渔业科学进展  2019, Vol. 40 Issue (4): 21-30  DOI: 10.19663/j.issn2095-9869.20180529003
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引用本文 

胡冬雪, 马季, 王成强, 乔洪金, 王际英, 李宝山, 孙永智. 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼生长性能、体组成和血清生化指标的影响[J]. 渔业科学进展, 2019, 40(4): 21-30. DOI: 10.19663/j.issn2095-9869.20180529003.
HU Dongxue, MA Ji, WANG Chengqiang, QIAO Hongjin, WANG Jiying, LI Baoshan, SUN Yongzhi. Effects of Replacement of Dietary Fish Meal by Nannochloropsis sp. Meal on Growth Performance, Body Composition, and Serum Biochemical Indices of Juvenile Turbot (Scophthalmus maximus L.)[J]. Progress in Fishery Sciences, 2019, 40(4): 21-30. DOI: 10.19663/j.issn2095-9869.20180529003.

基金项目

烟台市重点研发计划(2017ZH066)、山东省自然科学基金青年基金(ZR2017QD007)、海洋公益性行业科研专项(201505022-5)和山东省现代农业产业技术体系藻类产业创新团队项目(SDAIT-26-05)共同资助

作者简介

胡冬雪,E-mail: 1018865124@qq.com

通讯作者

乔洪金,副研究员,E-mail: hongjinqiao@hotmail.com

文章历史

收稿日期:2018-05-29
收修改稿日期:2018-06-25
拟微绿球藻粉替代鱼粉对大菱鲆幼鱼生长性能、体组成和血清生化指标的影响
胡冬雪 1,2, 马季 1,2, 王成强 2, 乔洪金 2, 王际英 2, 李宝山 2, 孙永智 2     
1. 上海海洋大学水产科学国家级实验教学示范中心 农业农村部鱼类营养与环境生态研究中心 水产动物遗传育种中心上海市协同创新中心 上海 201306;
2. 山东省海洋资源与环境研究院 山东省海洋生态修复重点实验室 烟台 264006
摘要:为探讨拟微绿球藻(Nannochloropsis sp.)粉替代鱼粉对大菱鲆(Scophthalmus maximus L.)幼鱼生长性能、体组成和血清生化指标的影响,用拟微绿球藻粉替代基础饲料中0%、3.88%、7.76%、11.64%和15.52%的鱼粉,配制成5种等氮等能的饲料(N0、N3.88、N7.76、N11.64、N15.52)。选取初始体重为(24.60 ±0.02) g的大菱鲆幼鱼600尾,随机分成5组,每组3个重复,每个重复40尾鱼,养殖周期70 d。结果显示:1)各实验组大菱鲆幼鱼的增重率(WGR)、特定生长率(SGR)、蛋白质效率(PER)、饲料系数(FCR)、日摄食率(DFI)、肥满度(CF)和成活率(SR)均无显著差异(P>0.05);2)随着藻粉添加量的增加,全鱼及肌肉中粗脂肪含量显著降低(P < 0.05),粗蛋白、粗灰分和水分含量无显著差异(P>0.05);3)血清溶菌酶(LZM)、补体蛋白C3、补体蛋白C4及酸性磷酸酶(ACP)活力均呈先上升后下降的趋势,分别在N7.76、N7.76、N11.64、N7.76组达到最大值,且显著高于N0组(P < 0.05),N15.52组碱性磷酸酶(ALP)显著低于其他组(P < 0.05),其他组之间无显著差异(P>0.05);4)藻粉组血清总超氧化物歧化酶(T-SOD)、总抗氧化能力(T-AOC)和谷胱甘肽过氧化物酶(GSH-PX)活力,均呈先上升后下降的趋势,在N7.76组达到最大值,且显著高于N0组(P < 0.05);5) N7.76组血清甘油三酯(TG)含量显著低于其他组(P < 0.05),其他组之间无显著差异(P>0.05),藻粉组血清总胆固醇(TCHO)显著低于N0组(P < 0.05),各藻粉组之间差异不显著(P>0.05);6)藻粉组血清谷草转氨酶(AST)活力呈先下降后上升的趋势,N11.64组达到最小值,显著低于N0组(P < 0.05),藻粉组谷丙转氨酶(ALT)活力显著低于N0组(P < 0.05)。研究表明,本实验条件下,拟微绿球藻粉替代大菱鲆幼鱼饲料中15.52%的鱼粉对其生长无显著影响,替代7.76%可显著提高其非特异性免疫力,降低血脂水平。
关键词大菱鲆    拟微绿球藻粉    生长    抗氧化能力    
Effects of Replacement of Dietary Fish Meal by Nannochloropsis sp. Meal on Growth Performance, Body Composition, and Serum Biochemical Indices of Juvenile Turbot (Scophthalmus maximus L.)
HU Dongxue 1,2, MA Ji 1,2, WANG Chengqiang 2, QIAO Hongjin 2, WANG Jiying 2, LI Baoshan 2, SUN Yongzhi 2     
1. National Demonstration Center for Experimental Fisheries Science Education, Centre for Research on Environmental Ecology and Fish Nutrion (CREEFN) of the Ministry of Agriculture and Rural Affairs, Shanghai Collaborative Innovation for Aquatic Animal Genetics and Breeding, Shanghai Ocean University, Shanghai 201306;
2. Shandong Marine Resource and Environment Research Institute, Shandong Provincial Key Laboratory of Restoration for Marine Ecology, Yantai 264006
