Pajama cardinalfish

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.