Effects Of Selenium-rich Cardamine Hupingshanensis On Growth,Metabolism,and Immunity In Juvenile Black Carp（Mylopharyngodon Piceus）

The experiment aims to investigate the effects of different levels of dietary selenium-rich Cardamine hupingshanensis on the growth performance,physiological and biochemical parameters,selenium metabolism,antioxidant capacities,innate immunities and glucose metabolism in black carp（Mylopharyngodon piceus）,in order to lay a theoretical foundation for the development of compound feeds for juvenile black carp.360 juvenile black carps with initial body weight of（5.51±0.02）g were randomly divided into four groups,and each group had 3 replicates.Four levels of selenium-rich C.hupingshanensis（0,0.5,1.0,2.0 g/kg）（selenium levels 0.04,0.43,0.75,1.57 mg/kg）were added and made four isonitrogenous and isoenergetic diets.The culture period was conducted for 60 days.The results showed are as follows:Dietary selenium-rich C.hupingshanensis levels had significant effects on final body weight（FBW）,weight gain rate（WG）,specific growth rate（SGR）and feed conversion ratio（FCR）of juvenile black carp（P<0.05）.However,there were no significant differences in the hepatosomatic ratio（HSI）,condition factor（CF）,survival rate,moisture and ash contents of juvenile black carp among all groups（P>0.05）.The supplementation of selenium-rich C.hupingshanensis could increase the crude protein contents,and the maximum value was reached at 1.0 g/kg dietary selenium-rich C.hupingshanensis（P<0.05）.In the serum,triglyceride（TG）,total cholesterol（TCH）and albumin（ALB）contents were increased with increasing dietary selenium-rich C.hupingshanensis levels from 0.5 to 1.0 g/kg dietary selenium-rich C.hupingshanensis（P<0.05）,while the content of glucose（GLU）was significantly decreased（P<0.05）.In addition,adequate supplemental level of selenium-rich C.hupingshanensis significantly increase expression level of selenium-metabolic proteins,including selenocysteine lyase（SCLY）,selenide,water dikinase 1（SPS1）,15 k Da selenoprotein（SEP15）,selenoprotein T2（SEPT2）,selenoprotein H（SEPH）,selenoprotein P（SEPP）in the liver of juvenile black carp compared with the control group（0 g/kg）（P<0.05）.Dietary supplementation of 0.5-1.0 g/kg selenium-rich C.hupingshanensis significantly increased the relative gene expression level of nuclear factor E2-related factor 2（Nrf2）in the liver,while the relative gene expression level of Kelch-like ECH associated protein 1（keap1a and keap1b）was significantly decreased（P<0.05）.The mRNA expression levels of Mn-superoxide dismutase（Mn-SOD）,catalase（CAT）,glutathione peroxidase 1（GPX1）and glutathione peroxidase 4（GPX4）in the liver were significantly increased by 0.5-1.0 g/kg dietary selenium-rich C.hupingshanensis.GST-A’s expression levels were significantly decreased at 0.5 g/kg dietary seleniumrich C.hupingshanensis（P<0.05）.There were no significant differences in mRNA expression levels of Cu/Zn-superoxide dismutase（Cu/Zn-SOD）,glutathione stransferase M（GST-M）and glutathione reductase（GR）in fish fed with these experimental diets in this study（P>0.05）.Meanwhile,adequate dietary selenium-rich C.hupingshanensis levels（0.5-1.0 g/kg）could increase the activities of superoxide dismutase（SOD）,catalase（CAT）and improve glutathione（GSH）contents and total antioxidant capacities（T-AOC）in the liver of black carp（P<0.05）.2.0 g/kg dietary selenium-rich C.hupingshanensis could significantly downregulate the mRNA expression levels of antibacterial peptide 2a（Leap2a）in the liver of black carp juveniles（P<0.05）.Furthermore,the expression level of innate immune defense molecules,including liver-expressed antimicrobial peptide 2（Leap2）,hepcidin（HEPC）,lysozyme（LYS）and complement 3（C3）were significantly upregulated by adequate supplemental level of selenium-rich C.hupingshanensis（P<0.05）.The maximal mRNA expression levels of glucokinase（GK）,in the liver were obtained in groups fed 1.0 g/kg dietary selenium-rich C.hupingshanensis compared with the control group（0 g/kg）and excess group（2.0 g/kg）（P<0.05）.However,there were no significant differences on phosphofructokinase（PFK）and pyruvate kinase（PK）mRNA expression levels（P>0.05）.The mRNA expression levels of glucose-6-phosphate（G6Pase）,fructose-1,6-diphosphate（FBP）and phosphoenolpyruvate carboxykinase（PEPCK）were decreased and achieved the minimal levels at 1.0 g/kg dietary selenium-rich C.hupingshanensis,respectively,and then induced at 2.0 g/kg dietary selenium-rich C.hupingshanensis（P<0.05）.0.5-1.0 g/kg dietary selenium-rich C.hupingshanensis could significantly increase the activities of GK and HK in the liver;and the content of glycogen in the liver and muscle of black carp（P<0.05）.The activities of PFK and PK in the liver were continuously raised with increasing of dietary selenium-rich C.hupingshanensis levels（P<0.05）.The activity of lactate dehydrogenase（LDH）and the content of pyruvate could be significantly increase of1.0 g/kg dietary selenium-rich C.hupingshanensis,but the lactic acid（LD）content was significantly higher at 0.5 g/kg dietary selenium-rich C.hupingshanensis than that of the excess group（2.0 g/kg）（P<0.05）.The activities of PEPC,PEPCK and G6 Pase in the liver were not significantly different among the groups（P>0.05）.H＆E staining and Oil red O staining results showed that dietary selenium-rich C.hupingshanensis could improve the vacuolation phenomenon of hepatopancreases cells,and dietary with 0.5-1.0 g/kg selenium-rich C.hupingshanensis could significantly increase the number and area of lipid droplets in the liver（P<0.05）.In conclusion,these results suggest that the adequate dietary supplemental level of selenium-rich C.hupingshanensis could significantly increase growth performances,promote the selenium metabolism,improve antioxidant and glucose metabolism capacities and enhance innate immunities in black carp.