Physiological Stress Responses in Strains of the Gilthead Sea Bream (Sparus aurata)

In this study we examined the physiological responses of different strains of gilthead sea bream (Sparus aurata) to chronic and acute stress factors. Blood glucose levels, hematocrit, and lactate concentrations were examined in yearlings of different strains of gilthead sea bream subjected to different stress situations. In the first experiment, fish of the Ardag and 'ebony' strains were kept 45 days in moderate (35-45 kg/m(3)) or high (70-90 kg/m(3)) density. There were no significant effects on the blood glucose level but, at both densities, hematocrit was significantly higher in the Ardag strain (33.2 +/- 3.0% at moderate and 44.5 +/- 1.6% at high) than in the ebony strain (22.0 +/- 3.0% and 19.9 +/- 2.7%, respectively). The interaction of 'strain' and 'crowding' was highly significant, suggesting that hematocrit may respond differently in each strain to crowding. In the second experiment, we examined the effects of acute stress (handling without anesthesia) among four strains representing Mendelian mutations that affect body coloration in gilthead sea bream: ebony, 'white', 'yellow', and the normally pigmented Ardag. Significant variations in the glucose and lactate concentrations suggest that genotypes of gilthead sea bream may have heritable differences in their physiological responses to stress factors.