Effects Of Curcumin Supplementation In Low-fish Meal Diet On Growth Performance,Feed Utilization And Intestinal Health Of Yellow Drum(Nibea Albiflora)

Low-fish meal diet can lead to decline of fish growth performance and intestinal injury.It is one of the effective means to repair the intestinal injury induced by low-fish meal diet through nutritional regulation.Curcumin is an emerging green functional additive.In this study,the effects of fish meal replacement with different proportions of soybean meal on growth performance,feed utilization and intestinal health of yellow drum(Nibea albiflora)were firstly determined,and the repair effects of curcumin addition to soybean meal diet on growth and intestinal injury of N.albiflora were further explored,in order to provide nutritional sustained-release strategy for intestinal injury of N.albiflora induced by soybean meal.The main experimental contents and results were as follows:Experiment 1: Effects of different proportions of soybean meal in feed instead of fish meal on growth performance,feed utilization and intestinal health of N.albifloraAn 8-week feeding trial was conducted to explore the effect of different proportions of soybean meal replacing fish meal on the growth performance and intestinal health of N.albiflora.A basal diet which contained fish meal,casein and flour as the main protein sources,and fish oil,soybean oil and soybean lecithin as the main lipid sources was formulated.Three isonitrogenous and isolipidic experimental diets were formulated by replacing 0%(FM),50%(SBM50)and 100%(SBM100)fish meal protein with soybean meal protein on the basal diet.A total of 255 juvenile yellow drum with initial body weight of(8.42 ± 0.12)g were randomly assigned to 3 groups,with 3 replicates in each group.The results showed as follows: Compared with the FM group,survival rate and feeding rate of fish in SBM100 group decreased and increased significantly,respectively(P < 0.05).The weight gain rate(WGR)of fish fed SBM50 and SBM100 diets were significantly lower than that of fish fed FM diet.The specific growth rate(SGR),condition factor(CF)and crude protein content of fish body(P < 0.05),and feed coversion rate(FCR)of fish fed SBM50 and SBM100 diets were significantly increased(P < 0.05).The results of intestinal tissue sections showed that the intestinal villi in the SBM50 group shrank,while the intestinal villi in the SBM100 group shrank more,and the top of the villi fell off and broke.The m RNA expression of intestinal cytoskeleton(f-actin and arp2/3),anti-inflammatory cytokines(il-10 and tgf-β)and tight junction(claudin3,claudin4,occludin and zo1)in N.albiflora was significantly decreased(P < 0.05)with the increasing of soybean meal replacement ratio,while the m RNA expression of pro-inflammatory cytokines(il-1,il-6and tnf-α)was significantly increased(P < 0.05).In conclusion,the substitution of fish meal with high proportion of soybean meal in diets will reduce the growth performance and feed utilization rate,and aggravate intestinal health injury of N.albiflora.Experiment 2: Effects of curcumin in soybean meal diet on growth performance,feed utilization and intestinal health of N.albiflora.Our previous study proved that soybean meal diet can lead to growth performance reduction and intestinal health injury of N.albiflora.In this study,fish meal diet was used as positive control group(FM),and soybean meal replaced 50% fish meal protein group was used as negative control group(SBM50).On the basis of SBM50 diet,four different levels of curcumin(0.01%,0.02%,0.04% and 0.06%)were added as treatment groups,labeled as SBMC(0.01%),SBMC(0.02%),SBMC(0.04%)and SBMC(0.06%),respectively.360 juvenile N.albiflora with an initial body weight of(9.74± 0.12)g were selected and randomly assigned to 6 groups,with 3 replicates in each group,The feeding trail lasted for 8 weeks.The WGR and SGR of fish fed FM,SBMC(0.01%)and SBMC(0.02%)diets were significantly higher than those of fish fed other groups(P < 0.05);FR of fish fed SBM50 diet was significantly higher than that of fish fed FM,SBMC(0.01%),SBMC(0.02%)and SBMC(0.04%)diets(P < 0.05).The FCR of fish fed FM,SBMC(0.02%)and SBMC(0.04%)diets was significantly lower than that of fish fed SBM50 and SBMC(0.06%)diets(P < 0.05).The results of electron microscopy showed that the intestinal structure of fish fed FM diet was complete,the cells were arranged in an orderly manner,and the epithelial microvilli were neatly arranged,while the epithelial microvilli were broken and fell off in the SBM50 group;The