Diplodus sargus, first described by Linnaeus in 1758, is a polymorphic species that includes seven subspecies distributed worldwide. The subspecies are: D. sargus ascencionis, D. sargus cadenati, D. sargus capensis, D. sargus helenae, D. sargus kotschyi, D. sargus lineatus, and D. sargus sargus.
D. sargus sargus, known as the common two-banded seabream, is distinguished from others by the presence of nine dark vertical bands on the upper part of its back. These bands tend to disappear in adults over 20 cm in length. This demersal and coastal fish typically lives at depths ranging from 40 to 180 meters but can go as deep as 420 meters. Juveniles are found in very shallow waters, forming small groups or schools near Posidonia oceanica meadows and rugged seabeds, often composed of rocks, coarse sand, gravel, or pebbles.
This seabream has a wide geographic distribution. D. sargus can be found throughout the Mediterranean, except in the Black Sea. D. sargus cadenati is common along the West African coast, from the Strait of Gibraltar to Cape Verde, around the Madeira and Canary Islands, and extends north to the Bay of Biscay. D. sargus capensis is found from Angola to Mozambique and in southern Madagascar, while D. sargus lineatus is endemic to Cape Verde.
The common two-banded seabream plays an important ecological role, and various studies have been conducted on the species in both the Atlantic and the Mediterranean. The feeding regime and trophic ecology of D. sargus have been extensively studied on the northern coasts of the Mediterranean, but less so on the southern coasts, especially in North Africa.
In the summer, the white seabream can often be found in small groups very close to the substrate, in Posidonia meadows or on shallow rocky bottoms. In winter, it moves to deeper waters with a stable temperature. This fish particularly favors harbor breakwaters, artificial reefs, and shallow coral reefs, where it can find its preferred prey, mussels. When disturbed, it takes refuge in cavities under rocks. Juveniles are euryhaline (but do not tolerate high salinity like seabass or gilt-head bream) and move to brackish waters and lagoons in the spring, returning to the sea in the autumn. The young arrive in lagoon or estuary areas as larvae in June in the Mediterranean. Here, they spend the summer growing. As soon as they sense the first temperature drops, they leave the lagoons to seek a more stable environment (in the sea) to continue their life.
Although the white seabream is mainly found in rocky areas, it is not uncommon to find it in sandy areas, both small and large individuals. In this case, the small ones tend to join small groups of salemas (Lithognathus mormyrus). The white seabream is a common fish with a length of 15-30 cm, which can reach up to 45 cm. Like all Sparids, it has a single dorsal fin. The body is oval, tall, and laterally compressed. The lips are thin, and the mouth is slightly protrusible. It has 8 incisors on each jaw and several rows of molars.
The dominant coloration is silver-gray, with a grayish-beige back and dark gray coloration on the interorbital area and the snout. The opercula are usually bordered in black, and a dark saddle-shaped spot is visible on the caudal peduncle. This does not reach the lower edge of the peduncle. A dark spot is also found on the rear base of the pectoral fins. The pelvic fins are dark with a white front edge. The rear part of the caudal fin is dark.
Young individuals have 8-9 dark vertical stripes on the upper part of the back, which can disappear in adults (starting at 20 cm in length in the Mediterranean subspecies Diplodus sargus sargus).
The color of the white seabream in the Mediterranean varies depending on the fish’s location: in very clear biotopes (sandy areas), individuals will be very light, and the stripes and spots tend to disappear even in young fish. In contrast, in areas with dark rocks, the white seabreams will be darker, and the stripes will be more visible. The stripes also tend to appear, and overall darkening occurs when the fish is stressed by a predator, conspecific, or other factors. During the nighttime resting phase, the white seabream assumes a darker coloration, highlighting its stripes.
The white seabream can be confused with Diplodus annularis, which has yellow pelvic fins, and especially with Diplodus puntazzo, which has a more pointed snout and more numerous vertical stripes. The spot on the caudal peduncle of D. annularis and D. puntazzo forms a complete ring, unlike that of Diplodus sargus sargus, which does not reach the lower edge.
Young white seabream are omnivorous, and adults are carnivorous. They feed on worms, crustaceans, mollusks, and echinoderms. Their robust molars allow them to break shells, carapaces, and tests.
To be more precise, during their first year of life, these fish consume small crustaceans (isopods), small worms, and any other prey they can swallow. They are very voracious until the age of one year. When they reach a length of about 15 cm (1-2 years), they shift toward a diet based on bivalve mollusks (especially mussels), sea urchins, and occasionally crustaceans (shrimp, crabs).
The sexes are separate. Sexual maturity is reached at the age of 2 years (around 17 cm). The species is protandrous hermaphroditic, first male, then female; the change of sex occurs at about 5 years. Although most individuals change sex, some do not (> 5%), and the white seabream is called protandrous.
Reproduction occurs from March to June in the western Mediterranean and from January to March in the eastern Mediterranean. After reproduction, the larvae spend a month in plankton in open water before colonizing the coast in early June in rocky areas no deeper than 1 m. From this point on, we are talking about young individuals, which spend the summer feeding and trying to escape strong predation (scorpionfish, sea bass, cuttlefish, squids, gobies, etc.). Starting from June, it is not uncommon to observe large quantities of young white seabream in harbors.
This species is very common and not very shy, especially in marine reserves. It is quite difficult to keep in an aquarium with other fish due to its territorial nature.