| Aquatic animals cannot synthesize vitamin A by themselves and need to rely on food for vitamin A or its precursors-carotenoids.At present,there is no report on vitamin A requirement of Monopterus albus.In this study,we used M.albus of small size(2.64 g),medium size(7.32 g)and large size(85.41 g)as materials,and vitamin A acetate as supplemental source of vitamin A,and evaluated the vitamin A requirement of M.albus by growth performance,biochemical indexes,hepatointestinal tissue structure and transcriptome.The main results are as follows:1.Small size Monopterus albus vitamin A requirementsSeven isonitrogenous and isoenergetic experimental diets were prepared by adding vitamin A acetate into the basal diet(The measured content is 2 910、3 230、3 520、3840、5 020、7 030 、11 800 IU/kg),numbered X1-X7,and the incubation period was 56 days.Results:(1)The FBW,WGR and SGR of M.albus in X3 group were significantly higher than those in X1 group(P<0.05),and there was no significant difference in FCR(P>0.05).(2)The activities of GPT and GOT in serum of X1 and X7 groups were significantly higher than those of X3-X5(P<0.05).(3)The liver cells of X1,X6 and X7 groups were enlarged and most of the nuclei disappeared.The liver cells of X6 and X7 groups were vacuolated.2.Medium size Monopterus albus vitamin A requirementsSeven isonitrogenous and isoenergetic experimental diets were prepared by adding vitamin A acetate into the basal diet(The measured content is 3 201、3 620、4 010、4730、6 510、9 720、16 890 IU/kg),numbered Z1-Z7,and the incubation period was 70 days.Results:(1)The FBW,WGR and SGR of M.albus in Z2-Z4 groups were significantly higher than those in Z1 and Z7 groups(P<0.05).There was no significant difference in FCR(P>0.05).(2)The crude fat content of whole fish in Z1 and Z2 groups decreased significantly(P<0.05).(3)The contents of liver TG and T-CHO in Z3-Z5 groups were significantly decreased(P<0.05).(4)Serum GLU in Z3-Z5 groups was significantly higher than that in other groups(P<0.05).The content of serum insulin in Z1 and Z2 groups was significantly higher than that in Z3-Z7 groups(P<0.05).(5)Serum TAOC decreased and MDA content increased in Z7 group.There was no significant difference in SOD and cat activities in each group.The serum LZM activity in Z2-Z4 group was significantly higher than that in Z7 group(P<0.05).(6)The amylase activity of hepatopancreas in Z2 group was the highest,which was significantly higher than that in Z6 and Z7 groups(P<0.05);Z3 group had the highest protease activity in hepatopancreas,stomach and foregut;The lipase activity of hepatopancreas and foregut in Z5 group was the highest.(7)The VH,MH and LW of foregut in Z3 group were significantly higher than those in Z1 group(P<0.05),and there was no significant difference between Z2 and Z4groups(P>0.05).3.Large size Monopterus albus vitamin A requirementsFive isonitrogenous and isoenergetic experimental diets were prepared by adding vitamin A acetate into the basal diet(The measured content is 3 510、4 350、5 160、6930、10 600 IU/kg),numbered D1-D5,and the incubation period was 100 days.Results:(1)The FBW,WGR and SGR of M.albus in D2 and D3 groups were significantly higher than those in other groups(P<0.05),but FCR was not significantly different(P>0.05).(2)Serum GLU and insulin contents in D3-D4 groups were significantly decreased(P<0.05).(3)The activities of T-AOC and CAT in D5 group were the lowest,and the content of MDA was the highest.Serum LZM activity in D3 and D4 groups was significantly higher than that in D1 and D5 groups(P<0.05).(4)The activities of amylase,protease and lipase in group D3 were significantly higher than those in group D1,D4 and D5(P<0.05);The lipase activities in the stomach,foregut and hindgut were higher in D3-D5 groups.4.Regulation mechanism of Vitamin A on lipid metabolism of Monopterus albusThe livers of M.albus in Z1,Z4 and Z7 groups were taken for transcriptome analysis and renumbered as A,D and G to explore the mechanism of vitamin A regulating lipid metabolism in M.albus.Results:(1)With the rise of vitamin A content,the number of differential genes connected to lipid metabolism increased from 12 to 24,and the number of substantially enriched pathways also increased from 1 to 3.(2)Trend analysis revealed that plpp1 a,plpp2b and cyp21a2 genes were continuously up-regulated with the rise of vitamin A content in feed;akr1d1,ugt1a1 and cyp1 a genes were down regulated continuously.Conclusion:(1)Taking WGR as the evaluation index,it is concluded that the appropriate vitamin A requirements of small-sized,medium-sized and large-sized M.albus are 3 482、3 856 and 4 847 IU/kg respectively.The comprehensive growth performance,serum biochemistry,digestive enzyme activity and other indicators indicate that the demand is 3 230-5 020、3 620-4 730 and 4 350-5 160 IU/kg respectively.(2)It is speculated that vitamin A promotes the synthesis of lipids in the body by enhancing phosphatase activity,and decreases the metabolism of lipids by governing bile acids and cholesterol,resulting in the increase of crude fat in the whole fish.(3)When vitamin A was lower than 2 910 IU/kg,it was not conducive to the growth of M.albus;When it exceeds 7 030 IU/kg,it may affect the liver function of small-size M.albus;When more than 16 890 IU/kg,the antioxidant capacity,immune capacity,liver function and digestive enzyme activity of medium-size M.albus decreased,which was not conducive to the development of its foregut and slowed down its growth.Vitamin A exceeding 10 600 IU/kg will reduce the antioxidant capacity and immunity of large-size M.albus and slow down its growth. |
