| An 8-week feeding trial was conducted to investigate the effects of dietary selenium levels on the growth performance,glycolipid metabolism and antioxidant capacity,and the relaxation effects of bamboo charcoal on dietary excessive selenium in juvenile blunt snout bream(Megalobrama amblycephala).The juvenile blunt snout bream(16.0±0.5 g)were randomly distributed to 36 tanks(diameter 820 mm,height 700 mm)with a density of 20 fish per tank.Nine experimental diets were prepared selecting fish meal,soybean meal,rapeseed meal,cottonseed meal and wheat flour were selected as ingredients,of which 5 diets were gradually added sodium selenite 0 mg/kg,0.6 mg/kg,1.3 mg/kg,2.7 mg/kg and 4.0 mg/kg(the selenium content was 0.103 mg/kg,0.420 mg/kg,0.667 mg/kg,1.055 mg/kg and 1.464 mg/kg),and the other four groups were added with 4.0 mg/kg of sodium selenite(the selenium content is 1.561 mg/kg,1.399 mg/kg,1.391 mg/kg,and 1.395 mg/kg)and gradient bamboo charcoal of 1 g/kg,2 g/kg,3 g/kg and 4 g/kg.The main contents of this study included the following 4 parts:1 Dietary selenium requirement of juvenile blunt snout breamIn this study,the juvenile blunt snout bream were fed with five diets inclusion of 0.103,0.420,0.667,1.055 and 1.464 mg Se/kg diet for 8 weeks.The results showed that dietary selenium of 0.67-1.06 mg/kg improved final body weight(FW),weight gain rate(WGR)and specific growth rate(SGR),and reached the maximum in the Sel.06 group(p<0.05),and then showed a downward trend.The feed coefficient(FCR)showed the opposite trend,decreased with the increasing dietary selenium(p<0.05),reaching the minimum FCR in the Sel.06 group,and the dietary selenium levels did not affect the viscerosomatic index(VSI)(p>0.05).Se deposition in muscle was increased(p<0.05)in the groups fed selenium equal or higher than 0.67 mg/kg,but moisture,protein,lipid and ash content were not affected(p>0.05).The plasma total protein and albumin(ALB)contents were highest in fish fed with 1.06 mg/kg dietary selenium(p<0.05),while the plasma cholesterol(TC)shown the lowest value(p<0.05).The optimum dietary selenium levels were 0.959 and 0.958 mg/kg respectively based on SGR and WGR with the best SGR of 1.798%/day and the best WGR of 173.852%(p<0.05).2 Different dietary selenium affected the glucosemetabolism and lipid metabolism inthe liver of juvenile blunt snout breamAfter the juvenile blunt snout bream were being fed with five diets inclusion of 0.103,0.420,0.667,1.055 and 1.464 mg Se/kg diet for 8 weeks,the genes related to glucose metabolism(including glycolysis and gluconeogenesis)and lipid metabolism in the liver were evaluated.The results showed the relative expression of glucose metabolism-related gene glucokinase(GK)was significantly reduced when dietary selenium inclusion level was 1.46 mg/kg(p<0.05);the relative expression of glucose-6-phosphate(G6P)gene was significantly increased with dietary selenium supplemented of 1.06-1.46 mg/kg(p<0.05).The gene expression levels of phosphoinositide 3-kinase(PI3K)and phosphoenolpyruvate carboxykinase(PEPCK)was presented to be the highest while dietary selenium was supplemented of 1.06 mg/kg(p<0.05),butthe gene expression of pyruvate kinase(PK)and glycogen synthase(GS)were not affected by dietary selenium(p>0.05).The expression levels of lipid metabolism-related genes,fatty acid synthase(Fas),acetyl-CoA carboxylase(ACC)and cholesterol 7α-hydroxylase(CYP7A1),increased while dietary selenium levels were equal or higher than 1.06 mg/kg(p<0.05).In contrast,the expression level of 33-hydroxy-3-methylglutaryl-CoA reductase(HMGCR)was