Genus Sphaeremia: Pajamafishes.
Tropical marine, Atlantic, Indian and Pacific reefs; some estuarine and freshwater members (Papua New Guinea, see Allen).
Most to a few inches, some species to six-eight inches or more in the wild.
Cardinals display little middle-ground in their quality on-arrival; they are either hardy and sure to "make it", or thrashed and "doomed" to break down and die. For reference, they share many of the same selection criteria as damselfishes.
1) Behaviorally; look closely at the group on display. They should be clustered somewhat, with none having "private parties" off in the corners of the system. Are they aware of your presence? Good.
2) Reddening: Examine the bodies of each specimen carefully, especially the insertions of unpaired fins. Do you see evidence of infection on any individual? If so, pass them by.
Collecting Your Own
Gathering cardinals compared to other marines is a breeze. Apogonids are easily spooked out of hiding into a carefully placed hand net. Care must be taken in not snagging their dorsal fins' spines (6-8 in the first dorsal fin, one with 8-14 soft rays in second) and anal fin (two) spines.
Cardinals hide in the netherworld of ledges and corals by day; searching the bottom for food, by night.
Apogonids are about as tolerant as damselfishes; they are not demanding. Some temperate species prefer lower temperatures, but 72-78 degrees F. is fine for the group as a whole. Elevated temperatures may bring on a feeding strike and odd behavior. Higher, steady specific gravity is appreciated, closer to 1.025; maybe due to their close association with invertebrates?
Cardinals will tolerate a few tens of ppm of nitrate, but little or no ammonia, nitrite.
I'd like to mention that apogonids are an under-rated portion of the living reef's populations. Several of the hundreds of species are of large number in the wild, just not commonly encountered due to their largely nocturnal habits. Many form close associations with invertebrates, living within the spiny shelter of urchins, sea stars and more.
I'd shy on making it brisk. These fishes are found in areas where the water really whips at times.
For a really outstanding arrangement, provide a large dark shelter-space with one opening and a group of these fishes and others they are found with in the wild. The under ledge and cover sub-habitat is a rich biotope in the reef world.
Generally not. In the wild most live in aggregations as young and adults. In captivity they only fare well in groups.
Best put in established systems, keeping some low illumination on but subdued for a couple of days.
Most cardinalfishes as individuals get along with their own kind, other species of apogonids and other peaceful tankmates. Large predatory fishes will inhale them like so much aqua-popcorn if they're small enough.
The smaller species (some get to six inches) are strongly promoted for use in fish-only and reef-tank set-ups. They are supreme choices, being hardy and interesting; their only shortcomings being that they're shy and reclusive. Apogonids as a rule do not "sample" more than mouth-size invertebrates.
Reproduction, Sexual Differentiation/Growing Your Own: