|Studie van de biologie en de kweek van zeebaars Dicentrarchus labrax (L.) in intensieve aquacultuurcondities|
Verdonck, W. (1989). Studie van de biologie en de kweek van zeebaars Dicentrarchus labrax (L.) in intensieve aquacultuurcondities. PhD Thesis. Katholieke Universiteit Leuven (KUL): Leuven. 160 pp.
In Europe. the interest in sea bass (Dicentrarchus labrax) as a culture fish is fast increasing. This results in a rapid expansion of sea bass culture and of that of other marine fish species. such as seabream (Sparus aurata) and turbot (Scophtalmus maximus). In 1983 a research project was started, with the aim of culturing sea bass in the thermal effluents of the nuclear power station at Doel. In this way the possibility of producing valuable proteins is created while at the same time thermal effluents, normally dumped as waste heat, can be put to good use. The biology of the sea bass. In the Atlantic Ocean, the distribution area for sea bass ranges from Marocco to Norway. It is also found in the entire Mediterranean sea. The species has only one reproductive period, independent of the latitude. Spawning usually occurs in the littoral zone, in water with a salinity of above 30 promille. The juvenile stages, however, are mostly found in brackish, shallow waters, which function as "nursery grounds" due to their rich food supplies. This food mainly consists of invertebrates and, although some adult piscivore sea bass can be found, crustaceans remain the most important food items. Sea bass are very euryhaline and eurytherm, which has been experimentally determined and which can also be concluded from their local and geographical distribution. Sea bass as culture fish. Although sea bass culture only became popular in the eighties, a strong interest in the technique has developed owing to the high quality of the meat yielded and its subsequent high market value. The extensive culture is mainly situated in Italy where, in the "'allicultura", 700 tons are harvested yearly. However, while during cold winter months mortality is high, the yield per surface unit in extensive culture is limited. For this reason nowadays more interest, research and money are invested in the intensive culture system where densities up to 60 kg/m² are obtained. Besides the less applied pond culture, net cages and tanks are mainly used in intensive sea bass culture, depending on the suitability of the site. Both culture methods have advantages and disadvantages. Culture in tanks allows a better control of the fish population and the output per m² is higher than that in cages. However, financial investments for cage culture are much lower when compared to tank culture. In Europe the most important sea bass producing countries are France, Italy, Spain, Greece and Yougoslavia. Together they produce about 6000 tons of sea bass and sea bream per year. The high prices which can rise to 600 Bfr/kg, and which can show a yearly increase of about 20 %, are expected to stabilize in the near future. A decrease, however, is not to be expected because supply of fry is very limited and prevents a fast increase of production. A direct consequence of the shortage of juveniles is their high price, which rises to above 35 Bfr/piece. The pilot plant at Doel. The first culture experiments with sea bass in our country date from 1982 and were performed at the Zoological Institute of the K.U.Leuven. Due to a number of problems inherent to the recirculation system, which was used in this experiment, we started in 1983 by building a pilot installation for the culture of sea bass and eel on the K.C.D. grounds. When this installation was completed in 1985, the total effective water surface was 90 m², divided over 4 round and 6 square tanks. The water supply is derived from the River Scheldt, from the cooling tower and from the condenser circulation, in order to optimize the temperature and oxygen concentration of the culture water in the tanks throughout the year. In the tanks, the water is renewed once an hour; it leaves the tank through a central exit, which is constructed in such a way that, during the cleaning process, all the silt deposit is removed. Each tank is provided with extra aeration and an automatic feeding system (EWOS Multic feeder). The water temper