| Large yellow croaker is one of the most important mariculture speicses in China. However, farmed large yellow croaker lost its natural color to some extent under high intensity culture conditions. This study was conducted to investigate the skin color control by the methods of nutriology. The aim of this study is to provide basic data for promoting the skin color of farmed large yellow croaker.1. Effects of dietary lutein/canthaxanthin ratio on the growth and pigmentation of large yellow croaker Larimichthys croceus.This study was conducted to investigate the effects of dietary lutein/canthaxanthin ratio on the growth and skin coloration of large yellow croaker. Five pigments supplemented diets were formulated to contain 75/0,50/25,37.5/37.5.25/50 and 0/75 mg kg-1 of lutein/canthaxanthin. The diet without pigment supplementation was used as the control. Fish of the similar size (13.83 ± 0.04 g) were fed with these experimental diets for 8 weeks in sea cages. Results showed that there were no significant differences in survival rate, specific growth rate and feed conversion ratio among the all treatments (P>0.05). The ventral skin lightness (L*) was not affected by dietary treatments (P>0.05). However, the dorsal skin lightness (57.94) in the treatment of control was significantly lower than those in the treatments with supplemented dietary carotenoids (P<0.05). The lowest values of yellowness (b*), redness (a*) and carotenoid content both in ventral and dorsal skin were found in the control. Yellowness and carotenoid content both in ventral skin and dorsal skin decreased with the decreasing of the proportion of dietary lutein. Meanwhile, the redness increased with the increasing of the proportion of dietary canthaxanthin. Fish fed with the control diet had higher melanin content (83.82mg/kg) in the dorsal skin, though no significant differences were found. Coloration parameters (L*ã€a* and b*) were linearly related to the carotenoid content in skin. Meanwhile, yellowness, redness and carotenoid content were linearly related to the proportion of dietary lutein. In conclusion, under present conditions, both lutein and canthaxanthin are needed in the diet for large yellow croaker. Compared to the lutein, higher dietary canthaxanthin contents are better for the skin redness.2. Effects of dietary lutein/astaxanthin ratio on the growth and skin pigmentation of large yellow croaker Larmichthys crocea.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. Five pigment supplemented diets were formulated to contain 75/0,50/25,37.5/37.5, 25/50 and 0/75 mg/kg of lutein/astaxanthin. The diet without pigment supplementation was used as the control. Fish (13.80 ± 0.03 g, n=810) were randomly distributed into 18 sea cages (1.0 × 1.0 × 1.5 m) at a density of 45 fish per cage. The water temperature fluctuated from 21 to 31℃ during the experiment. Experimental parameters (survival rate, specific growth rate, feed conversion ratio, skin redness, yellowness and lightness, skin carotenoid and melanin content) were measured at the end of the feeding trial. 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 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 pigments 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 lutein in both ventral and dorsal skin (P<0.05). Higher redness values were found in the compound pigments groups either in dorsal skin or ventral skin. Fish fed with the control diet showed higher melanin content in dorsal skin than those fed with pigments supplemented diets, though no significant differences were found (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 lutein in dietary pigments.3. Effects of dietary fish oil replaced with rapeseed oil on the growth, fatty acid composition and skin color of large yellow croaker Larmichthys crocea.An 8-week feeding trial was conducted to investigate the effects of dietary fish oil replaced with rapeseed oil on growth, muscle fatty acid compositions and skin color of large yellow croaker (initial weight 13.56±0.05g). Five isoproteic and isolipidic experimental diets were formulated with 0%,25%,50%,75% and 100% replacement of fish oil by rapeseed oil. Results showed that these replacements did not significantly influence on the survival rate (SR) and specific growth rate (SGR) (P>0.05). However, the feed conversion ratio (FCR) was increased with the increasing of replacement levels. Furthermore, FCR in the group of 100% rapeseed oil was significantly higher than that with 100% dietary fish oil (P<0.05). No significant difference was observed on the whole body compositions (P>0.05). The concentrations of C18:0, C18:1, C18:2n-6, C18:3n-3 and the saturate fatty acid (SFA), not C20:4n-6 and C22:5n-3 in muscle, were elevated with the increasing of dietary rapeseed oil levels. There were no significant differences in yellowness (b*) of dorsal and ventral skin among the five treatments (P>0.05). Lightness (L*) of the dorsal skin in the treatment with 100% dietary rapeseed oil was significantly higher than that with 100% dietary fish oil (P<0.05). However, L of the ventral skin was not significantly different among the all treatments (P>0.05). Higher redness (a*) of ventral skin and lower a of dorsal skin were found in fish fed with 0% rapeseed oil. This study suggested that there were no significant effects of replacement of dietary fish oil by rapeseed oil on growth and body composition. However, the fatty acid composition of muscle and the skin color were significantly influenced.4. Shrimp shell meal in diets for large