Effect of temperature and dissolved oxygen concentration on the metabolic rate of the turbot and the relationship between metabolic scope and feeding demand

Turbot Scophthalmus maximus maximum oxygen uptake following feeding and exhaustive exercise increased from 107 mg O2 kg −1 h −1 at 6° C to c . 218 mg O2 kg −1 h −1 at 18° C, then increased slightly from 18 to 22° C to 224 mg O2 kg −1 h −1 . Standard oxygen uptake increased exponentially as a function of temperature from 11 mg O2 kg −1 h −1 at 6° C to 66 mg O2 kg −1 h −1 at 22° C. Gradual reduction in oxygen concentration to 87–90% air saturation at 6, 10. 18° C and <80% at 14 and 22° C limited the maximum metabolic rate but, supersaturation (>100% saturation) had little effect. Metabolic scope attained a maximum of 176 mg O 2 kg −1 h −1 at 18° C. Interpolation of the results showed that this value changed little between 16 and 20° C. It is suggested that this temperature range is optimal for turbot of c . 500 g. A comparison with a previous study on feeding demand in intensive farming conditions showed a linear relationship between appetite and metabolic scope. It is concluded that the ability of a fish to supply energy (including the energy requirement of digestive metabolism) above a standard level is a limiting factor in the manifestation of its feeding demand.