Effects of husbandry conditions on the skin colour and stress response of red porgy, Pagrus pagrus

Red porgy, Pagrus pagrus, is a potential candidate for aquaculture. However, darkening of the body occurs after capture of wild fish and during fanning of cultured animals. In fish, skin pigmentation is hormonally controlled and the main hormone involved in skin darkening, alpha-melanocyte-stimulating hormone (alphaMSH), is not only involved in pigmentation but also in the regulation of the response to stressors. In this study, several environmental conditions were evaluated for their potency to influence the skin colour and to evoke a stress response. Background colour was the main factor in controlling skin pigmentation. A light background colour restored the lightness value of the skin up to levels found in wild red porgy (L*=similar to70). The background effect was enhanced by applying blue illumination. Light intensity had no clear effect on the body colour, but a high density of fish had a negative effect on the lightness. Plasma parameters (cortisol, alphaMSH, glucose, lactate and osmolality) were not influenced by background colour. A stocking density of 25 kg/m(3) did not evoke a stress response in contrast to earlier studies on red porgy, nor influenced the body colour. We propose that this difference can be attributed to the number of fish per volume of water, which was lower than in other studies. This indicates that the number of fish per volume of water rather than the density in kilograms of fish per volume of water is the relevant factor. Furthermore, we suggest that the culture of adult red porgy can be optimised by maintenance of fish on a light background, thereby restoring the body colour to a more natural hue, without affecting the stress response. (C) 2004 Elsevier B.V. All rights reserved.