| An 8-week growth trial was conducted to investigate the effects of replacing fish oil(FO)with soybean oil(SO)or palm oil(PO)in diets on growth performance,fatty acid composition and fat metabolism of Groupe.Using fishmeal,soybean meal,casein and gelatin as protein source,fish oil,soybean oil or palm oil as oil source,nine iso-nitrogenous and iso-lipidic diets were formulated to contain different replacement levels of FO with SO or PO.The SO or PO were incrementally added to the basal diet to replace FO by 0,25,50,75 and 100% in the basal diets.A total of 810 healthy fish(mean body weight of 12.59 g)were randomly distributed into27 floating net cage.Triplicate tanks of 30 fish in each cage were fed tested diets to apparent satiation twice daily(6:00 and 18:00)under a natural light regime during a feeding period.The main results shown as following:1.Growth performance and body composition: With the increase in the replacement level of fish oil with SO or PO,the weight gain rate(WGR),and muscle and liver protein contents had a trend of increased and then decreased.The lipid content in liver gradually increased.The lipid content in whole-body and muscle protein contents in palm oil group were higher than those in soybean oil group(P<0.05).The liver lipid content in 75 SO,100SO and 100 PO groups was significantly higher than that in the control group(P<0.05).The growth performance was not affected by plant oil source.The whole-body lipid content and muscle protein content were affected by oil source.Quadratic curve analysis on weight gain against plant oil replacement indicated that the optimal replacing level for SO and PO was 32.9% and 47.4%,respectively.The above results indicated that the replacing of fish oil by soybean oil or palm oil increased the lipld content of the liver.The fat deposition of the palm oil groups were higher than that of the soybean oil groups,and the proportion of palm oil instead of fish oil was higher than that of soybean oil.2.Plasma biochemical indexes,liver oxidation and fat metabolism activity: With the increase in the replacement level of fish oil with SO or PO,the content of T-CHO and HLD-C in plasma showed a trend of increased and then decreased,the CAT activity and MDA content in liver decreased gradually,the LPL and TL in liver decreased and then increased.The plasma HLD-C andGSH-Px activity and MDA content in the control group and 25 SO group were significantly higher than those in 100 SO group(P <0.05).and the HL activity in the controlgroup was significantly lower than that in the 100 SO group(P<0.05).However,the activity of ACC and HSL in 50 SO group were significantly lower than 100SO(P<0.05).The plasma T-CHO and TG content in 50 PO group were significantly higher than those in the 100 PO group(P<0.05),and the TL activity in 50 PO group was significantly lower than that in 75 PO and100PO groups(P<0.05).The plasma CAT activity and MDA content in the 100 PO group were significantly lower than those in the control group(P<0.05).The liver metabolic enzyme activity was not affected by plant oil source.The plasma TG content and liver CAT activity and MDA content were affected by oil source.The above results indicated that 25 SO and 50 PO can relatively improve the fat metabolism of fish,and the antioxidant capacity and lipolytic enzyme activity of the 100 SO and 100 PO groups decreased,and the fatty acid synthase activity increased.3.Fatty acid composition and liver tissue morphology: With the increase in the replacement level of fish oil with SO or PO,the content of C18:1n-9,C18:2n-6(LA)in muscle and liver gradually increased,while C20:4n-6(ARA),C22:6n-3(DHA)and C20:5n-3(EPA)showed an inverse tendency with C18:1n-9 and LA.The muscle C18:1n-9 content in 50SO-100 SO groups were significantly lower than that in the control group(P<0.05),and the muscle ARA content in50PO-100 PO groups were significantly lower than that in the control group(P<0.05).The liver C18:1n-9 content in 75 PO and 100 PO groups were significantly higher than that in the control group(P<0.05).The liver LA in 50SO-100 SO and 100 PO groups were significantly higher than that in the control group(P<0.05).DHA was significantly lower from 50 SO and 50 PO than the control group(P<0.05).The content of C18:1n-9,LA,ARA,EPA,DHA in muscle and C18:1n-9,LA in liver were affected by oil source.In the liver tissue structure,compared with the control group,the 100S0 and 100 PO groups showed nuclear shift or disappearance,fat droplets increased significantly,and cell vacuolation increased significantly.The above results indicate that the replacing of fish oil by soybean oil or palm oil reduces the content of DHA and EPA in liver and muscle,and the fatty acid content of feed has different effects on fatty acids in different tissues of fish.4.Relative mRNA expression of hepatic metabolism: With the increase in the replacement level of fish oil with SO or PO,the expression of FAS,ACC,G6 PD,PPAR?,LPL,?6fad and SREBP-1c genes gradually increased,the expression of ATGL,FABP and HSL genes gradually reduced,the expression of CPT-1,Elov15 and Elovl4 genes increased and decreased,while there was no significant difference in SCD gene expression.The expression of FAS,ACC,G6 PD and LPL genes in 100 SO group and FAS,ACC,G6 PD,HSL,PPAR?,LPL,?6fad and SREBP-1c in 100 PO group were significantly higher than control group(P<0.05),However,the expression of ATGL in 100 SO group and FABP,Elovl5 and ATGL in 100 PO group were significantly lowerthan control group(P<0.05),while the expression of Elovl5 and SREBP-1c in 25 SO group and Elovl4 gene in fish fed 25 PO diet were significantly higher than control group(P<0.05).Except for SCD,all the above genes were affected by plant oil.The above results indicated that the up-regulated expression of genes related to lipogenesis and down-regulated the expression of genes involved in lipolysis in 100 SO and 100 PO groups.The above research results show that a large proportion or even complete replacement of FO in SO or PO will not have a significant impact on the growth of the grouper,but reduce the body health,antioxidant capacity,lipolytic enzyme activity and the content of DHA and EPA in liver and muscle,increase liver fat deposition and cause corresponding damage to its tissue structure. |
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