The acute stress response of red porgy, Pagrus pagrus, kept on a red or white background

The skin colour of red porgy, Pagrus pagrus, can be modified by exposure to different background colours. Red and white background colours brighten the dark skin colour that develops under common culture conditions in red porgy. To assess whether skin colour is also modified by aquaculture related handling stress, we subjected red porgy to 5 min of netting stress combined with air exposure. Fish kept on a white background have: (1) a lighter skin colour, which is not influenced by an acute stressor, (2) a less saturated red colour, which significantly decreases 24 h post-handling, and (3) a similar hue as fish kept on a red background. The first plasma parameters to rise after application of the stressor are cortisol, lactate and Na+; then, glucose levels rose. Other plasma ions (Ca2+, Cl−, K+) were not affected up to 2 h post-stressor, but had decreased at 8 and 24 h after handling. Plasma pH decreased over the first 2 h post-handling, indicative of plasma acidosis upon air exposure. The acidosis then coincided with increases in plasma lactate levels. As αMSH levels were not significantly affected by the stressor while cortisol levels showed a five to tenfold increase, we suggest that following acute stress in red porgy, plasma cortisol release is controlled by ACTH, perhaps in combination with a sympathic stimulation.