yellow croaker Larimichthys croceus: effects on growth, body composition, skin coloration and anti-oxidative capacity.A 9-week feeding trial was conducted to evaluate the effects of dietary shrimp shell meal (SSM) on the growth performance, body composition, skin coloration and anti-oxidative capacity of large yellow croaker Larimichthys croceus. A control diet (SM0) without SSM, a diet with 12% of SSM (SM12) and a diet with 2 4% of SSM(SM24) were each fed to three groups of 70.24±0.20 g large yellow croaker. Results showed that the specific growth rate (SGR), survival rate (SR) and protein efficiency ratio (PER) in the SM24 group were significantly lower than those in the SM12 and SMO groups (P<0.05). The whole-body lipid content in SM24 group was significantly lower than that in the other two groups (P<0.05). The skin coloration and carotenoid content were significantly improved with the supplementation of SSM in the diet (P<0.05). Compared to those in the SMO group, dorsal skin melanin content and tyrosinase activity were significantly higher in SM12 group and SM24 group (P<0.05). The amount of thiobarbituric acid reactive substances (TBARS), the superoxide dismutase activity (SOD) and the concentration of reduced glutathione (GSH) in the liver were not significantly affected by dietary SSM (P>0.05). However, the total anti-oxidative capacity (T-AOC) in the SM12 group was significantly higher than that in SMO. In conclusion, dietary SSM can improve the skin coloration with no negative effects on the anti-oxidative capacity of large yellow croaker. However, high dietary SSM (24%) decreased the growth performance and whole-body lipid content.5. Effects of dietary vitamin E and astaxanthin on growth, skin color, and anti-oxidative capacity of large yellow croaker Larmichthys crocea.A 10-week feeding trial was conducted to evaluate dietary vitamin E and astaxanthin on growth performance, skin color, and anti-oxidative capacity of large yellow croaker. Six practical diets were formulated in a 2 × 3 factorial design to supplement with 2 levels of astaxanthin (25 and 50 mg/kg) and 3 levels of vitamin E (0,120,800 mg/kg). Each diet was fed to triplicate groups of fish (initial weight:3.00 ± 0.01 g). The results showed that the highest final body weight (FBW) and specific growth rate (SGR) were shown in fish fed diets with 120 mg/kg vitamin E supplementation. No significant differences were found in survival rate (SR), feed conversion ratio (FCR) and protein efficiency ratio (PER) among all the treatments (P>0.05). Skin lightness (L*) was not significantly affected by dietary treatments (P>0.05). Ventral skin redness (a*) of fish fed diet with 25 mg/kg astaxanthin and 0 mg/kg vitamin E supplementation was significantly lower than that of fish fed with other diets. Yellowness (b*) and carotenoid contents both in the dorsal and ventral skin were significantly increased with the increasing of dietary astaxanthin or vitamin E (P<0.05), but no significant interactions were found (P>0.05). The vitamin E content of liver reflected the vitamin E content of the diets but also affected by dietary astaxanthin being significantly increased by astaxanthin in fish fed diets supplemented with 800 mg/kg vitamin E. Liver superoxide dismutase (SOD) activity and thiobarbituric acid reactive substances (TBARS) levels were decreased with the increasing of dietary astaxanthin and vitamin E respectively. Liver reduced glutathione (GSH) content was increased with the increasing of dietaiy vitamin E. Liver total anti-oxidative capacity (T-AOC) was decreased with the increasing of dietary vitamin E or astaxanthin. In conclusion, adequate dietary vitamin E can improve the growth of large yellow croaker and the supplementation of astaxanthin and vitamin E benefited the skin coloration and anti-oxidative capacity of large yellow croaker.Appendix chapter. Effects of light intensity on growth performance, skin coloration, antioxidantive and stress responses of large yellow croaker Larmichthys crocea.This study was conducted to investigate light intensity on the growth performance, skin coloration and stress response of large yellow croaker. Three light intensity treatments were 412 lx,156 lx and 17 lx, which represented high light intensity (HL), middle light intensity (ML) and low light intensity (LL), respectively. Feed was formulated with 44% crude protein and 13% crude lipid, which contained 50mg/kg astaxanthin as pigment source. Fish (initial weight:56.25±0.00g) reared in flow water system for 30 days. Results shown that specific growth rate (SGR), condition factor (CF) and feed intake (FI) in LL group were significantly higher than those in HL groups (P<0.05). Lightness (L*) of ventral and dorsal skin was not significantly affected by light intensity (P>0.05). However, the redness (a*) of ventral skin and yellowness (b*) of ventral and dorsal skin were increased with the decreasing of light intensity. Cortisol and ACTH of serum in the HL group were significantly higher than those in the LL group, while glucose and LDH in the LL group were significantly higher than those in the HL and ML groups (P<0.05). The highest T-AOC, GSH and CAT values in liver were appeared in the LL group, but the highest TBARS and SOD values in liver were shown in the HL group. In clusion, under the present conditions, low light intensity was good for the growth and skin color of large yellow croaker, which also reduced the stress and improved the antioxidant response. |
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