Abstract: A 70-day trial was conducted to investigate the effect of replacement of dietary fish meal by Nannochloropsis sp. meal on growth performance, body composition, and serum biochemical indices of juvenile turbot Scophthalmus maximus L. with an initial weight body weight of (24.60±0.02) g. Five isonitrogenous and isoenergetic diets (N0, N3.88, N7.76, N11.64, and N15.52) were formulated with 0%, 3.88%, 7.76%, 11.64%, and 15.52% fish meal replaced by Nannochloropsis sp. meal, respectively. Each diet was randomly fed to three replicates of fish, with 40 fish per replicate. The following results were obtained. 1) There were no significant differences (P>0.05) in weight growth rate, specific growth rate, protein efficiency ratio, feed coefficient ratio, feed intake, condition factor, and survival rate among the groups. 2) As the meal content of Nannochloropsis sp. increased, the crude lipid content in the whole body and muscle was significantly decreased (P < 0.05); however the crude protein, crude ash, and moisture content were not significantly different (P>0.05). 3) Lysozyme, complement protein C3, complement protein C4, and acid phosphatase activities showed a rising trend followed by a decline, with the highest point reached in the N7.76, N7.76, N11.64, and N7.76 groups, respectively, and were significantly higher than that in the N0 group (P < 0.05). The alkaline phosphatase activity of the N15.52 group was significantly lower than that the other groups and there were no significant differences among other groups (P>0.05). 4) The total superoxide dismutase, total antioxidant capacity, and glutathione peroxidase activities in the serum of the algae meal groups first increased and then decreased, and reached a maximum in the N7.76 group, which was significantly higher than that in the N0 group (P < 0.05). 5) The triglyceride content in the serum of the N7.76 group was significantly lower than that in the other groups (P < 0.05), and there were no significant differences among the other groups (P>0.05). The total cholesterol content of the algae meal groups was significantly lower than in the N0 group (P < 0.05), but there were no significantly differences among the algae meal groups. 6) The aspartate aminotransferase activity in the serum of the algae meal groups followed a decreasing to increasing trend, reaching the lowest point in the N11.64 group and was significantly lower than that in the N0 group (P < 0.05). The alanine aminotransferase activity of the algae meal groups was significantly lower than that in the N0 group (P < 0.05). In conclusion, under the experimental conditions tested, Nannochloropsis sp. meal could replace 15.52% of fish meal in juvenile turbot feed without any effects on the growth performance, and the replacement of 7.76% fish meal significantly improved the nonspecific immunity and reduced the blood lipid levels in juvenile turbot.
Key words: Juvenile turbot    Nannochloropsis sp. meal    Growth performance    Antioxidant activity    

大菱鲆(Scophthalmus maximus)隶属于菱鲆科(Scophthal midae),瘤棘鲆属(Psettamaxima),它的肌肉丰厚白嫩、骨刺少、内脏团小、出肉率高,口感爽滑甘美,是我国北方主要的海水养殖品种之一,也是世界公认的优质比目鱼类之一。鱼粉是名贵水产鱼类配合饲料中的主要蛋白质来源,但近年来远洋捕获的鲜杂鱼已经达到或者接近最大可持续生产(Rana et al, 2009; Krisetherton et al, 2009),造成了鱼粉供需之间的矛盾。寻找新型蛋白原料(Olsen et al, 2012),替代或减少鱼粉的使用成了目前水生动物营养研究的重点方向之一。

