Pajama Cardinalfish Breeding Guide
How to breed the Pajama Cardinalfish (Sphaeramia nematoptera), a paternal mouthbrooder, including spawning, egg incubation and rearing larvae on rotifers.
Overview
Sphaeramia nematoptera is a paternal mouthbrooder from the western Pacific that has been bred in home aquariums, though it remains uncommon. The species is socially monogamous, forming a long-term bond with a single partner, and copulation occurs year-round and throughout the day, more often at night. A bonded pair is the foundation of any breeding attempt.
Sexing
External sexual differences are subtle and the male is most reliably identified when he is carrying eggs in his mouth. Both males and females prefer to mate with fish of similar size to themselves, so grouping several individuals and allowing a pair to form naturally is the most reliable route to a compatible couple.
Conditioning
Because the larvae require live food immediately, rotifer cultures should be started at least three to four weeks before collecting an egg mass. Microalgae such as Nannochloropsis is needed to feed and enrich the rotifers, with the rotifers becoming enriched in the fatty acids and lipids crucial to the survival of newly hatched larvae.
Spawning Behavior & Trigger
Spawning tends to occur during evening hours. The female releases eggs, the male fertilizes them and scoops them into his mouth, and from that point he carries the egg mass and constantly adjusts its position. Once a pair begins spawning, they will typically spawn every two to three weeks.
Egg & Fry Care
The male broods the eggs in his mouth for several days; larvae start hatching between day seven and eight and swim out soon after, with the remaining egg mass gone by day nine. Breeders often collect the egg mass and hatching larvae from the male on day eight to rear them in a dedicated larval tank.
- First two weeks: feed S-strain saltwater rotifers; newly hatched larvae have a very small yolk sac and must find prey immediately.
- From day 5: enrich rotifers with a HUFA (highly unsaturated fatty acid) supplement.
- From day 12: introduce HUFA-enriched brine shrimp (Artemia).
- Week three onward: add a small pinch of 50-100 micron dry larval diet once a day.
- Metamorphosis completes between roughly 30 and 36 days post hatch.
Common Challenges
The pelagic larval phase makes this species harder to raise than the substrate-laying Banggai cardinalfish: larvae emerge as tiny slivers rather than fully developed juveniles. Supplying a continuous, correctly sized live food during the first two weeks is the principal bottleneck, which is why rotifer and microalgae cultures must be established before the eggs are collected.