The effects of oxygen levels on oxygen consumption, survival and ventilatory frequency of sharpsnout sea bream (Diplodus puntazzo Gmelin, 1789) at different conditions of temperature and fish weight

The respiratory behaviour of the sharpsnout sea bream (Diplodus puntazzo) with fish weights between 15 and 509 g at temperatures of 15-29degreesC was studied, with special attention paid to critical and lethal oxygen saturation (S-crit and LC50, respectively) and ventilatory frequency (V-f). The species maintained a constant oxygen consumption rate regardless of the concentration of dissolved oxygen, until S-crit was reached. The mean of S-crit and LC50 was 34% (2.4 mg L-1) and 11% (0.8 mg L-1), respectively. The S-crit was independent of fish weight and temperature, whereas the LC50 values were positively correlated with both factors (P < 0.05). The higher resistance in small fish could be due to their greater V-f response to hypoxia than in larger animals. Furthermore, the increased metabolism resulting from the effect of temperature was offset by an increased V-f. The V-f remained constant down to a mean value of 67% oxygen saturation, regardless of fish weight and temperature. These findings suggest an optimum oxygen saturation of above 70% for D. puntazzo culture.