植物蛋白存在抗营养因子和氨基酸的平衡问题(Thompson et al, 2012),在大菱鲆配合饲料中的使用比例较低。研究表明,大豆浓缩蛋白仅能替代17%的鱼粉而对大菱鲆幼鱼的生长不产生影响(Day et al, 2015);玉米蛋白替代大菱鲆幼鱼饲料中21%的鱼粉对其生长性能和饲料效率无显著差异(Regost et al, 1999);复合植物蛋白替代20.7%的鱼粉显著降低大菱鲆幼鱼的生长性能(陈超, 2012)。微藻,如拟微绿球藻(Nannochloropsis sp.)、小球藻(Chlorela)及螺旋藻(Spirulina),含有人体所需的20种氨基酸、多种维生素和微量元素,以及亚油酸和亚麻酸等高度不饱和脂肪酸(Yamaguchi, 1996; Emma et al, 2017),是替代鱼粉蛋白的理想原料。对鲫鱼(Carassius auratus) (石西, 2015)、罗非鱼(Oreochromis spp) (Olvera-Novoa et al, 1998)和虹鳟(Oncorhynchus mykiss) (Dallaire, 2007)的研究表明,微藻粉替代适量的鱼粉对其生长无抑制作用。此外,郭斌等(2018)研究表明,10%的藻渣与51%复合植物蛋白粉替代35%的鱼粉,不影响大菱鲆的生长性能,且能促进摄食率、降低饲料系数,而10%的浒苔与51%复合植物蛋白粉替代35%的鱼粉显著降低大菱鲆生长性能。

拟微绿球藻是海洋单细胞微藻,属于褐藻门(Ochrophyta),真眼点纲(Eustig¬matophyceae),适温范围广,易于培养,繁殖快,含有丰富的天然色素如玉米黄素和虾青素,可以增强免疫能力和抗氧化能力(吴吉林等, 2010),且含有丰富的高不饱和脂肪酸,尤其是EPA(余颖等, 2005),可以提高鱼虾蟹苗种的发育和存活率(杜涛等, 2010; Marques et al, 2006)。目前,尚无关于微藻粉替代大菱鲆配合饲料中鱼粉的相关报道,因此,本研究旨在探索拟微绿球藻粉替代鱼粉对大菱鲆幼鱼生长、体组成、非特异性免疫和血清生化指标的影响,为微藻粉在水产配合饲料中的应用提供参考。

1 材料与方法 1.1 实验设计

以鱼油和玉米油为主要脂肪源,用拟微绿球藻藻粉分别替代基础饲料中0、3.88%、7.76%、11.64%和15.52%的鱼粉,制成5种等氮等能的实验饲料(N0、N3.88、N7.76、N11.64、N15.52),N0为对照组。在各替代组中分别添加晶体蛋氨酸、赖氨酸和精氨酸,保持各饲料中必需氨基酸的平衡。饲料配方及营养组成见表 1

表 1 饲料配方及营养组成(%干物质) Tab.1 Composition and nutrient levels of the experimental diets (% dry mater)
1.2 实验管理及样品采集

实验鱼购自蓬莱宗哲养殖有限公司,养殖实验在山东省海洋资源与环境研究院养殖实验室进行。正式实验前,实验鱼在养殖系统中驯养14 d,期间投喂对照组饲料。实验鱼禁食24 h,挑选初始体重为(24.60± 0.02) g的600尾大菱鲆幼鱼,随机分5组,每组设3个重复,每个重复40尾鱼,每天定时定量投喂2次(08:00和15:30),投喂量为鱼体重的1%~2%,根据摄食情况调整投喂量,投喂结束0.5 h左右排残饵,数颗粒,计算残饵量。养殖环境:绿色圆柱形水桶(直径80 cm,高70 cm,水深为50 cm),水温为(17.32±0.20)℃,pH为7.8~8.2,盐度为28~30,溶氧>5 mg/L,氨氮、亚硝酸氮均<0.1 mg/L。

70 d养殖实验结束后,禁食24 h,记录每桶鱼的存活数量并称重,计算存活率和增重率。随机取3尾用于全鱼常规分析,剩余随机取15尾测量体长、体重,计算肥满度,尾静脉取血后,分离内脏和背肌,并分别称重,计算脏体比。背肌-20℃保存,用于常规分析,以上取样均在冰盒上进行。血样在4℃冰箱静置4 h,离心分离(4000 r/min, 10 min),取上清液,-80℃保存,用于测定血清生理生化指标。

1.3 测定指标和样品分析方法

     增重率(WGR, %)=(Wt - W0)/W0×100

特定生长率(SGR, % /d)=(ln Wt - ln W0)/d×100;

