Cardinalfish, from the family Apogonidae, are unique among reef dwellers for being primarily nocturnal and having a fascinating mouth-brooding reproductive strategy. Usually staying between 2 and 4 inches, these fish are easily identified by their large, expressive eyes and two distinct dorsal fins. Because they are naturally active at night, they tend to hover nearly motionless in the water column or near rocky overhangs during the day, making them a very peaceful and calming addition to a saltwater setup. Unlike many other reef fish that are highly territorial, many cardinalfish species are schooling fish that feel most secure and look their best when kept in groups of five or more.
In a home aquarium, cardinalfish are considered excellent beginner fish because they are incredibly hardy and reef-safe. They are carnivores that feed on small plankton and meaty bits in the water column, but they generally leave corals and larger invertebrates alone. One of their most interesting traits is that the males are mouth-brooders. After females lay eggs, the male will carry them in his mouth for several weeks, protecting them until they hatch. Cardinalfish prefer tanks with low to moderate water flow and plenty of rocky “nooks” where they can hang out during the day before becoming more active when the lights dim.
