The seabass, Dicentrarchus labrax, Linnaeus 1758, is a Perciform fish, belonging to the Moronidae family and to the genus Dicentrarchus.

(European Sea Bass, Sea Bass, Seebarsch)

Position on Systematics (Taxonomy):

Superphylum:   Metazoa

Phylum :          Animalia

Subphylum:      Vertebrata

Superclassis:    Gnathostomata

Classis:            Pisces

Subclassis:       Osteichthyes

Superordo:       Actinopterygii

Ordo:               Teleostei

Subordo:         

Family:             Moranidae

Genus:             Dicentrarchus

Species:           Dicentrarchus labrax (Linneaus,1758)

Fig. 1 - Adult specimen of seabass

Fig. 2 - Adult specimen of seabass

Family Description

Family Moronidae

Perciform fish of elongated body. Operculum with two flat spines; terminal mouth slightly protractile; end of the maxillary visible, not gliding under the sub-orbital bone; small teeth on the jaws and vomer, without canine teeth. Two dorsal fins separated, the first one with 8-10 spines, the second with one spine and 11-14 soft rays; anal fin with three spines and 10-12 soft rays; base of the pelvic fins without scales; caudal fin moderately forked. Large caudal peduncle. Lateral line complete, not continuing on the caudal fin. Small scales, around 55-80 on the lateral line in the Mediterranean species. Colour generally silvery; one species with small black spots; lower fins sometimes yellowish when fish are alive.

Medium to large size fish (till one meter total length) of temperated and cold regions. The two species of the Mediterranean inhabit coastal and brakish waters and are occasionally found in rivers.

Two species occur in the Mediterranean Sea: D. labrax (L.) and D. punctatus (Bloch), the latter with only a marginal interest in artisanal fishery along the southern Mediterranean coasts. They can be identified on the following characters:

Biology

Morphology

The seabass, Dicentrarchus labrax has a silvery elongated body, with two clearly differentiated dorsal fins and a rather high tail. The opercular bone has two flat spines and a range of spines are visible in the lower part of the preopercular bone, pointing in the direction of the mouth. The vomer presents teeth with a crescent shape. This species has cycloid scales in the interorbital region. The lateral line is visible as a dark line with 62-80 cycloid scales.

The first dorsal fin has 8-10 spiny rays, and the second dorsal fin 12-13 rays of which the first is spiny. The anal fin has 3 spiny rays and 10-12 soft rays.

The colour is dark grey on the back, passing to grey-silver on the sides, while it is white-silver on the abdomen. Specimens from the sea show a much clearer colour than fish from lagoons and estuarine environments. On the opercular bone there is a dark spot. The juveniles show a livery with little dark spots, mainly on the front or only on the head, which disappear with age. The maximum size is over 1 m with a weight of over 12 kg.

The seabass is a eurythermal and euryhaline species and can survive at temperatures between 2 and 32°C, with a limited territoriality related to their search for food and to reproduction. Outside the spawning period, the seabass can be found anywhere food is available. Maturation and spawning need more specific environmental conditions (temperature, photoperiod, salinity) which determine variation in spawning period.

Feeding

Seabass is a predator consuming small fish and a large variety of invertebrates. In spite of variations associated with differences in latitude, bass hunts at any time of the day. The feeding behaviour is related to size. Juveniles feed mainly on small Crustaceans (Amphipoda, Mysidacea, Isopoda) and small fish (about 1/4 of the diet), like Atherina and Gobius. In fish larger than 20 cm, shrimps and crabs begin to be common preys.

Geographic distribution

D. labrax is common in the Mediterranean Sea, the Black Sea and along the Eastern Atlantic coasts from Great Britain to Senegal. With a tolerance to salinity and temperature fluctuations greater than the gilthead seabream, this species is found in marine to slightly brackish environments such as coastal lagoons and estuarine areas. In particular during the first stages of its life cycle displays the same behaviour of gilthead seabream. Much less sensitive to low temperatures, some fish may overwinter in coastal lagoons instead of returning to the open sea.

Reproduction

In seabass sexes are separate: the female shows a deeper body with a longer pointed head and greater pre-dorsal and pre-anal lengths. Sure sex confirmation is however possible only during the spawning season by checking the presence of sperm by squeezing gently the males and by observing the protrusion of the anus and genital papilla in the females.

Fig. 3 - European seabass geographic

Sexual maturity takes place earlier in males and earlier in Southern populations. There is only one breeding distribution season per year, which takes place in winter in the Mediterranean population (December to March), and up to June in the Atlantic populations. Unlike gilthead seabream, female gonads complete their maturation at the same time and eggs are released all together in a short time, usually at night. For hatchery purposes, spent females have to be replaced by new breeders as soon as new batches of eggs are required.

After being released, the eggs acquire their characteristic spherical shape, with a size that varies according to latitude:

Fisheries

Seabass is fished both by artisanal and sport fishermen. The quantities caught in the Mediterranean are relatively small which linked to high appreciation for the species in the Mediterranean markets makes it a high value species. The gear used to catch seabass include beach and purse seines, trawl nets, trammel nets and longlines, as well as rod and line. It is regularly present in the Mediterranean markets but it is scarce in the eastern Mediterranean basin and it is rare in the Black Sea.

References: Fao,2005