Cardinalfishes are a family, Apogonidae, of ray-finned fishes found in the Atlantic, Indian, and Pacific Oceans; they are chiefly marine, but some species are found in brackish water and a few (notably Glossamia) are found in fresh water. A handful of species are kept in the aquarium and are popular as small, peaceful, and colourful fish.
They are generally small fish, with most species being less than 10 cm (3.9 in), and are often brightly coloured. They are distinguished by their large mouths, and the division of the dorsal fin into two separate fins. Most species live in tropical or subtropical waters, where they inhabit coral reefs and lagoons.
They are nocturnal, spending the day in dark crevices within the reef. At least some species brood their eggs inside the mouths of the males.