| An 8-week feeding trial was carried out to evaluate the effects of dietary arginine levels on growth performance,immunity and mucosal barrier in Lateolabrax maculatus reared at different water temperatures(33℃ and 27℃).Using fish meal and corn gluten as main protein source,six isonitrogenous and isolipid diets were formulated with 1.16%,1.65%,2.04%,2.44%,2.98%and 3.36%arginine,respectively.Quadruplicate groups(30 fish per replicate)of spotted seabass(2.90±0.05 g)were fed the test diets twice daily.The main results were as follows:(1)Effects of dietary arginine on growth and body composition of L.maculatus reared at different water temperaturesThe results demonstrated that growth and feed utilization were significantly influenced by both dietary arginine level and water temperature(P<0.05),but there was no interaction effect(P>0.05).The final body weight(FBW),weight gain rate(WGR),specific growth rate(SGR),feed efficiency(FE)and protein efficiency(PER)of spotted seabass reared at 33℃ were significantly lower than that reared at 27℃,but the CF was significantly higher than that reared at low water temperature(P<0.05).The survival rate(SR)was not affected by water temperature and arginine level(P>0.05).FBW,WGR and SGR of juvenile spotted seabass increased first and then decreased with the increase of dietary arginine level,and their maximum values appeared in Arg2.04 group(P<0.05).FE and PER increased significantly with the increase of dietary arginine level(P<0.05).When the dietary arginine level was higher than 2.04%,it remained stable.The HSI and VSI decreased first and then increased with the increase of dietary arginine level,and the minimum value of HSI and VSI appeared in Arg2.44 group(P<0.05).The CF was not affected by the dietary arginine level(P>0.05).Body composition analysis showed that high water temperature only significantly decreased the crude lipid content of spotted seabass(P<0.05),but had no effect on the moisture,crude protein and ash(P>0.05).With the increase of dietary arginine level,the moisture content of seabass decreased firstly and then increased,and the lowest moisture was observed in Arg2.44 group.On the contrary,the crude protein,crude lipid and ash content increased first and then decreased,and the maximum value was observed in the Arg2.44 group.A quadratic regression analysis based on WGR showed that the dietary arginine requirement of juvenile spotted seabass was 2.40%(5.32%dietary protein)in 33℃,while the dietary arginine requirement of juvenile spotted seabass was 2.47%(5.49%dietary protein)in 27℃.(2)Effects of dietary arginine on mucosal barrier function of L.maculatus reared at different water temperaturesThe dietary arginine level and water temperature significantly affected the gill superoxide dismutase(SOD)activity and malondialdehyde(MDA)content of spotted seabass(P<0.05),and there was a significant interaction(P<0.05).The activity of GSH-PX and SOD in 33℃ group was significantly lower than that in 27℃ group(P<0.05),while the MDA content was significantly higher than that in 27℃ group(P<0.05).The gill SOD activity increased first and then decreased with the increase of dietary arginine level(P<0.05),and reached the maximum value in Arg2.04 group.The activity of GSH-PX in gill of spotted seabass increased significantly with the increase of dietary arginine level(P<0.05).When the dietary arginine level exceeded 2.04%,there was no significant change in gill GSH-PX activity(P>0.05).The content of MDA in the gill of spotted seabass decreased first and then increased with the increase of dietary arginine level,and the minimum value appeared in Arg2.44 group(P<0.05).Analysis of gill tight junction protein gene expression showed that the expression of gill ZO-1,Occludin and Claudin b in 33℃ group was significantly lower than that in 27℃ group(P<0.05).The expression levels of Occludin and Claudin b increased first and then decreased with the increase of dietary arginine level.When the dietary arginine level was 2.44%,the gene expression levels of Occludin and Claudin b were the highest(P<0.05).Dietary arginine level had no significant effect on ZO-1 gene expression level(P>0.05).Analysis of the expression of intestinal inflammatory factor contents and gene expression in spotted seabass showed that water temperature and dietary arginine levels significantly affected the intestinal inflammatory genes IL-1β,IL-6,IL-10,IL-4 and TNF-α levels,and there was a significant interaction(P<0.05).The levels of intestinal IL-4,IL-10 and NF-κB in 33℃ group were significantly lower than that in 27℃ group,while the IL-1β,IL-6,TNF-α levels,TLR4 and MAPKp38 expression levels were significantly higher than that in 27℃ group(P<0.05).With the increase of dietary arginine levels,the levels of IL-1β,IL-6 and the expression levels of MAPKp38 and MyD88 in the intestine increased first and then decreased(P<0.05).Among them,the lowest level of IL-1β and expression levels of MAPKp38 and MyD88 were observed in Arg2.44 group,and the lowest IL-6 level appeared in Arg2.04 group.The intestinal TNF-α level decreased with the increase of dietary arginine level,and remained stable when the dietary arginine level exceeded 2.04%.The levels of intestinal IL-4 and IL-10 increased first and then decreased with the increase of dietary arginine level,and both reached the maximum value in Arg2.44 group.Intestinal NF-κB level and TLR4 expression level were not significantly affected by dietary arginine levels(P>0.05).The above results indicated that suitable arginine protect mucosal barrier of seabass from damage and alleviate the damage of the mucosal barrier caused by high temperature stress.(3)Effect of dietary arginine on immunity of L.maculatus reared at different water temperaturesThe dietary arginine level and water temperature significantly affected the serum lactic acid(LD)level and lysozyme(LZM)activity of the spotted seabass,and there was a significant interaction(P<0.05).The serum nitric oxide(NO),complement C3 and C4 level,the inducible nitric oxide synthase(iNOS)and LZM activities in 33℃ were significantly lower than those in 27℃(P<0.05),but the serum total nitric oxide synthase(TNOS)and serum lactic acid(LD)levels were significantly higher than that in 27℃(P<0.05).With the increase of dietary arginine level,the activities of serum TNOS and iNOS increased first and then decreased,and when the dietary arginine level was 2.04%,the activities of serum TNOS and iNOS reached the maximum(P<0.05).Serum LZM activity and complement C3 levels of spotted seabass increased significantly with the increase of dietary arginine level(P<0.05).When dietary arginine level was higher than 2.44%,serum LZM activity decreased significantly(P<0.05),but the complement C3 level did not change significantly(P>0.05).On the contrary,the serum lactic acid(LD)content decreased significantly with the increase of dietary arginine level(P<0.05),and its minimum value appeared in Arg2.98 group.Dietary arginine level had no significant effect on serum NO and complement C4 level(P>0.05).The analysis of liver ornithine level showed that the liver arginase activity of spotted seabass was not affected by water temperature and dietary arginine level(P>0.05).Analysis of the NOS activity in head kidney of spotted seabass showed that the TNOS activity of the head kidney in 33℃ group was significantly lower than that in 27℃ group(P<0.05),while the iNOS activity of the head kidney was significantly higher than that in 27℃ group(P<0.05).With the increase of dietary arginine level,the iNOS activity of the head kidney first increased and then decreased(P<0.05),and the maximum value was obtained when the arginine level was 2.44%.Dietary arginine level had no significant effect on head kidney TNOS activity(P>0.05).The above results indicated that the appropriate level of arginine enhance the immunity of spotted seabass and alleviate the immune suppression caused by high temperature stress. |
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