Abstract
Arthrospira platensis is rich in protein, vitamins, minerals, essential amino acids, pigments carotenoids, essential fatty acids and antioxidant compounds. Carotenoids, including lutein, β-carotene, astaxanthin and so forth, which dissolve in fat and result in yellow, red, orange, and green pigmentation of the eggs, skin, and flesh of many fish species. Antioxidant compounds, such as phycocyanin, and tocopherols have significant effects on scavenging free radicals. Lutein is considered as an effective functional compound benefiting human health and widely used as a natural food colorant due to its antioxidant potential and the intense yellow color. However, high density in intensive aquaculture has let to outbreaks of bacterial infections that caused high mortality of yellow catfish, which impeded the further rapid development of the yellow catfish culture industry. Nutritional and environmental factors can cause abnormal body color, which also has a negative effect on the quality and value of fish. To evaluate the effects of Arthrospira platensis and lutein on the growth, pigmentation, antioxidant capacity and disease resistance in hybrid yellow catfish (Pelteobagrus fulvidraco♀×Pelteobaggrus vachelli♂), four isonitrogenous (400 g crude protein/kg diet) and isolipidic (85 g crude lipid/kg diet) diets containing 2% A. platensis (SP), 0.2% lutein (Lut), 2% A. platensis with 0.1% lysophospholipids (SPL) and without pigments (Control) were designed. A total of 720 fish initial body weight of (4.79±0.01) g were stocked into 12 tanks at a density of 60 fish per tank. Fish were fed a diet without pigments for 20 days, then fed four experimental diets for 35 days. A bacterial challenge test using Aeromonas hydrophila was subsequently conducted. The results indicated that there were no significant difference in final body weight (FBW), specific growth rate (SGR) and feeding rate (FR) among all groups (P>0.05). The feed efficiency (FE) of the 2% A. platensis and 2% A. platensis with 0.1% lysophospholipids groups were significantly higher than those of the 0.2% lutein and control groups (P<0.05), and supplementing 0.1% lysophospholipids significantly increased feed efficiency (P<0.05). The protein retention efficiency (PRE) of the control group was the lowest (P<0.05), and 2% A. platensis with 0.1% lysophospholipids had the highest PRE (P<0.05). The chemical composition results showed that there were no difference on moisture, crude protein and crude lipid of the whole body of each group (P>0.05), while the ash content in 0.2% lutein and 2% A. platensis groups were lower than the control group (P<0.05). There was no difference on the skin lightness between different groups, while the skin yellowness of the 2% A. platensis and 2% A. platensis with 0.1% lysophospholipids groups were significantly higher than those in the 0.2% lutein and control groups (P<0.05). The skin redness of the 2% A. platensis with 0.1% lysophospholipids group was significantly higher than the control group (P<0.05), and the redness of dorsal skin in the 2% A. platensis group had similar results. The skin chroma of the 2% A. platensis and 2% A. platensis with 0.1% lysophospholipids groups were significantly higher than those in the 0.2% lutein and control groups (P < 0.05). The lutein contents in abdominal skin of the 2% A. platensis and 2% A. platensis with 0.1% lysophospholipids groups were 18.65 and 18.10 µg/g, respectively, which significantly increased compared with the control group (13.16 µg/g) and the initial level (13.32 µg/g) (P<0.05). There was no significant difference in lutein content in dorsal skin among all groups (P>0.05). The experimental fish fed 2% A. platensis and 2% A. platensis with 0.1% lysophospholipids had better body color. Dietary A. platensis and lutein significantly increased the activities of plasma SOD (P<0.05). The activities of plasma GPX and the contents of plasma GSH in the 2% A. platensis with 0.1% lysophospholipids group were higher than those in the 0.2% lutein and control groups (P<0.05). The MDA contents decreased significantly in the 2% A. platensis and 2% A. platensis with 0.1% lysophospholipids groups (P<0.05). 96h post challenge with A. hydrophila, the cumulative survival rates of yellow catfish of 2% A. platensis, 2% A. platensis with 0.1% lysophospholipids, 0.2% lutein and control groups were 20.83%, 16.67%, 5.55% and 0, respectively. The cumulative survival rates of yellow catfish of 2% A. platensis, 2% A. platensis with 0.1% lysophospholipids were significantly higher compared to those of 0.2% lutein and control groups (P<0.05). In conclusion, supplemental A. platensis can increase pigmentation and enhance total antioxidant capacity and disease resistance of hybrid yellow catfish. Lutein can also effectively enhance pigmentation, and lysophospholipids can significantly improve feed utilization. However, dietary A. platensis is more effective than lutein in improving the body color and enhancing antioxidant capacity and disease resistance of hybrid yellow catfish.
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