Closed Cycle Aquaculture

Closed Cycle Aquaculture

Sea Bass, Sea Bream and Meagre

Commercial-scale closed cycle aquaculture operations in Malta started with the production of gilthead seabream Sparus aurata and European seabass Dicentrarchus labrax in 1990. The production processes employed for both species are virtually identical, although the performance indicators for these species differ somewhat. Both species’ production is based on the supply of hatchery-reared juveniles, with no reliance on wild stocks – closed cycle.

Juvenile seabass and seabream are purchased from overseas hatcheries at a size of between 1g and 3g, and are delivered by truck to Malta, with a typical delivery time of 2-4 days. Specialized live fish transportation trucks are used for shipment, and transport-related mortalities are generally very low, amounting to a few percent. Upon arrival in Malta, the juveniles are discharged into small transport cages and then towed out to the nursery cage site.

Because of the small size of the juveniles the production of seabass and seabream requires that the initial growth stages be carried out at sheltered inshore locations. At a size of 30-50g the seabass or seabream can then be transferred to semi-exposed offshore sites for on-growing to the usual market size of 300-500g.

Seabass and seabream are fed on proprietary pelleted and extruded feeds, formulated specifically for these species. Typical feed formulations include a protein content of 40-50% and an oil content of 15-20%. A lot of research work is being carried out by feed companies to replace fish meal and fish oil components with vegetable-based products such as soya meal and soyabean oil to reduce costs and to reduce reliance on marine-based products.

Some producers routinely grade their fish stocks, primarily to assist in marketing a uniform-sized product. Whereas seabream is relatively resistant to handling operations, seabass is very sensitive and are not normally handled beyond an average weight of 50-100g.

The bulk of seabream and seabass produced in Malta is exported by truck fresh, on ice, to Italy. Seabream are sold as whole portion-sized fish, of 300-400g average weight, packed in 6kg polystyrene boxes. Because of higher mortality rates and a vulnerability to the viral disease VNN, the cost of production of seabass is higher than that of seabream. Consequently, seabass production has dropped significantly in recent years.

Seabream producers have shown some interest in the production of meagre, Argyrosomus regius, over recent years, following the availability of juveniles of this species from commercial hatcheries. Production methods and systems are identical to those used for seabass and seabream, and so bass and bream producers can grow this species without the need for dedicated production systems. Growth rates are impressive, with fish reaching an average weight of 1.2kg within 12 months at a food conversion ratio of only 1.25, and survival rates are good. The main constraint to the expansion in the production of this species is poor market demand, however, and so production volumes can be expected to remain low unless some market development is carried out to increase demand.​