Pisciculture intensive du tilapia Sarotherodon niloticus dans les effluents thermiques d'une centrale nucléaire en Belgique

This paper presents the results of three years of experiments in cultivating the tilapia Sarotherodon niloticus in the cooling waters of the nuclear power station of Tihange on the Belgian river Meuse. The research station infrastructure is currently composed of three earthen ponds measuring 150 m2 (volume : 200 m3) and 16 fibreglass tanks of 4 m2 (2 m3). These ponds and tanks are fed by a pumping system (70 m3/h) at the outlet point of the power station condenser. A regulation system ensures that the feed-water is kept at a safe thermal level (17-32 °C). The Meuse has a high biological productivity potential at Tihange ; there is no chemical pollution of any significance, although moderate organic pollution is existing. The thermal conditions in the river make it possible to count on nine months (March to December) during which the average usable water temperature for tilapias culture exceeds 20°C. S. niloticus appears to be a species of considerable potential : it has no difficulty in supporting temperatures of around 35-40°C and as low as 8-10°C for a few hours and oxygenation rates in the order of magnitude of 0.5-1,0 mg/l. The production cycle takes 8-9 months to complete : natural reproduction in pools, growth of the fry from 5 to 25 g in the pools or tanks, separation of the sexes, growth of the males from 25 to 350 g in tanks and then in pools, with artificial feeding at all stages. The growth rate and subsequent length of the production cycle depends on many factors : temperature, size of the fish, stocking density and oxygen content. Under conditions of intensive tank culture, it was possible to maintain a maximum biomass (with 150 g fish) of 120 kg/m3 of tank with a water renewal rate of about 3,5 times per hour (loading : 2,1 kg/liter per minute). A figure is provided showing the relation to fish weight of oxygen consumption and optimal loading at a temperature of 30-32 °C. The highest yield recorded are 21,1 g/m3 per hour and 25,7 kg/m3 of tank per month with an average yield of 12g/m3 per hour. A volume of 85 m3 of heated water is required to produce 1 kg of S. niloticus from 20 g of male fry. These tilapias are suitable for marketing (trial offer to restaurants) when they weight 300-350 g. Analysis show that their heavy metals and radio-nucleide content is below the level permitted by law.