026-11-15.

Photo credits on this page

The small pictures above come from Wikimedia Commons under free licences. Some are cropped to fit.