The impact of different rearing condition on gilthead seabream welfare: Dissolved oxygen levels and stocking densities

Aquaculture's success highly depends on a controlled rapid growth of organisms with minimal costs associated. Growth and welfare of reared organisms are affected by physical, chemical, and biological parameters. Following factors can be highlighted as crucial: density, pH, salinity, temperature, dissolved oxygen (DO), and nutrients (nitrogen, phosphorus, etc.). Relationship between fish density and oxygen's optimum levels is essential for designing the performance of each species. Furthermore, it is also necessary to study fish stress factors and physiological responses. Two rearing experiments with gilthead seabream (Sparus aurata) were performed, in order to test different densities (5, 10 and 20 kg/m(3)) for 9 weeks (271 +/- 1.9 g) and to test different levels of oxygen (40%-60%, 60%-80%, and 80%-100%) for 6 weeks (316.3 +/- 1.73 g). In both experiments, physiology and growth parameters were analysed, as well as water quality. This study showed that no relation was observed between density and fish physiology, but there structural (gill lesions) and physiological changes (haematocrit) were observed for seabream reared at low levels of DO.