Sphaeramia nematopterus
Pyjama cardinalfish
Currently accepted name: Sphaeramia nematoptera
The pyjama cardinalfish, known in Italian as pesce cardinale pigiama 5, is a small cardinalfish (Apogonidae) 1 up to about 8.5 cm long. 2 It has a yellowish head, a broad dark bar on the body and purple spots on the rear part. 3 It lives in groups among branching corals in sheltered bays and lagoons, and the male broods the eggs in his mouth. 2 3 9
At a glance
Data from the scientific sources listed at the bottom.
Depth in the wild
1–14 m
Size
up to 8.5 cm
maximum total length
Conservation
IUCN Red List: least concern (2021). Red List data taken from FishBase and GBIF. 2 4 It does not appear in the CITES lists checked on Species+. 6 An analysis of the aquarium trade lists it among only four heavily traded species (at least 15,000 specimens a year, according to 2011 US imports) that fall into the most vulnerable group. 12
Where it lives
From Java to Fiji, north to the Ryukyu Islands and south to the Great Barrier Reef, with a more recent record from Tonga. 2 In Australia it lives on the northern Great Barrier Reef and at the Cocos (Keeling) Islands, in the Indian Ocean. 3
How to recognise it
Tap a number on the photo: the key explains what to look for.
Life in the wild
Behaviour
It is strongly attached to its own site. 7 10 After its partner was removed, 78% of fish found another within two weeks at the same spot, and only 1 fish in 24 followed its partner when moved elsewhere. 7 In a displacement experiment over distances of up to 250 m, only 2 fish out of 37 returned home and 16 joined other groups, while 94% of the fish that were not moved stayed on their own corals. 10
Reproduction
The male broods the eggs in his mouth. 2 9 Pairs last a long time within larger groups, but they are not entirely faithful: of 105 clutches from 64 males, 30.1% had a mother other than the partner, 11.5% contained eggs from two females and 7.6% had been fertilised by two males. 8 Females are larger and more aggressive and have a longer filament on the dorsal fin: the sex roles turn out to be reversed compared with the more common pattern. 9
In the aquarium
From the experience of the BallingMania community.
The pyjama cardinalfish, as it is commonly called because of its distinctive livery, which indeed recalls a pair of pyjamas, is a very hardy and peaceful community fish. Its eyes are very large compared with the rest of its body, which shows its nocturnal habits; in fact, in the aquarium it is much more active at night than by day. It does not grow beyond 8.5 cm. Being a community fish, it should never be introduced alone into the tank but in a small group of 5-7 specimens; the strength of the group will make the individuals less shy. It is a fish that is rarely struck by disease and willingly accepts all types of food (from dry to frozen); in the wild it feeds on plankton and small invertebrates. It swims very slowly and often stays in the same area of the tank, typically among the branches of SPS corals, where it feels more sheltered and safe from possible predators. It has been bred successfully in captivity; like its cousin Pterapogon kauderni, it is a mouthbrooder: the female releases the eggs (every 2-3 weeks) and the male, after fertilising them, holds them inside his mouth and stops feeding for the whole incubation period.
Description and photo by: Giuseppe Rogliano
Did you know?
Sources
- Froese R., Pauly D. (eds.), via WoRMS (2026). Sphaeramia nematoptera (Bleeker, 1856). World Register of Marine Species.
- Froese R., Pauly D. (eds.) (2026). Sphaeramia nematoptera, Pajama cardinalfish. FishBase.
- Bray D.J. (2019). Sphaeramia nematoptera in Fishes of Australia. Museums Victoria.
- GBIF Secretariat (2026). Sphaeramia nematoptera, IUCN Red List category. GBIF.
- GBIF Secretariat, da Catalogue of Life (2026). Sphaeramia nematoptera, nomi comuni. GBIF.
- UNEP-WCMC, Segretariato CITES (2026). Search for Sphaeramia nematoptera in the CITES lists. Species+.
- Rueger T., Gardiner N.M., Jones G.P. (2018). Site fidelity facilitates pair formation in aggregations of coral reef cardinalfish. Oecologia.
- Rueger T., Harrison H.B., Gardiner N.M., Berumen M.L., Jones G.P. (2019). Extra-pair mating in a socially monogamous and paternal mouth-brooding cardinalfish. Molecular Ecology.
- Rueger T., MacDonald C., Harrison H.B., Gardiner N.M., Jones G.P., Mills S.C. et al. (2024). Strength of Sexual Selection and Sex Roles Vary between Social Groups in a Coral Reef Cardinalfish. The American Naturalist.
- Rueger T., Gardiner N.M., Jones G.P. (2016). Homing is not for everyone: displaced cardinalfish find a new place to live. Journal of Fish Biology.
- Pushchin I., Aleskerov N. (2024). Retinal ganglion cell topography and spatial resolving power in the pajama cardinalfish Sphaeramia nematoptera (Bleeker, 1856). Journal of Fish Biology.
- Baillargeon G.A., Wynn A.A., Baldisimo J.G.P., Tlusty M.F., Rhyne A.L. (2026). Evaluating species at risk in data-limited fisheries: A productivity-susceptibility analysis for marine aquarium fish. Ecological Applications.
Sources checked on 5 November 2026. Community texts and ratings are kept separate from the scientific data.