Cardinalfish are widely distributed throughout the world's tropical seas, mostly along reefs, but also in tidal pools and mangrove swamps. They are classified in the Apogonidae family and are small predatory fishes that sport various shades of reds, yellows or brown. Many species have distinct stripes and spots, and none grows to more than five inches in length. Their most distinguishing characteristic is their pair of unusually large eyes, which scientists believe is what allows them to see better at night when they feed on small invertebrates and fishes. These little fish usually hide out for most of the day under overhangs and other nooks.
Some cardinalfish have evolved the habit of playing dead when attacked or frightened, so don't be overeager to flush away your pet unless you are absolutely sure it's not merely reacting to a scare of some kind.
Although in nature you will find schooling cardinalfish, it's not a good idea to add more than two to any aquarium, and, ideally, those two should be male and female. As juveniles, cardinalfish will peaceably school in your aquarium, but as they grow older dominant males begin to establish their pecking orders. Once a dominant male has chosen his mate, he will often harass the others to death - literally. Success stories vary when it comes to keeping odd numbers of cardinalfish. To avoid problems, it may be easier to stick with pairs and, in some cases, only a single pair.
Overall, these species are quite hardy to keep in a home aquarium, making them popular among hobbyists. They require a diet of meat and vegetable foods and the usual water-quality ranges for sustaining a healthy reef tank. Cardinalfish are usually shy eaters. They accept just about any food, but they need a little more time than other fish to acclimate to a new environment and may not eat during that period. Feeding them live brine shrimp during the acclimation process has often been the key to getting them used to their new surroundings. Many species of cardinalfish are commonly available for the home aquarium.