the lowest in the group of 1.06 mg Se/kg diet(p<0.05)3 Different dietary selenium affects the antioxidant capacity and immunity in the liver of juvenile blunt snout breamAfter the juvenile blunt snout bream were being fed with five diets inclusion of 0.103,0.420,0.667,1.055 and 1.464 mg Se/kg diet for 8 weeks,the activities of antioxidant enzymes and the expression of genes related to antioxidant and immune in the liver were evaluated.The results showed that the activities of catalase(CAT),total superoxide dismutase(T-SOD),reduced glutathione(GSH)and glutathione peroxidase(GSH-Px)were increased in fish fed dietary selenium of 1.06 mg/kg(p<0.05).In contrast,the activities of malondialdehyde(MDA)was significantly inhibited with dietary selenium of 0.67-1.06 mg/kg(p<0.05).Meanwhile,the gene expression levels of copper-zinc superoxide dismutase(Cu/Zn-SOD),Kelch-like ECH-associated protein 1(Keap 1),nuclear factor erythroid 2-related factor 2(Nrf-2),CAT and GSH-Px were significantly improved in fish fed dietary selenium of 1.06 mg/kg(p<0.05).However,the gene expression level of manganese superoxide dismutase(Mn-SOD)in the liver was not affected by dietary selenium(p>0.05).In addition,when the dietary selenium was 1.06 mg/kg,the expression level of the nuclear factor-kappa B(NFκB)was suppressed(p<0.05);a higher level of dietary selenium(0.67-1.46 mg/kg)significantly inhibited the expression levels of interleukin 8(IL-8),transforming growth factor-β(TGF-β)and tumor necrosis factor-α(TNF-α)genes(p<0.05).4 The relaxation effect of bamboo charcoal on dietary excessive seleniumIn order to study the relaxation effect of bamboo charcoal on excessive selenium in the diet of juvenile blunt snout bream,five high-selenium dietswith graded bamboo charcoal levels of 0 g/kg(Se 1.464 mg/kg,BC 0 g/kg),1 g/kg(Se 1.561 mg/kg,BC 1 g/kg),2 g/kg(Se 1.399 mg/kg,BC 2 g/kg),3 g/kg(Se 1.391 mg/kg,BC 3 g/kg)and 4 g/kg(Se 1.395 mg/kg,BC 4 g/kg)were prepared and fed to fish 8 weeks.The growth performance,biochemical indexes,muscle nutrients and antioxidant capacity were evaluated.The results showed that when the inclusion level of bamboo charcoal in high-selenium diets was 0-3 g/kg,WGR and SGR were significantly improved with the increasing levelof bamboo charcoal,and VSI was not affected by the bamboo charcoal inthe high-selenium diet(p>0.05).The inclusion level of high-selenium diets didn’t influence the muscle moisture,lipid and ash of juvenile blunt snout bream(p>0.05).The muscle protein was highest in the fish fed the high-selenium diet supplemented with 1 g/kg bamboo charcoal(p<0.05).The content of selenium in muscle decreased significantly with the increasing amount of bamboo charcoal(p<0.05).When the inclusion level of bamboo charcoal in high-selenium dietswas 3g/kg,the plasma glucose(GLU)and ALB were the highest(p<0.05),and the alkaline phosphatase(ALP)was thelowest(p<0.05).The activities of total antioxidant capacity(T-AOC),CAT,T-SOD and GSH-Px(p<0.05)were significantly increased in fish fed with 3 g/kg bamboo charcoal in the high-selenium diet.MDA activity in the liver significantly decreased in fish fed with 3-4 g/kg bamboo charcoal levels of high-selenium diets(p<0.05).GSH activity in the liver was not affected by bamboo charcoal level(p>0.05).Meanwhile,the expressions of GSH-Px,Keap 1,Mn-SOD,Nrf-2 and CAT were activated in fish fed with 3 g/kg bamboo charcoal of high-selenium diet(p<0.05).However,the expression level of Cu/Zn-SOD was not significantly affected by bamboo charcoal level(p>0.05). |
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