| This study investigated the effects of different dietary levels of ARA and DHA/EPA ratios on the synthesis of gonadal steroid hormones in tongue sole broodstock and the effects of different levels of dietary DHA/EPA on the growth performance,fatty acid composition and related gene expression in tongue sole juvenile(Cynoglossus semilaevis).The experiment was conducted in an indoor seawater system.The temperature range of the experiment was 20 ~ 26?;salinity,30 ~ 31;pH,7.4 ~ 8.5;dissolved oxygen,5 ~ 7 mg L-1;light intensity,100 ~ 500 lx.The results showed that:1.Three isonitrogenous and isolipidic experimental diets were formulated to contain different ARA levels: the control diet without ARA supplementation(C,0.58% ARA of total fatty acids(TFA))and two diets with low(5.14% of TFA,ARA-L)or high ARA(15.44% of TFA,ARA-H)supplementation.The feeding trial was conducted in an indoor seawater system for a period of 3 months.Results showed that ARA supplementation significantly reduced the estradiol production in females(P<0.05),but stimulated the testosterone production in males(P<0.05).ARA supplementation significantly reduced the mRNA expression of aromatasein ovaries(P<0.05)but significantly increased the gene expression of 3?-hydroxysteroid dehydrogenase(3?-HSD)in testes(P<0.05).In mature ovaries,diet ARA-L significantly reduced the gene expression of follicle stimulating hormone receptor(FSHR),3?-HSD and 17?-HSD(P<0.05);however,in immature ovaries,it significantly increased the gene expression of FSHR,steroidogenic acute regulatory protein(StAR),cholesterol side-chain cleavage enzyme(P450ssc),3?-HSD and 17?-HSD(P<0.05).In all gonads,17-hydroxylase(P450c17)responded to dietary ARA differently from other sex steroid-synthesizing proteins.ARA was preferentially accumulated in tongue sole gonad lipids.ARA concentrations were highest in gonad,liver and muscle lipids of MM fish and lowest in MF fish.Compared to female tongue sole,males had higher DHA concentrations in gonad lipids,but lower concentrations in liver lipids.In conclusion,results suggest dietary ARA regulates sex steroid hormone synthesis in tongue sole broodstock,and accumulate singonad lipids,depending on both fish gender and maturation stage.Dietary ARA supplementation appears more important for male fish than for female fish,and more important for immature females than for mature females.2.Three isonitrogenous and isolipidic experimental diets were formulated to contain different DHA/EPA levels: group D/E-0.68(with a DHA/EPA ratio of 0.68)?group D/E-1.09(with a DHA/EPA ratio of 1.09)and group D/E-2.05(with a DHA/EPA ratio of 2.05).The feeding trial was conducted in an indoor seawater system for a period of 3 months.Results showed that compared with the group D/E-0.68,group D/E-1.09 significantly increased the estradiol content in serum of female fish(P<0.05),while D/E-2.05 group significantly increased the testosterone content in serum of males(P<0.05).Compared to group D/E-0.68,group D/E-1.09 significantly increased the gene expression of follicle stimulating hormone receptor(FSHR),17–hydroxylase(P450c17),steroidogenic acute regulatory protein(StAR)and 3?-hydroxysteroid dehydrogenase(3?-HSD)in ovaries(P<0.05).In the testis,compared with group D/E-0.68,groups D/E-1.09 and D/E-2.05 increased the gene expression of FSHR,cholesterol side-chain cleavage enzyme(P450ssc)and 3?-HSD(P<0.05).The DHA/EPA ratios in fish tissue increased with the increase of dietary DHA/EPA ratios,but DHA contents in all fish tissues were significantly higher than EPA.The content of DHA in male gonads was significantly higher than that in females,indicating that males may requires higher DHA than females.In conclusion,the results showed that the dietary DHA/EPA ratio regulates the synthesis of gonadal steroid hormone synthesis in the broodstock,and the regulation varied between females and males.The male fish may require a higher dietary DHA/EPA ratio than females for gonadal stetroidogenesis.3.The effects of dietary DHA/EPA ratios on the growth performance,fatty acid composition and related gene expression in tongue sole juvenile(23.40±0.08g)were studied.The isonitrogenous and isoenergetic diets with different DHA/EPA ratios(0.61,1.02,1.46,1.91,2.32 and 2.75)were foumulated and designated as D/E-0.61,D/E-1.02,D/E-1.46,D/E-1.91,D/E-2.32 and D/E-2.75 respectively.The feeding trial was conducted in an indoor seawater system for a period of 80 days.The results showed that the weight gain(WG)increased significantly(P<0.05)with the increase of DHA/EPA ratio from 0.61 to 1.91,and then decreased significantly.WG has a maximum value in groups D/E-1.46 and D/E-1.91.Feed efficiency(FE)has similar trend.However,there was no significant difference in survival(SR),feed intake(FI),hepato somatic index(HSI),viserol somatic index(VSI)and condition factor(CF)between the treatment groups(P>0.05).The lipid content of the fish increased first and then decreased with the increase of DHA/EPA ratio in the diet,and the highest value appeared in groups D/E-1.02 and D/E-1.46(P<0.05).The of fatty acid compositions in fish tissue closely reflected those of diets,and the DHA contents in fish tissues were much higher than those of EPA.The gene expression of PPAR?2(peroxisome proliferator-activated receptor ?2 subtype)and ACO3(acetyl-CoA oxidase 3 subtype)showed an increasing trend with the increase of dietary DHA/EPA ratio(P<0.05).Gene expressions of PPAR?(peroxisome proliferator-activated receptor gamma subtype),SREBP(cholesterol regulatory element binding protein),ACC(acetyl-CoA carboxylase),FAS(fatty acid synthase)and ATGL(adipose triglyceride lipase)increased first and then decreased(P<0.05).The highest value of GPAT4(glycerol-3-phosphate acyltransferase 4 subtype)appeared in groups D/E-1.02 and D/E-1.46(P<0.05).There was no significant difference in gene expressions of PPAR?1(peroxisome proliferator-activated receptor ?1 subtype)and CPT-1?(carnitine palmitoyltransferase 1? subtype)among dietary treatments(P>0.05).In conclusion,the moderate DHA/EPA ratios in diet(1.46-1.91)could significantly enhance the growth of juveniles.With the weight gain as the evaluation index,quadratic curve analysis showed that the optimum DHA/EPA ratio in diets of juvenile tongue sole was 1.67. |
PDF Full Text Request