Effects of dietary xanthophylls/astaxanthin ratios on the growth and skin pigmentation of large yellow croaker Larimichthys crocea (Richardson, 1846)

An 8-week feeding trial was conducted to evaluate the effects of dietary xanthophylls/ astaxanthin ratio on the growth and skin color of large yellow croaker, Larimichthys crocea. Five pigment-supplemented diets were formulated to contain 75/0, 50/25, 37.5/37.5, 25/50 and 0/75mgkg(-1) of xanthophylls/astaxanthin. The xanthophylls contain 89.31% lutein and 6.12% zeaxanthin. A diet without pigment supplementation was used as the control. The large yellow croaker juveniles (13.80 +/- 0.03g) were randomly distributed in 18 sea cages (1.0x1.0x1.5m) at a density of 45 fish per cage. Water temperature ranged from 21 to 31 degrees C during the feeding trial. To obtain results, the survival rate, specific growth rate, feed conversion ratio, skin redness, skin yellowness, skin lightness, skin carotenoid content and skin melanin content were measured. The results showed that the survival rate, specific growth rate and feed conversion ratio were not significantly affected by dietary treatments (P>0.05). The ventral skin lightness was also not affected by dietary treatments (P>0.05); however, the dorsal skin lightness of fish fed with the control diet was significantly lower than those fed with pigment-supplemented diets (P<0.05). The lowest values of yellowness and carotenoid content both in the ventral skin and dorsal skin were found in the control group. Yellowness and carotenoid content increased with an increasing proportion of dietary xanthophylls in both the ventral and dorsal skin. Higher redness values were found in the compound pigment groups, either in the dorsal skin or ventral skin. Fish fed with the control diet showed a higher melanin content in the dorsal skin than those fed with pigment-supplemented diets, although differences were not significant (P>0.05). Lightness and yellowness were linearly related to skin carotenoid content. Meanwhile, skin yellowness and carotenoid content were linearly related to the proportion of xanthophylls in dietary pigments.