  蛋白质效率(PER, %)=(Wt-W0)/(F×P)×100;

    饲料系数(FCR) = F/(Wt-W0);

日摄食率(DFI, %/d) = F/[(W0 + Wt)/2×d] ×100;

    脏体比(VSI, %) =Wv / Wt×100;

     肥满度(CF) = Wt / L3×100;

    成活率(SR, %) = Nt / N0×100;

式中,Wt为实验鱼末体重(g),W0为实验鱼初体重(g),d为养殖天数,F为摄食干饲料重(g),P为饲料中粗蛋白质的含量(%),Wv为内脏质量,L为实验末鱼体长,Nt为实验末鱼的数量,N0为实验初鱼的数量。

饲料及组织样品分析方法,水分测定采用105℃烘干恒重法测定(GB/T6435- 2006);粗蛋白测定采用凯氏定氮法(GB/T6432- 2006);粗脂肪采用索氏抽提法测定(GB/T6433- 2006);粗灰分测定采用马弗炉550℃灼烧法(GB/T 6438-2007)。

血清溶菌酶(LZM)、总抗氧化能力(T-AOC)、总超氧化物歧化酶(T-SOD)、谷胱甘肽过氧化物酶(GSH-PX)活力及丙二醛(MDA)含量采用南京建成的试剂盒测定;补体蛋白C3和补体蛋白C4采用江莱生物酶联免疫分析(ELISA)试剂盒测定。

血清甘油三酯(TG)、胆固醇(CHO)、低密度脂蛋白胆固醇(LDL-C)、高密度脂蛋白胆固醇(HDL-C)、碱性磷酸酶(ALP)、酸性磷酸酶(ACP)、谷草转氨酶(AST)、谷丙转氨酶(ALT)、采用全自动生化分析仪(7020, 日立, 日本)进行测定,试剂盒均购自四川迈克生化技术有限公司。

1.4 数据统计分析

采用SPSS18.0软件对数据进行单因素方差分析(One-Way ANOVA),当处理之间差异显著(P < 0.05)时,用Duncan’s检验进行多重比较,结果以平均值±标准差(Means±SD)形式表示。

2 结果 2.1 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼生长及饲料利用的影响

拟微绿球藻粉替代鱼粉对大菱鲆幼鱼生长和饲料利用数据见表 2。随着拟微绿球藻粉替代比例增大,大菱鲆幼鱼WGR、SGR、PER和CF呈逐渐上升的趋势,但各组间无显著差异(P>0.05),FCR和DFI呈逐渐下降的趋势,无显著差异(P>0.05);藻粉替代鱼粉对实验鱼的VSI和SR均无显著影响(P>0.05)。

表 2 微藻粉替代鱼粉对大菱鲆幼鱼生长性能及饲料利用的影响(n=3; x±SD) Tab.2 Effects of fish meal replacement by microalgae meals on growth performance and feed utilization of juvenile turbot
2.2 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼全鱼和肌肉体组成的影响

表 3所示,藻粉组的全鱼和肌肉粗脂肪含量呈逐渐下降的趋势,显著低于N0组(P < 0.05);藻粉替代鱼粉对全鱼和肌肉的水分、粗蛋白及粗灰分的含量均无显著影响(P>0.05)。

表 3 微藻粉替代鱼粉对大菱鲆幼鱼体组成的的影响(%湿重; n=3; x±SD) Tab.3 Effects of fish meal replacement by microalgae meals on tissue proximate composition of juvenile turbot (%wet weight; n=3; x±SD)
2.3 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼血清非特异性免疫的影响

表 4所示,LZM和补体蛋白C3活力呈先上升后下降的趋势,在N7.76组达到最大值并显著高于N0组(P < 0.05);补体蛋白C4活力呈先上升后下降的趋势,在N11.64组达到最大值并显著高于N0组(P < 0.05);ACP活力呈先上升后下降趋势,N7.76组达到最大值,并显著高于N0组(P < 0.05)。

表 4 微藻粉替代鱼粉对大菱鲆幼鱼血清非特性免疫能力的影响(n=3; x±SD) Tab.4 Effects of fish meal replacement by microalgae meals on serum non-specific immune index of juvenile turbot (n=3; x±SD)
2.4 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼抗氧化能力的影响

表 5所示,随着拟微绿球藻粉的替代量增大,T-SOD、T-AOC和GSH-PX活力呈先上升后下降的趋势,在N7.76组达到最大值并显著高于N0组(P < 0.05),而MDA含量呈逐渐下降的趋势并显著低于N0组(P < 0.05)。