intestinal microvilli of SBMC(0.02%)group were arranged neatly and densely,while the intestinal microvilli of SBMC(0.01%),SBMC(0.04%)and SBMC(0.06%)groups were sparse and the cells were disordered.The gene expression levels of cytoskeleton(f-actin and arp2/3),antiinflammatory factor(tgf-β)and tight junctions(claudin3,claudin4 and occludin)of fish fed SBM50 diet were significantly lower than those of fish fed FM diet(P < 0.05),while pro-inflammatory cytokines(il-1,il-6 and tnf-α)and apoptosis(caspase-1 and caspase-8)of fish fed FM diet were significantly higher(P < 0.05);Curcumin supplementation increased the m RNA expression levels of cytoskeleton(f-actin and arp2/3),antiinflammatory cytokines(il-10 and tgf-β),tight junction proteins(claudin3,claudin4,occludin and zo1)(P < 0.05),and decreased the m RNA expressions of pro-inflammatory factors(il-1,il-6 and tnf-α)and apoptosis(caspase-1 and caspase-8)at the same time(P <0.05).These results suggest that curcumin may alleviate low fish meal-induced intestinal injury by increasing the expression of cytoskeleton,tight junction genes and reducing the expression of pro-inflammatory cytokines and apoptosis genes.Overall,the optimum addition amount of curcumin in the soybean meal diet of yellow drum was 0.02%.Experiment 3: The repair effect analysis of curcumin on low fish meal-induced intestinal injury in N.albiflora.In order to further explore the repair effect of curcumin on low fish meal-induced intestinal injury of N.albiflora,a comparative experiment was conducted on the repair effect of curcumin and fish meal feeding effect.Three isonitrogenous and lipid diets,FM,SBM50 and SBMC(0.02%)were prepared.A total of 360 N.albiflora with initial body weight of(7.00 ± 0.01)g were selected and divided into 4 groups with 3 replicates per group.In the first four weeks,2 groups(6 replicates)were fed SBM50 diet,and the 2groups of which were fed FM and SBMC(0.02%)diet in the last four weeks,which were labeled as SBM50-FM and SBM50-SBMC(0.02%),respectively.The other two groups were fed FM and SBMC(0.02%)diet,respectively.The results showed as follows: Before the transfer feeding treatment,on 28 d,compared with the FM group and the SBMC(0.02%)group,body weight(BW),WGR,SGR,CF and intestinal weight(IW)of fish fed SBM50 diet were significantly reduced.Intestinal villi of fish fed SBM50 diet were significantly shrunk,and the height of intestinal villi and thickness of muscle layer were significantly decreased(P < 0.05).The m RNA expressions of intestinal cytoskeleton(factin and arp2/3),anti-inflammatory factors(il-10)and tight junctions(claudin3,occludin and zo1)were significantly decreased(P < 0.05).After feeding transfer treatment,on 56 d,the BW,WGR,SGR,CF and intestinal villus height of SBM50-FM group were significantly higher than those of SBM50-SBMC group(0.02%)(P < 0.05).The WGR and SGR of SBM50-FM group were significantly higher than those of FM group(P < 0.05),indicating the growth compensation effect of fish meal.what is noticeable is that BW and CF in the SBM50-SBMC(0.02%)group were significantly lower than those in the SBM50-FM group(P < 0.05),and there was no significant difference in intestinal body index between SBM50-SBMC(0.02%)and SBM50-FM(P > 0.05);Compared with the SBM50-FM group,the SBMC(0.02%)group had no significant difference in BW and CF(P > 0.05),while the intestinal body index was significantly higher(P < 0.05),suggestting that the repairing effect of curcumin in promoting the growth of yellow drum may be timedependent.The height of intestinal villi and the thickness of the muscle layer in the SBM50-SBMC(0.02%)group were significantly lower than those in the FM group(P <0.05),while the height of the intestinal villi and the thickness of the muscle layer in the SBMC(0.02%)group were not significantly different from those in the FM group(P >0.05),suggestting that the repair effect of curcumin on intestinal structure may also be time-dependent.After feeding transfer,fish meal and curcumin significantly up-regulated the m RNA expression of intestinal cytoskeleton(f-actin and arp2/3),anti-inflammatory cytokines(il-10)and tight junction protein(claudin3,claudin4,occludin and zo1),and down-regulated the gene expression of pro-inflammatory cytokine(il-6)on 56 d.These results indicated that adding curcumin to the diet could repair the food-borne injury caused by low fish-meal by increasing the expression of cytoskeleton and tight junction genes in the intestinal tract and improving the expression of inflammatory factors of yellow drum.