Effect of temperature on the metabolism, behaviour and oxygen requirements of Sparus aurata

We investigated the effect of temperature on the limiting oxygen saturation (LOS) of gilthead sea bream Sparus aurata. This threshold was defined as the % O₂ saturation where fish no longer upheld their routine metabolic rate (RMR, the metabolic rate of fed and active fish) during a progressive decline in oxygen saturation. S. aurata (398 ± 10 g, mean ± SE) were kept in 3 replicate tanks and subjected to 3 changes in temperature: 16 to 20°C, 20 to 16°C and 16 to 12°C. At each temperature, fish were left to acclimatize for 8 to 10 d, before daily feed intake (DFI), the routine oxygen consumption rate (routine MO₂, mg kg⁻¹ min⁻¹) and the LOS were measured. In addition, at 20°C the swimming speed was measured in fish subjected to a decline in O₂ from full air saturation to levels below the LOS (minimum of 8−10% O₂). For the temperature range tested (12−20°C), DFI, MO₂ and LOS increased exponentially with temperature (7.5-, 3.6- and 2.2-fold, respectively) with mean (± SE) LOS being 17 ± 1, 21 ± 0 and 35 ± 5% O₂ at 12, 16 and 20°C, respectively. A gradual decline in swimming activity was observed as O₂ declined below the LOS, indicating increasing metabolic stress and/or a 'sit-out' coping strategy which may prolong survival time in severe hypoxia. The results show the importance of temperature as an influential variable over the environmental O₂ requirements of S. aurata.