Effect of different carotenoid sources and their dietary levels on red porgy (Pagrus pagrus) growth and skin colour

Whereas wild specimens exhibit a red pink silver colour, under captivity red porgy (Pagrus pagrus) skin turns dark grey, being directly associated with lower acceptance by the consumers and lower market value. This study was conducted to evaluate the effect of diet supplementation with two carotenoid sources, at two different concentrations, on growth and skin coloration. Fish of 44 g mean initial weight were fed the following diets: control (with no added carotenoids), CTX 40 and CTX100 (diets with 40 and 100 mg of synthetic canthaxanthin/kg); SM20 and SM40 (diets with 20 and 40 mg of astaxanthin from shrimp shell meal/kg). Three samplings were carried out in this study, at the beginning and after 75 and 105 days of feeding. At each sampling, individual weight and colour measurements were performed. Colour was evaluated in three different body zones: front lateral (zone I), front dorsal (zone II) and caudal fin (zone III). Growth was not influenced by the inclusion of carotenoids in red porgy diet. Only astaxanthin from shrimp shell meal, particularly at 40 mg/kg diet, was able to give red porgy skin an overall reddish coloration, suggesting a better utilization of astaxanthin from this source. Shrimp shell meal diets enhanced reddish hue and chroma values, nevertheless hue values at days 75 and 105 did not show a marked difference and chroma attained after 75 days of feeding time tended to be reduced at day 105, suggesting skin colour saturation after a certain feeding time. Carotenoid supplementation did not influence lightness of red porgy skin in the present experiment. From the three evaluated zones, zone I of fish fed SM40 diet presented lower hue, chroma and lightness variation; therefore, it could be proposed as a control zone for future studies. The results of this study suggests that the inclusion of astaxanthin, from shrimp shell meal, in red porgy commercial diets significantly improves skin coloration and markedly enhances the commercial value of this cultured species.