Preliminary Studies On Effects Of Dietary Nutrients On Skin Color Of Large Yellow Croaker(Pseudosciaena Crocea R.)

Based on the studies on skin color of cultured large yellow croaker, twofeeding trails were conducted to investigate the effects of two kinds of carotenoid ordietary lipid level on growth, anti-oxidative and skin pigmentation of large yellowcroaker. The results were summarized as follows:1. The skin color at night and in daytime, carotenoid contents in skin and muscle,melanin of dorsal and ventral skin of cultured large yellow croaker were studied.The lightness value of dorsal skin and redness values of dorsal and ventral skin indaytime were similar to those at night, while the lightness value of ventral skinwas higher in daytime. The carotenoid contents in dorsal and ventral skin were11.84mg/kg and30.67mg/kg, respectively. No pigment was detected in muscle.The melanin content in dorsal skin was83.82mg/kg and no melanin was found inthe ventral skin.2. A feeding trail was conducted in floating sea cages for nine weeks to investigatethe effects of astaxanthin and xanthophylls on growth, anti-oxidative capacitiesand skin color of large yellow croaker (initial weight33.33±1.67g). Fiveexperimental diets were made, which contain0,37.5mg/kg,75mg/kg astaxanthinor xanthophylls, respectively. The skin color at night was tested at the beginningand3th,6th,9thweek. The results showed that there were no affects of dietarycarotenoid on growth and anti-oxidative capacities. No significant difference inlightness of dorsal and ventral skin was found among all the treatments during thetrail. Astaxanthin treatments had higher redness than xanthophylls treatments bothin the dorsal skin and ventral skin. The yellowness of ventral and dorsal skinincreased during the feeding trail and the yellowness of xanthophylls treatmentswere higher than astaxanthin treatments both in dorsal and ventral skin. Thehighest values of carotenoid content in dorsal and ventral skin were appeared inthe xanthophylls treatments, but the lowest was found in the control treatment. The yellowness values of dorsal and ventral skin were correlated to the carotenoidcontent (r=0.935, P=0.020; r=0.926， P=0.024). The results suggest thatxanthophylls and astaxanthin can improve the skin color of large yellow croaker.3. An8-wk feeding trail was conducted to investigate the effects of dietary lipidlevel on skin color of large yellow croaker (initial weight10.02±0.02g). Sixexperimental diets were made, which contain3%,6%,9%,12%,15%,18%lipidand75mg/kg astaxanthin, respectively. The resultes showed that no significantdifference of dorsal and ventral skin lightness and redness were found amongtreatments; the yellowness of dorsal skin increase as the lipid level increased,though there was no significant difference. When the lipid level increased from3%to12%, the yellowness of ventral skin increased; but no further increase wasfound when the lipid level increased from12%to18%. No significant affect wasobserved in dorsal skin carotenoid content and melanin among treatments.Broken-line analysis based on the carotenoid content and yellowness of ventralskin indicated that the lowest requirement of dietary lipid for pigment of largeyellow croaker were13.187%and12.00%, respectively.