Cardinalfish include some 330 species in 24 genera but are something of an unknown creature in diver terms as they tend to be small and shy, often hiding on the reef.
Cardinalfish are mainly marine fish although a few species are found in brackish and freshwater environments. They are small fish, usually under 10 centimetres long and can be recognized by their big eyes, large mouth and the division of the dorsal fin into two separate fins.
Cardinalfish tend to be homebodies, picking a nice looking patch or spot on the reef and then sticking to it. They are often described as nocturnal but this really means that during the day they shelter in small caves or dark crevices on the reef. A few species live in a more exposed position, but often on a darker dive site like a muck site with dark sand. Many cardinafish will take refuge with other animals – in the spines of an urchin or the tentacles of a coral.
Many males in this family are mouthbrooders meaning they hold and brood their eggs inside their mouth until they are ready to hatch.