Pajama cardinalfish
A peaceful, mouthbrooding cardinalfish with bold red spots and a dark waistband.
The pajama cardinalfish (Sphaeramia nematoptera) is a species of fish belonging to the family Apogonidae. It is also known as the spotted cardinalfish, coral cardinalfish, or polkadot cardinalfish. It is a popular aquarium fish distributed throughout much of the western Pacific Ocean, from Java to Fiji, and from the Ryukyu Islands south to the Great Barrier Reef. It is considered to be of low vulnerability.
Quick Facts
- Genus
- Sphaeramia
- Species
- nematoptera
Facts from the source article.
Lore & Background
The pajama cardinalfish features distinctive red eyes and a broad, dark, vertical 'waistband' with scattered red spots toward the tail. It has a greenish-yellow face, bright orange eyes, and a silver-based body with a bold black scalar margin and orange polka dots on the posterior. Despite its bold coloration, it has a peaceful nature that allows it to blend into most community saltwater aquaria. This species is distributed throughout much of the western Pacific Ocean, from Java to Fiji, and from the Ryukyu Islands south to the Great Barrier Reef. Like many other schooling fish, pajama cardinalfish form a strict hierarchy when kept in small groups within the aquarium, but they do not use aggression to exert dominance over other cardinalfish. Sphaeramia nematoptera is socially monogamous, meaning any individual male forms a long-term bond with a single female. The two fish stay close and mate for several breeding cycles, though extra-pair fertilizations have been observed. If one partner dies, the widowed fish is likely to form another bond. Both males and females prefer to mate with fish of similar size. Copulation occurs year-round and throughout the day, but is more common at night. The male incubates the eggs in his mouth until they hatch, a process lasting 8–31 days. Males may carry eggs from multiple partners, and only about 70% of all egg clutches result from monogamy with bonded social partners.
Reader's Guide
The pajama cardinalfish is a popular aquarium fish known for its peaceful nature and distinctive appearance. It grows to a total length of about 8.5 cm and features a bold dark vertical waistband with scattered red spots toward the tail. In the aquarium, it forms a strict hierarchy when kept in small groups, but unlike some social fish, it does not use aggression to exert dominance over other cardinalfish. This species is distributed throughout much of the western Pacific Ocean, from Java to Fiji, and from the Ryukyu Islands south to the Great Barrier Reef. It is considered to be of low vulnerability. In terms of reproduction, the male pajama cardinalfish is a mouthbrooder, holding fertilized eggs in its mouth for 8–31 days. The species is socially monogamous, with males and females forming long-term bonds, though extra-pair fertilizations occur. Males may carry eggs from multiple partners, and only about 70% of egg clutches result from monogamy with bonded social partners. The fish's peaceful nature and bold coloration make it a notable member of community saltwater aquaria.
Frequently Asked Questions
What is a Pajama cardinalfish?
The Pajama cardinalfish (Sphaeramia nematoptera) is a small, gentle member of the cardinalfish family Apogonidae, instantly recognizable by its bold red polka dots and a dark band circling its midsection. It has become a popular pick for reef aquariums across the hobby.
Why is it called the Pajama cardinalfish?
The common name comes from its eye-catching pattern of bright red spots paired with a dark 'waistband' stripe, which together look a lot like a pair of patterned pajamas. You'll also see it listed as the spotted, coral, or polkadot cardinalfish in the trade.
How big does a Pajama cardinalfish get?
Adults top out at roughly 8.5 cm (about 3.3 inches) in total length, making them a compact addition that suits smaller reef or nano setups without overwhelming the tank.
Where is the Pajama cardinalfish found in the wild?
Its natural range covers a broad stretch of the western Pacific, extending from Java eastward to Fiji and from the Ryukyu Islands south down to the Great Barrier Reef. The species is currently assessed as low vulnerability.
Is the Pajama cardinalfish aggressive toward tankmates?
No—this species is noted for its calm, non-aggressive temperament and generally coexists peacefully with other gentle reef fish. It's also a mouthbrooder, so the male carries the clutch in his mouth, a behavior many hobbyists love to watch.
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