表 5 微藻粉替代鱼粉对大菱鲆幼鱼血清抗氧化能力的影响(%湿重; n=3; x±SD) Tab.5 Effects of fish meal replacement by microalgae meals on serum antioxidant indeices of juvenile turbot (%wet weight; n=3; x±SD)
2.5 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼血清血脂指标的影响

表 6所示,血清TG呈先下降后上升的趋势,在N7.76组达到最低值并且显著低于N0组(P < 0.05);藻粉组血清TCHO含量显著低于N0组(P < 0.05),但各藻粉组之间无显著差异(P < 0.05);LDL-C含量呈下降趋势,HDL-C含量呈先上升后下降的趋势,在N7.76组达到最大值并显著高于N0组(P < 0.05),且N11.64和N15.52组显著低于N0组(P < 0.05);藻粉组血清LDL-C/ HDL-C显著低于N0组(P < 0.05),但各藻粉组之间无显著差异(P>0.05)。

表 6 微藻粉替代鱼粉对大菱鲆幼鱼血清血脂指标的影响(n=3; x±SD) Tab.6 Effects of fish meal replacement by microalgae meals on serum lipid of juvenile turbot (n=3; x±SD)
2.6 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼血清代谢指标的影响

表 7所示,AST呈先下降后上升的趋势,N11.64组达到最小值,显著低于N0组(P < 0.05),而ALT呈逐渐下降趋势,显著低于N0组(P < 0.05)。

表 7 微藻粉替代鱼粉对大菱鲆幼鱼血清代谢指标的影响(n=3; x±SD) Tab.7 Effects of fish meal replacement by microalgae meals on serum metabolic index of juvenile turbot (n=3; x±SD)
3 讨论 3.1 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼生长及饲料利用的影响

研究表明,饲料中添加适量的海藻(2.5%~10%)可提高鱼类生长、饲料利用和抗病力(Norambuena et al, 2015; Wassef et al, 2005)。本研究中,拟微绿球藻粉替代鱼粉对大菱鲆幼鱼的生长和饲料的利用均无显著影响,大菱鲆幼鱼的成活率(SR)介于97.5%~100%,各组无显著差异。微藻组与鱼粉组SR相比没有显著降低,这与各组之间成活率均较高有关。大菱鲆幼鱼增重率(WGR)、特定生长率(SGR)和肥满度(CF)均无显著差异,与郭斌等(2018)实验结果一致,而日摄食率(DFI)与其研究结果不同,DFI可能与其含有的诱食作用的物质含量有关,例如,海藻中常见的二甲基-β-丙酸噻亭(DMPT) (邹仕庚等, 2005),可以增加摄食率,因本研究中未对拟微绿球藻的诱食成分进行测定,其与微藻渣的差异需进一步研究。与鱼粉组相比,大菱鲆幼鱼饲料系数(FCR)无显著差异,这与小球藻粉替代鲫鱼饲料中鱼粉的报道存在差异(石西等, 2015)。随着小球藻替代鲫鱼饲料中鱼粉比例增加,饲料系数呈先下降后升高的趋势,出现差异的原因可能是小球藻粉最低替代水平21.8%远高于本研究拟微绿球藻粉最高替代水平15.52%,拟微绿球藻粉的添加量可能尚未到达引起饲料系数升高的拐点。与鱼粉组相比,藻粉组大菱鲆幼鱼脏体比(VSI)无显著差异,这与曹申平等(2016)螺旋藻对异育银鲫幼鱼的研究和Miller等(2007)对大西洋鲑鱼(Salmost salar)的研究相符,而与石西等(2015)小球藻在鲫鱼幼鱼中的研究结果不一致,其原因可能与鱼的初末体重有关,也可能与选用的是藻粉种类或替代量有关。

