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Even in this summer of 2025, like every summer, we witness the birth and growth of the Black Damselfish, Chromis chromis, the only one of its kind Pomacentridi – Pomacentridae – in the Mediterranean Sea. In these sequences we see it in its shining electric blue livery, when the little fish are still small, a few weeks after the hatching of the eggs laid in winter, spring by the females and guarded by the male until the birth and first growth of the fry.
Blue damselfish Chromis chromis Castagnole blu intotheblue.it
The blue color is then lost during the development of the little fish until only a small line remains with the one that will then predominate black livery. This phenomenon is repeated every summer and we can find these blue fish from a few meters up to 15 meters deep, provided that there are inlets in the rock and shaded areas where they can take refuge in case of danger.
This species bases its existence on large numbers, the young are born in many specimens of many different couples synchronized almost at the same time, and then they aggregate in schools of many specimens. The defensive strategy lies precisely in the fact that predators will find themselves confused in front of many small blue splinters that move in unison in various directions.
As you can also see in the video these little fish make sudden dashes in unison in various directions to escape the attacks of certain predators such as the Saddled Bream (Oblada melanura).
Blue damselfish Chromis chromis Castagnole blu intotheblue.it
Chromis chromis, commonly known as Damselfish, is a saltwater fish belonging to the family Pomacentridae, of which he is the sole representative in the Mediterranean.
Distribution end habitat
The damselfish is widespread in the Mediterranean (where it is very common) and in the eastern Atlantic between Portugal and the Gulf of Guinea (more rarely to Angola).
Populates the shallow rocky bottoms where he lives in benches scattered in midwater. They are also found on the oceanic Posidonia meadows. Small specimens still with the blue livery are fotofobi and often encounter in caves, crevices and other shady environments.
Blue damselfish Chromis chromis Castagnole blu intotheblue.it – Occhiata – Oblada melanura
Description
It has an oval body, flattened, with small mouth and big eyes. The dorsal fin is unique, with front spiny rays and longer rear soft rays, the anal fin has only two spines followed by many soft. The caudal fin is notched in the middle and has two pointed lobes. The upper and lower rays of this fin are darker than the rest giving the impression of a queue engraved more than it is in reality. The ventral fins and pectoral fins are quite developed. The flakes are large.
Blue damselfish Chromis chromis Castagnole blu intotheblue.it
Young fishes have a bright blue color, while the adult specimens lose it gradually with the growth to become dark brown or blackish with longitudinal rows of lighter spots on the sides. The coloration can vary: the males spawning are very dark while the adults pale night. It reaches a maximum length of 16 cm but it is usually much smaller.
Reproduction and behavior
Breeding takes place in the summer, the male performs a wedding dance to persuade the female to go on the part of the seabed that will serve as a nest. There, the deposition occurs for about 10 minutes after which the female is immediately driven away. The eggs are not floating but they stick to the substrate due to the adhesive filaments of which are equipped and are actively defended and oxygenated by the male.
Supply
It feeds on smaller fish and invertebrates such as worms, crustaceans, and tunicates.
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