| In order to compare the effects of rapeseed meal and fermented rapeseed meal with different anti-nutritional factor contents on Litopenaeus vannamei（L.vannamei）,and to explore the role and function of isothiocyanate,a secondary metabolite of anti-nutritional factors,replacement of fishmeal by graded levels of rapeseed meal,fermented rapeseed meal with reduced isothiocyanate and the addition of propenyl isothiocyanate to feed was designed,and the growth,degestion,nutrient deposition,hepatopancreas health and immunity of L.vannamei were investigated.In addition,to further understand the effect of dietary isothiocyanate on growth in pratical feeding,the effects of rapeseed meal and fermented rapeseed meal with reduced isothiocyanate content substituting fishmeal on the hepatopancreas metabolism of L.vannamei were also investigated in this paper,exploring the metabolic mechanism of rapeseed meal or fermented rapeseed meal in feed acting on the growth of L.vannamei were analyzed through metabolomic analysis.1.Effects of rapeseed meal,fermented rapeseed meal and isothiocyanate on growth performance,digestibility and nutrient deposition of L.vannameiTo investigate the effects of dietary rapeseed meal,fermented rapeseed meal replacing fishmeal and dietary isothiocyanate on growth performance,digestibility and hepatopancreatic histology of L.vannamei,in experiment,in addition to the control group,four groups of 5%（R5）,10%（R10）,15%（R15）and 20%（R20）rapeseed meal and four groups of 5%（F5）,10%（F10）,15%（F15）and 20%（F20）fermented rapeseed meal replacing fishmeal were designed;In order to determine whether isothiocyanate affects the substitution of fish meal by rapeseed meal,other two groups（I10 and I20）of semi-purified feed supplemented with acrylic-isothiocyanate（ITC）were also designed,whose ITC content was the same as that in R10 and R20（51.7 mg/kg and 103.4 mg/kg）,respectively.The above 11 groups of isonitrogenous and isoenergetic（CP 41%,GE 17MJ/Kg）formulated diets were fed an initial average body weight of（3.0±0.3）g of L.vannamei for 8 weeks.Results showed:（1）Under the experimental conditions,rapeseed meal replacing fish meal within 20%reduced the feed coefficient,protein apparent digestibility and lipase activity（P<0.05）,but had no significant effect on the total amino acid content of muscle.10%rapeseed meal can maintain the normal form of prawn liver and pancreas,and more than 10%rapeseed meal would reduce the muscle protein content（P<0.05）.15%rapeseed meal did not affect the weight gain rate of the shrimp,but can improve the content of Ca and P of shrimp shells and improve the activity of trypsin（P<0.05）.（2）15%fermented rapeseed meal can reduce the feed coefficient,and not only it didn’t significantly improved the growth,nutrients,liver and pancreas morphology and other indicators;but also reduced protein apparent digestibility and lipase activity（P<0.05）compared with rapeseed meal.（3）Acryyl isothiocyanate supplemented with 103.4mg/kg alone had no significant effects on the growth and liver-pancreatic tissue morphology of shrimp compared with the control group and corresponding rapeseed meal group,but reduced the lipase activity（P<0.05）.Compared with the rapeseed meal groups,the addition of acryl isothiocyanate alone increased the protein apparent digestibility,and muscle protein content,and had a promoting effect on methionine deposition in shrimp（P<0.05）.These results indicated that the 15%replacement of fishmeal by rapeseed meal did not affect the normal growth of L.vannamei and improves protein digestion and utilization,but affected feed intake and fat absorption.Fermented rapeseed meal with reduced isothiocyanate had no effect on growth compared to rapeseed meal and improved feed utilization and protein digestion,but further reduced fat digestion.It is hypothesized that isothiocyanate in rapeseed meal may also be beneficial to protein deposition and fat metabolism in L.vannamei as isothiocyanate added alone,providing new ideas for the utilization of isothiocyanate in aquatic animals.And the inference needs further verification.2.Effects of rapeseed meal,fermented rapeseed meal and isothiocyanate on biochemical parameters,thyroid hormones,antioxidant capacity,immunity and expression of genes related to liver and intestinal health in L.vannameiIn order to investigate the effects of rapeseed meal,fermented rapeseed meal and isothiocyanate on the biochemical parameters,thyroid hormones,antioxidant capacity,immunity and gene expression related to liver and intestinal health of L.vannamei,the biochemical,antioxidant,immunological,liver and intestinal health related indices of L.vannamei were measured at the end of the culture experiment in the previous chapter.The results showed that:（1）The use of less than 20%rapeseed meal in the feed reduced serum TP,ALB,blood ammonia and BUN（P<0.05）;increased serum T-AOC and decreased MDA（P<0.05）;decreased hepatopancreas T-AOC and SOD;and up-regulated CYP4V18 gene（P<0.05）.The substitution of fishmeal within 20%did not affect the immunity level of shrimps,improved nitrogen utilization,antioxidant capacity of shrimp serum,and facilitated shrimp moult;however,it reduced protein absorption,antioxidant level of hepatopancreas and energy absorption.