Apogon imberbis, the Cardinalfish, also known as the Mediterranean Cardinalfish or King of the Mullets, is a colourful fish widely distributed in the Mediterranean Sea and along the warm temperate and tropical eastern Atlantic Ocean coasts. However, although it is found throughout the Mediterranean Sea, Apogon imberbis does not extend north into the Black Sea.
The Cardinalfish has a compressed, ovate body with a large head and very large eyes, much larger than the snout. It has a large, oblique mouth with a protruding lower jaw, which contains rows of small villiform teeth on the mandible, palatine and vomer. The preopercular margin is only slightly serrated and the preopercular ridge is smooth.
The pectoral fin of the Mediterranean Cardinalfish is long, reaching to at least the origin of the anal fin, while the caudal fin shows slight emargination. The scales are large and ctenoid in form, and the lateral line numbers 22 to 30 scales. The body and fins are coloured red or pink, duskier on the back and upper surface of head. Along the base of the caudal fin, there are two or three dark spots which are occasionally joined.
The maximum recorded size of Apogon imberbis is 15 cm standard in length, although 10 to 12 cm is more usual. The two dorsal fins have a total of 7 spines and 9 to 10 soft rays, while the anal fin has 2 spines and 8 to 9 soft rays.
The Cardinalfish is frequently found on rocky reefs as well as artificial structured reefs from 2 to 20 metres in depth, most especially where there are rocky cliffs and caves. In winter they appear to move to deeper waters. It feeds on small fish, invertebrates and plankton. In the Atlantic, it associates with coral and rocky reefs.
Apogon imberbis is nocturnal and spends the day in cavities or caves, either individually or in small shoals. They can often be abundant on artificial reefs, especially in the Mediterranean.
The Cardinalfish breeds from June to September. It is a mouthbrooding fish (a.k.a. oral incubation); that is, after internal fertilisation of the eggs, the male broods the balls of eggs in his mouth.
Photo taken by Brian Azzopardi