Long having been one of the most ubiquitous cardinalfish in the aquarium trade, the pajama cardinalfish (Sphaeramia nematoptera) looks somewhat like a Franken-fish! The head is yellow with a bright red eye and a blue jaw, the midsection is black with obvious checkered board pattern, while the rear half of the fish is white with brown spots. The unusual color pattern and its reputation for being almost bullet-proof have made it a favorite for decades.
Difficulty: The pajama cardinalfish is a durable fish that will do well in the aquarium of the inexperienced fishkeeper but is interesting and attractive enough to be of interest to the more seasoned hobbyist. The pajama cardinalfish will eat about anything, voraciously accepting prepared foods for carnivores, frozen mysid shrimp, Cyclops, fish eggs and finely chopped seafood. It is prudent to feed the pajama cardinalfish at least once a day (two or three times a day if you are conditioning them for breeding). The pajama cardinalfish rarely has any problem with disease or parasites.
Physical description: The pajama cardinalfish has a very unique color pattern (described above), large pelvic fins (which are black in juveniles and yellow in adults) and a large second dorsal with a long filament. The orbicular cardinalfish (Sphaeramia orbicularis) is the pajama cardinal’s uglier cousin. It is silver overall, with small black flecks on the head, a black line down the middle of the body, and black spots on the rear body and caudal peduncle.
Range: The pajama cardinalfish is found in the western Pacific, from Japan south to the Great Barrier Reef and east to the Fijian Islands. This pajama cardinalfish tends to occupy very shallow water (less than 30 feet), hanging out around large stands of staghorn corals (Acropora spp.). The pajama cardinalfish does most of its feeding at dusk and dawn, at which time it leaves the cover of ramose corals to capture zooplankton. It has also been known to consume fish eggs, polychaete worms and small fish.
Compatibility: The pajama cardinalfish is a passive fish that does well in a peaceful fish community (although it may be a threat to smaller anemone shrimp and nano-gobies). Otherwise, it is benign. Adult Sphaeramia nematoptera may squabble if kept together, if the aquarium is too small and you have two males in too small an aquarium (e.g., less than 75 gallons).
Like other cardinalfish, it is likely to be pestered by dottybacks, large hawkfish, damsels (e.g., Pomacentrus, Neoglyphidodon and Stegastes), pygmy angelfish and hostile wrasses (e.g., Cheilinus, Pseudocheilinus and Thalassoma).
Aquarium conditions: Unlike many of the apogonids, the pajama cardinalfish does not refuge in reef cracks and crevices during the day. It tends to hang out in groups over branching corals. If threatened, the pajama cardinalfish will sink in among the coral branches. In the aquarium, you should attempt to create similar refuge types. This may be live stony corals or faux staghorn corals. Acceptable water parameters for the pajama cardinalfish would be: pH of 8.1 to 8.4, specific gravity of 1.019 to 1.025 and a water temperature of 77 to 84 degrees Fahrenheit.
Care considerations: The only way you don’t have success keeping Sphaeramia nematoptera is if it is housed with pugnacious species that torment it so much that it refuses to eat.
Breeding: If you have a group of pajama cardinalfish in your aquarium, you will occasionally see an individual that has swollen “chops” like a hamster with cheeks full of food. This appearance indicates that you have a male incubating a mass of eggs. This egg mass can consist of from 6,000 to almost 12,000 eggs. The pajama cardinalfish can spawn every three or four weeks. If they spawn that often, the male pajama cardinalfish will often lose weight and is more likely to eat the precious egg bundle (this is known as filial cannibalism) – you can’t blame him, its either that or possibly starve to death!