| Astragalus polysaccharide(APS)is a water-soluble heteropolysaccharide possesses immune-enhancing function that extracted from Chinese herbal medicine Astragalus.Furong crucian carp is the offspring produced by the female parent Cyprinu carpio L.mirror and the male parent Cyprinus carpio var.singguoensis.In order to figure out the functional effects of APS on the Furong crucian carp,in this study,different proportions(0.00%,0.05%,0.10%and 0.15%)of APS were added to the diet,and a 67-day feeding experiment were carried out,with a 7 days of pre-feeding trail.After the feeding experiment,indexes relating to the growth,meat quality,plasma biochemical and immune of the Furong crucian carp were detected;the survival status of the fish in each experimental group infected with Aeromonas hydrophila were evaluated.The purpose of this study is to clarify the functional effects of APS on the growth,meat quality and immunity of Furong crucian carp,and to provide a basis for the application of APS in aquaculture diets.The main results are as follows:Effects of APS addition on growth and meat quality.Compared with the non-addition group,the weight gain rate and specific growth rate of Furong crucian carp were significantly elevated,and the feed coefficient was significantly reduced in the 0.05%addition group(P<0.05);The weight gain rate,specific growth rate and relative fatness of Furong crucian carp were improved and the dietary coefficient was reduced in 0.10% and0.15% addition groups,compared with 0.05% addition group whereas no significant change was observed.For the meat quality,the addition of 0.05% APS could improve the muscle elasticity,adhesiveness and chewiness of Furong crucian carp.In addition,0.10% and 0.15%APS addition could improve the viscosity of Furong crucian carp,and reduce the cohesion.Moreover,the muscle hardness,content of crude protein and crude fatty were improved to some extent in all APS addition groups.Effects of APS addition on plasma biochemical parameters.Compared with the non-addition group,the 0.05% and 0.10% APS addition could significantly improve the total antioxidant capacity(T-AOC)and the catalase(CAT)activity(P<0.05).In addition,the content of malondialdehyde(MDA)in each APS addition group was significantly decreased,whereas the tumor necrosis factor α(TNF-α)level was significantly increased(P<0.05).Effects of APS addition on the comprehensive status of immune organs.Compared with the non-addition group,the length of intestinal villi were significantly increased,and the number of lymphocytes in the spleen and the head kidney were increased,after the addition of APS.Moreover,the spleen weight/body weight ratio was significantly increased in the0.15% addition group(P<0.05).In the liver,the level of T-AOC in the 0.10% APS addition group was significantly higher than that in the non-addition group,the 0.05% group and the0.15% addition groups.The CAT activity in the 0.05% addition group was significantly higher than that in the non-addition and the 0.10% supplemented groups,whereas the MDA content in the 0.10% addition group was significantly lower than that in the non-addition group(P<0.05).In the spleen,the levels of TNF-α in all APS addition groups were significantly increased,and the activity of lysozyme(LZM)in the 0.10% addition group was significantly enhanced than the non-addition group(P<0.05).Effects of APS addition on immune-related gene expression.The liver toll-like receptor8(TLR8)gene expression in the 0.10% APS addition group was significantly higher than that in the non-addition group,and the spleen TLR8 expression in the 0.05% addition group was also significantly increased(P<0.05).In addition,the gene expressions of laboratory of genetics and physiology 2(LGP2)and melanoma differentiation-associated gene 5(MDA5)in the liver from all APS addition groups were significantly higher than those in the non-addition group(P<0.05).Moreover,the expressions of x-box-binding protein 1(Xbp1)and cysteinylaspartate specific proteinase 2(Caspase-2)and Caspase-9,in the liver and spleen from all APS addition groups were significantly down-regulated than those in the non-addition group(P<0.05).The immune effects of APS addition against Aeromonas hydrophila infection.After the infection of Aeromonas hydrophila,the survival rates of the non-added group the 0.05%,the0.10% and the 0.15% APS addition groups were 14%,26%,22% and 42%,respectively;and the survival rates were all 100% in the control group those injected with normal saline.The symptom occurrence of fish was slower in the APS addition groups.Compared with the fish in the control group injected with physiological saline,the expression level of TLR8 gene in the spleen of the 0.15% APS addition group was significantly increased after infection(P<0.05).The gene expressions of LGP2 in the liver from the 0.05% and 0.15% APS addition groups and in the spleen from the 0.15% APS addition group were significantly up-regulated(P<0.05).In all of the APS addition groups,the expressions of MDA5 and Xbp1 in the liver and the spleen were significantly increased(P<0.05).The gene expressions of nucleotide-binding domain leucine-rich 1(NOD1)in the liver from 0.15% addition group,and the gene expressions of NOD2 in the spleen from 0.05% and 0.15% addition groups were significantly up-regulated(P<0.05),whereas the expression of Caspase-2 and Caspase-9 genes in the liver and the spleen from APS addition groups were all significantly down-regulated(P<0.05).In conclusion,the addition of APS to the diet can improve the growth performance of Furong crucian carp,and the addition of 0.05% APS is an appropriate ratio to promote the fish growth.The addition of APS can also enhance the immunity and resistance to Aeromonas hydrophila infection.The survival rate of Aeromonas hydrophila was the highest in the group that fed with 0.15% APS addition diet.The results from the present study provide scientific data for in-depth understanding of the comprehensive functional effects of APS on Furong crucian carp,and provide a basis and reference for the development and application of APS diets for fish. |