（2）In the 5%fermented rapeseed meal group,serum TP increased,blood ammonia decreased and TG and TC levels increased（P<0.05）,significantly improving the antioxidant capacity and hepatopancreas health of the shrimp.The increased serum C3and C4 concentrations and the down-regulation of anti-inflammatory factors such as My D88,TRAF6 and TGF-β1 in the shrimp indicated that FRM improved the immunity of the shrimp.20%of the FRM was used to suppress growth and damage the hepatopancreas of the shrimp,as evidenced by a decrease in albumin and an increase in blood ammonia,inhibited BUN and was detrimental to nutrient deposition in the shrimp organism;reduced T-AOC,GPx and antioxidant capacity.（3）The addition of less than 51.7 mg/kg of propenyl isothiocyanate had a negative effect on nitrogen uptake and fat absorption and metabolism in L.vannamei,but increased serum protein,triglycerides and cholesterol compared to the corresponding rapeseed meal group,speculating that isothiocyanate in rapeseed meal would interact with other substances and further affect the metabolism of protein and fat in shrimp.The addition of isothiocyanate less than 103.4 mg/kg increased the total antioxidant capacity,superoxide dismutase activity,glutathione peroxidase,malondialdehyde and C3 and C4,and improved the antioxidant capacity and non-specific immunity of shrimps;based on the results of oxidative gene expression,it suggested that the addition of isothiocyanate can reduce the risk of antioxidant damage in the hepatopancreas.3.Metabolomics-based study on mechanism of action of rapeseed meal and fermented rapeseed meal on growth and hepatopancreas health of L.vannameiBased on the results of growth performance and hepatopancreas health in Chapter 1 and 2,LC-MS metabolomics was further applied to analyze the hepatopancreas metabolites of the Control,R15 and F15 groups to investigate the mechanism of the effect of rapeseed meal and isothiocyanate-reduced fermented rapeseed meal on L.vannamei,and from the side to understand the effect of the antinutritional factor isothiocyanate in rapeseed meal on the hepatopancreas metabolism of L.vannamei through the comparison between the F15 and R15 groups.The results showed that:（1）There were 898 differential metabolites in the hepatopancreas of L.vannamei in the R15 group compared to the Control group,of which 39 differential metabolites were annotated to the KEGG database,including 7 up-regulated metabolites and 32 down-regulated metabolites.12 metabolic pathways were significantly different（P<0.05）,namely One carbon pool by folate,Purine metabolism,Aminoacyl-t RNA biosynthesis,Biosynthesis of unsaturated fatty acids,Fox O signaling pathway,Arachidonic acid metabolism,Pyrimidine metabolism,Histidine metabolism,Alanine,aspartate and glutamate metabolism,Linoleic acid metabolism,Glycerophospholipid metabolism,Phenylalanine,tyrosine and tryptophan biosynthesis.（2）There were 1141 differential metabolites in the hepatopancreas of L.vannamei in the F15 group compared to the Control group,of which 50 differential metabolites were annotated to the KEGG database,including 15 up-regulated metabolites and 35 down-regulated metabolites.8 metabolic pathways were significantly different（P<0.05）,namely Purine metabolism,Pyrimidine metabolism,Aminoacyl-t RNA biosynthesis,Alanine,aspartic and glutamate metabolism,Fox O signaling pathway,Biosynthesis of unsaturated fatty acids,Linoleic acid metabolism,D-Glutamine and D-glutamate metabolism.（3）There were 994 differential metabolites in the hepatopancreas of L.vannamei in the F15 group compared to the R15,of which 50 differential metabolites were annotated to the KEGG database,including 23 up-regulated metabolites and 27 down-regulated metabolites.11 metabolic pathways were significantly different,namely Purine metabolism,Aminoacyl-t RNA biosynthesis,Pyrimidine metabolism,Alanine, aspartate and glutamate metabolism,Histidine metabolism,Fox O signaling pathway,Glycerophospholipid metabolism,One carbon pool by folate,ABC transporters,Glycine,serine and threonine metabolism,D-Glutamine and D-glutamate metabolism.The above results indicated that 15% replacement of fishmeal by rapeseed meal in the feed had a significant effect on the metabolism of L.vannamei,and promoted growth and development from the metabolic level of the shrimp,enhanced the absorption and utilization of amino acids and other nutrients in the shrimp organism,but relatively reduced the freshness of the shrimp muscle;promoted fat metabolism,reduces fat accumulation in the hepatopancreas;improved the anti-inflammatory effect of the shrimp and protected the health of the shrimp hepatopancreas.The replacement of fishmeal by fermented rapeseed meal with reduced isothiocyanate also had a significant effect on the hepatopancreas metabolism of L.vannamei.15% fermented rapeseed meal was more beneficial than 15% rapeseed meal in promoting growth and protein uptake in shrimp,but it reduced nerve signalling and lipid metabolism,which was detrimental to the hepatopancreas health of L.vannamei.It is assumed that isothiocyanate in 15% rapeseed meal is beneficial to the hepatopancreas of L.vannamei,but the exact functional mechanism needs to be further investigated. |
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