Pyjama Cardinalfish

The Pyjama Cardinalfish (Sphaeramia nematoptera) is a small cardinalfish (family Apogonidae) named for its distinctive spotted, pajama-like pattern. It is found throughout the Indo-Pacific, from Indonesia and the Philippines to Papua New Guinea and neighboring island regions. It is not considered threatened and is a common sight on sheltered reef habitats, often noted for its unusual boxy body shape compared to more streamlined reef fish. Its bold, unmistakable pattern makes it a frequently photographed species and a subject of interest for reef fish behavioral studies related to nocturnal cardinalfish biology.

Identify this species by its two-toned pattern:

• Compact, rounded, slightly humpbacked body shape
• Front half pale reddish-brown to yellow with a bold dark vertical bar through the large eye
• Rear half silvery-white covered in numerous orange-yellow spots
• Large eyes adapted for low-light activity
• Small adult size of 6-8 cm The striking two-part color division and heavy dark eye bar make this species essentially unmistakable among Indo-Pacific reef fish.

Pyjama Cardinalfish inhabit sheltered lagoon and inshore reef environments, typically in shallow water from about 1 to 15 m depth. They favor calm, current-protected areas such as coral branches, sea urchin spine clusters, and reef crevices that provide daytime shelter. Their range spans the western and central Indo-Pacific, including Indonesia, the Philippines, Papua New Guinea, and northern Australia. They prefer warm, stable tropical reef water and are rarely found in exposed, high-surge locations, instead favoring quiet bays and protected reef flats.

Pyjama Cardinalfish are nocturnal, sheltering in small stationary groups among coral branches, urchin spines, or crevices during the day and dispersing to feed on zooplankton after dark. They are generally non-aggressive and form loose aggregations rather than strict schools, often hovering motionless close to their shelter site. Like other cardinalfish, males are mouthbrooders, incubating fertilized eggs in their mouths until the young are ready to disperse into the plankton. This paternal care strategy improves egg survival compared to species that broadcast spawn, and the species plays a role in reef food webs as both a zooplankton predator and prey for larger reef fish.