Aquaticcommunity.com says:
Breeding Pajama Cardinalfish
Sexing the Pajama cardinalfish is hard but males usually have a longer secondary
dorsal than females and the females have somewhat rounder bodies than males.
The Pajama cardinalfish can be breed in aquariums and are relatively easy to breed. Once a Pajama cardinalfish pair have started breading they will breed regularly and often. The species is a mouth brooder and the male carries the eggs. The Pajama cardinalfish pair will be very aggressive during the spawning period. The male will protect the female until he takes the eggs in his mouth, after that the female will protect the male and chase away other fish. The male carries the eggs and fry in his mouth for about 3-4 weeks. He doesn't eat during this period.
Pajama cardinalfish fry are large and can eat newly hatched
brine as soon as they are released. The fry are aggressive and more aggressive fry will force weaker fry away from the food. It can be a good idea to separate aggressive and non aggressive fry into different aquariums if you want a
higher survial rate. The fry grow rather fast and is not as sensitive as many other marine fish fry.
From my dealings with breeding freshwater angels, I deduct that:
1) IF you have a male and a female and you notice that those 2 are agressive to everything that comes near, then you probably already have breeders.
2) IF you have breeders, then you must make sure that the male is well fed or he will end up swallowing the eggs he is carrying and you will never see fry.
3) IF you have anything in the tank that might get to the fry before you notice them, like perhaps a more agressive fish than the breeding cardinals, then the fry is getting eaten.
4) Some mouth brooders will invite the fry back into their mouths in the event of danger. Freshwater angels will accidentally swallow their young if you stand by the tank too long.
Tank you for your time and GL,
Kevin
