Review: Abdel Rahman El Gamal

Introduction: Gilthead seabream, Sparus aurata is called “dorade” in France, “Orata” in Italy, and “tsipoúra” in Greece. The species is generally appreciated by consumers. While the maximum recorded total length of the species was 70 cm and maximum weight about was 17 kg, the common standard length is about 35 cm. Based on fish ageing, the species could live for up to 11 years. This species is characterized as a sedentary fish, either solitary or in small aggregations.

 Distribution and habitats

Distribution: The gilthead seabream, Sparus aurata is a subtropical species that is the only species of the genus Sparus that belongs to the bream family, Sparidae. The species is naturally occurring in the Mediterranean Sea, and at the eastern coastal regions of the North Atlantic Ocean. Its euryhaline and eurythermal habits, enabled the species to occur in marine and brackish water environments such as coastal lagoons and estuarine areas.

Habitats: In the open sea, young gilthead is usually found whether singly or in small groups at depths of 0 – 30 meters, while adults are generally found at deeper depths of about 50 meters. They are found on rocky and seagrass beds or over sandy bottoms.

Description: Gilthead seabream is characterized by its oval, deep and compresses body. Its mouth is low with thick lips and four to six canine-like teeth anteriorly in each jaw. The color of the species is silvery with large a black spot on the gill cover. The gold bar marking between its eyes is related to “aurata”; the second part of the binomial name.

Feeding habits: Gilthead seabream is mainly carnivorous that feeds on shellfish, and also feeds on some plant materials.

Reproduction: Gilthead seabream is a protandrous hermaphrodite starting in the first two years as a functional male while turning into female afterwards at over 30 cm. Males enter puberty at 2 years of age (20-30 cm) and in females at 2-3 years (33-40 cm). Females are batch-spawners that can lay 20,000-80,000 eggs every day for an extended period of time.

Hatchery produced seed: The reduced availability of wild gilthead seabream seed as required by the farming operations necessitated the development of induced spawning techniques and the establishment of hatcheries. The artificial breeding was successfully achieved during 1980s in Italy, Spain and Greece.

The spawning of gilthead seabream can be done naturally based on the proper selection of ready-to-spawn broodstock or through the manipulation of key environmental parameters such as temperature and photo period. The spawning could be inducted using specific hormones. It that regard and because females are batch spawners, slow-releasing hormones are used to maintain the release of hormone over the spawning period.

Fertilized eggs of about 0.9 – 1.0 mm in diameter hatch into about 3.5 – 4.0 mm yolk sac larvae after about 48 h at 17-18ºC. As yolk is consumed in 2-4 days, larvae start preying on rotifers. As the larvae grow, artemia nauplii are offered to the advanced larvae. Afterwards, the appropriated feed of different quality and sizes is provided till reaching the targeted fingerling sizes.

Culture of gilthead seabream: As the wild catch of the gilthead seabream (about 10,000 tons) could not meet the market demand, the farming of the species has been justified especially in the Mediterranean region where most of the supply and demand occurs. After years of development, the total farmed bream amounted about 140,000 tons in 2010. The species is considered one of the most important fishes in saline and hypersaline aquaculture.

The extensive farming of the species has been practiced in coastal lagoons “valliculture” in Italy or in brackish ponds in Spain. In extensive system, polyculture of the species with other fish species has been normally practiced whereas production inputs are represented in fertilizers supplemented by commercial feed. Starting 1980s, the intensification of farming systems have been tested and commercially practiced in land-based tanks and sea cages.

The productivity of the species depends on the system in operation. While several hundreds of kilograms is produced of a hectar in extensive system, the productivity in tanks can range from 20-45 kg/m³ has been commonly obtained whereas water quality is highly controlled enabling higher stocking density and feed is usually of higher quality in such intensive system. The duration of the growing season depends on temperature and market size of harvested fish. For example, in off shore cages whereas the control on temperature is almost lacking, the average size of 350-400 g may be obtained in a period of 12-16 months while this period could be reduced in tanks whenever optimum temperature is obtained.  The current production of gilthead seabream places the species among the main farmed fin fishes in Europe.

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