The effect of density on sea bass (Dicentrarchus labrax) performance in a tank-based recirculating system

Sea bass (Dicentrarchus labrax) (135±4g) were reared under tank-based recirculating aquaculture system for a 63-day period at four densities: 10, 40, 70, 100kgm−3. Fish performance, stress indicators (plasma cortisol, proteonemia plus other blood parameters—Na+, K+, glucose, pH, total CO2−) and water quality were monitored. At the end of the 63-day period, resistance to infection was also studied by a nodavirus challenge. A 25-day test was performed on fish from two extreme densities (10 and 100kgm3) and one intermediate density (40kgm3). With regards to the different density treatments, there was no significant difference between the daily feed intake (DFI) and the specific growth rate (SGR) up to a density of 70kgm−3. No significant difference was found between treatments concerning the feed conversion ratio (FCR) and the mortality rate. No density effect was observed on the fish stress level (plasma cortisol) or on sensitivity to the nodavirus challenge. Under these experimental rearing conditions, the density above 70kgm−3 has an impact on growth performance (DFI and SGR) indicators and also some blood parameters (CO2) at the highest density tested (100kgm−3). This study suggests that a density up to 70kgm−3 has no influence on sea bass performance and welfare. At 100kgm−3, average specific growth rate was decreased by 14% without welfare deterioration according to the welfare indicators monitored.