Fffects Of Dietary α-lipoic Acid On Growth,Serum Biochemical Indexes,metabolism And Antioxidant Capacity Of Juvenile Largemouth Bass,Micropterus Salmoides

A 9-week feeding experiment was conducted to investigate the effects of dietaryα-lipoic acid（α-LA）on growth performance,serum biochemical indexes,metabolism and antioxidant capabilities in largemouth bass（Micropterus salmoides）.Four isonitrogenous（480 g/kg crude protein）and isolipidic（100 g/kg crude lipid）diets,which used defatted fish meal,casein and gelatin were as the main protein sources,rapeseed oil as the main lipid sources,were formulated to contain different levels of α-LA（0,200,400 and 800 mg/kg）at the expense of microcrystalline cellulose,respectively.Results showed that there were no significant differences in final weight（FW）,specific growth rate（SGR）,feed conversion rate（FCR）,protein efficiency ratio（PER）and condition factor（CF）（P>0.05）,while the intraperitoneal fat body index（IFI）were significantly reduced for fish fed diet at 800 mg/kg α-LA（P<0.05）.The lowest hepatosomatic index（HSI）and viscerosomatic index（VSI）was obtained at 200 and400 mg/kg（P<0.05）,respectively.The crude protein of muscle could be significantly increased by 400 mg/kg α-LA（P<0.05）,while the crude lipid was reduced by 400 and800 mg/kg（P<0.05）.Although the crude protein of fish body had no significant difference among the groups（P<0.05）.There was no significant difference in the ash and moisture of whole body and muscle among the groups（P>0.05）.WEB,RBC and HGB contents showed a somewhat increasing trend before showing a decreasing trend（P>0.05）;the highest level of WEB,RBC and HGB were observed in the group fed with a dietary α-LA level of 400 mg/kg（P>0.05）.The PLT were significantly increased with increasing of dietary α-LA from 0 to 200 mg/kg（P<0.05）,reached the highest levels at 400 mg/kg dietary α-LA,and then decreased at dietary LA（P<0.05）.There were no significant differences in NRU between groups fed with 200 and 800 mg/kg dietary available α-LA（P>0.05）.However,the maximal level of them could be observed in groups fed with dietary available α-LA（P<0.05）.Moreover,LYM and MON were increased significantly with the increase in dietary α-LA from 0 to 400 mg/kg（P<0.05）,with the further increase in dietary α-LA,no significant difference was observed（P>0.05）.The blood indices calculated from the mean values of blood parameters shows that HCT and MCH were no significantly differences（P>0.05）.Plasma glucose（GLU）,triglycerides（TG）,total cholesterol（TCH）and low-density lipoprotein cholesterol（LDL-C）contents were significantly lower at dietary α-LA levels of 800 mg/kg（P<0.05）,while concentration high-density lipoprotein cholesterol（HDL-C）,contents were significantly higher（P<0.05）.The contents of insulin（INS）,adiponectin（ADPN）,Apelin and Agouti-related protein（AGRP）in serum reached the maximum values when the supplemental level was 200mg/kg（P<0.05）.Leptin（LEP）and cholecystokinin（CCK）reached the maximum when the supplemental level was 400 mg/kg（P<0.05）.Hexokinase（HK）,phosphofructokinase（PFK）and pyruvate kinase（PK）in the liver were continuously increased to the highest levels in largemouth bass groups fed with 800 mg/kg dietary α-LA（P<0.05）.The activity of pyruvate dehydrogenase（PDH）in the liver increased significantly with the increase in dietary α-LA from 0 to 800mg/kg（P<0.05）.The activity of phosphoenolpyruvate carboxykinase（PEPCK）and glucose-6-phosphate（G6P）in the group fed with a dietary α-LA 800 mg/kg were significantly decreased（P<0.05）.Conversely,the activity of Phosphoenolpyruvate carboxykinase（PEPC）was significantly increased with increasing dietary α-LA levels from 400 to 800 mg/kg（P<0.05）.Moreover,carnitine palmitoyltransferase 1（CPT-1）,hormone-sensitive triglyceride lipase（HSL）and lipase（LPS）activities in the liver were increased with increasing of dietary α-LA contents from 0 to 200 mg/kg（P<0.05）,keep at a relative stable level from 200 to 400 mg/kg dietary α-LA levels（P>0.05）,and then increased at 800 mg/kg dietary α-LA（P<0.05）.However,the activity of acetyl-Co A carboxylase（ACC）was reduced as dietary α-LA levels decreased from 0 to 200 mg/kg（P<0.05）and then were decreased with a further decrease in dietary α-LA levels from400 and 800 mg/kg（P<0.05）.The gene expression levels of glucose transporter 2（GLUT2）,GS and glycogen protein1（GN1）in the liver increased with the addition of α-LA in the diet（P<0.05）.Similarly,the expression level of glycogen phosphorylase（GP）was significantly increased（P<0.05）,but the gene expression level of debranching enzyme（GDE）was significantly decreased（P<0.05）when the supplementation amount was 800 mg/kg.The expression levels of glycolysis key enzymes HK,PFK and PK increased with the increase of α-LA in the diet（P<0.05）.While the m RNA expression levels of PC,PEPCK and G6 P were reduced at 400 mg/kg dietary α-LA（P<0.05）.The highest level of GS and PDH were found in fish fed with a dietary α-LA level of 800 mg/kg.Moreover,the highest level of DAGL and MGL were observed in the group fed with a dietary α-LA level of 400 mg/kg（P<0.05）.Similarity,the m RNA expression levels of fatty acid binding protein（FABP）was significantly increased with increasing dietaryα-LA levels from 400 to 800 mg/kg（P<0.05）.Conversely,the m RNA expression levels of diacylglycerol O-acyltransferase 2（DGAT2）and sterol regulatory element binding transcription factor 2（SREBP-2）were significant reduced at 400 mg/kg dietary α-LA（P<0.05）.In addition,adequate dietary α-LA content（200,400,and 800 mg/kg）could significantly increase the activities of superoxide dismutase（SOD）,catalase（CAT）,glutathione reductase（GR）（P<0.05）.Similarly,adequate dietary α-LA content（200,400,and 800 mg/kg）could significantly improve glutathione（GSH）contents and total antioxidant capacities（T-AOC）in the liver of largemouth bass（P<0.05）.However,glutathione S-transferase（GST）activities and malondialdehyde（MDA）levels were significantly increased by excessive α-LA content（800 mg/kg）in the liver of largemouth bass（P<0.05）.In conclusion,the research indicated that the amount of α-LA（400-800 mg/kg）supplementation in the diet can decrease the crud lipid content of fish,promote glucose metabolism and relieve lipid oxidative damage by accelerating lipid catabolism and reducing lipid synthesis of juvenile largemouth bass.On the other hand,200-400 mg/kg dietary α-LA could increase the activity of antioxidant enzymes and enhance the antioxidant capacity of juvenile largemouth bass.