The Cardinalfish is a small, reddish fish that lives primarily on rocky bottoms and in caves. It belongs to the Apogonidae family, and its scientific name translates to "beardless" because it lacks the whiskers found on red mullet, with which it shares a similar red colour. The body is short and high, with an intense orange-to-red colouration. Its most characteristic features include the massive eyes, which betray its nocturnal habits, and the large oblique mouth. It often bears two or three dark spots at the base of its tail.

The species is a nocturnal predator. It feeds mainly on small invertebrates such as shrimp and copepods, as well as on the eggs and larvae of other fish it finds in the plankton at night.

The Cardinalfish has an extremely interesting reproductive method known as mouthbrooding. Breeding takes place in the summer and usually from June to September. After fertilisation, the male takes the eggs, which are joined in a ball, into his mouth. He holds and protects them there until they hatch, which takes approximately 5 to 7 days. During this period, the male does not feed at all, and he aerates the eggs by opening and closing his mouth.