3.2 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼全鱼和肌肉体组成的影响

研究表明,微藻替代鱼粉对鱼体组成产生一定影响,但这些影响对鱼的营养价值影响比较小(Tibaldi et al, 2015; Kissinger et al, 2016)。本研究中,大菱鲆幼鱼全鱼的水分、粗蛋白和粗灰分不受拟微绿球藻粉添加量的影响,这与郭斌等(2018)慈丽宁(2011)张燕等(2017)研究结果一致,说明添加适量的拟微绿球藻粉替代大菱鲆幼鱼饲料中鱼粉对其全鱼和肌肉蛋白质含量无显著影响。而大菱鲆全鱼和肌肉粗脂肪含量呈下降趋势,这可能与拟微绿球藻粉中含有较多的EPA有关,EPA可以抑制6-磷酸葡萄糖脱氢酶、乙酰羟化酶和苹果酸脱氢酶的活性,使肝脏内脂肪合成能力减弱,从而影响脂肪的合成(胡斌等, 2013)。此外,微藻粉含有较多的色素类成分和纤维素(Iα型)等非淀粉性多糖,不能被鱼类充分吸收利用(Lubian et al, 2002),从而影响脂肪的沉积,这一研究结果与星斑川鲽(Platichthys stellatus)幼鱼饲料中添加拟微绿球藻粉的实验结果一致(张燕等, 2017)。

3.3 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼血清非特异性免疫指标的影响

溶菌酶(LZM)通过溶解细菌的细胞壁来完成免疫反应,是鱼类非特异性免疫系统的重要组成部分。本研究中,藻粉组血清中LZM活力呈先上升后下降的趋势,在N7.76组达到最大值并显著高于对照组,这说明适量的拟微绿球藻粉可以提升鱼类溶菌酶免疫功能,而过量的会对鱼类溶菌酶免疫产生抑制作用。补体蛋白C3和补体蛋白C4是鱼类血清和组织液中一组经活化后具有酶活性的蛋白质,补体蛋白C3主要是由巨噬细胞、淋巴组织和骨髓等合成的β球蛋白,可以在补体蛋白C3裂解酶的作用下参与补体激活,补体蛋白C4也是补体经典激活途径的重要组分(慈丽宁, 2011)。本研究补体蛋白C3活力呈先上升后下降趋势,在N7.76组达到最大值并显著高于对照组,而补体蛋白C4活力呈先上升后下降的趋势,在N11.64组达到最大值并显著高于对照组,原因是拟微绿球藻含有的藻多糖(PSP)可以与补体因子结合激活免疫系统,促进细胞的吞噬活性(Dalmo et al, 1996),这表明适量的拟微绿球藻粉可以提高大菱鲆幼鱼非特异性免疫能力。ALP和ACP是鱼类非特性免疫的重要指标,对鱼体抗病力和抗应激力起促进作用。本研究中,血清中ALP含量仅N15.52组显著低于对照组,ACP先上升后下降,在N7.76组达到最大值并显著高于对照组。可能是拟微绿球藻中多糖和寡糖起到激活非特异性免疫的作用。

3.4 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼抗氧化指标的影响

总超氧化物歧化酶(T-SOD)、总抗氧化能力(T-AOC)和谷胱甘肽过氧化物酶(GSH-PX)等活性在一定程度上能够反映机体抵抗氧化应激的能力,当机体发生氧化损伤时,脂质过氧化物水平往往升高,抗氧化能力下降(梅琳等, 2015)。本研究中,随着拟微绿球藻粉的替代比例增大,血清中T-SOD、T-AOC和GSH-PX活力呈先上升后下降的趋势,均在N7.76组达到最大值,并显著高于对照组。说明拟微绿球藻粉替代鱼粉的水平为7.76%时,大菱鲆的抗氧化能力达到最大值。随着替代量的增加,对机体可能存在损伤,说明适量的拟微绿球藻粉的添加有利于大菱鲆幼鱼抗氧化能力的提高,过多不利于大菱鲆幼鱼的生长。丙二醛(MDA)是膜脂过氧化作用的最终分解产物,其含量可以反映大菱鲆幼鱼遭受胁迫伤害的程度(Martínez-Álvarez et al, 2005; Jain et al, 2001),藻粉组血清中MDA含量呈逐渐下降的趋势,并显著低于对照组,说明适量的拟微绿球藻粉的添加有利于大菱鲆幼鱼的抗胁迫能力。

3.5 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼血脂指标的影响

本研究中,拟微绿球藻粉的添加显著影响大菱鲆幼鱼的血脂水平。随着拟微绿球藻粉替代比例增加,藻粉组TCHO呈逐渐下降趋势,而TG呈先下降后上升的趋势,在N7.76组显著低于对照组,造成血脂水平降低的原因可能是拟微绿球藻粉含有大量的高不饱和脂肪酸和类胡萝卜素,特别是EPA含量占总脂肪含量的35% (魏东等, 2000),具有抗血栓和调节血脂的作用,其次含有较多亚油酸和亚麻酸,这2种高不饱和脂肪酸是线粒体膜磷脂和细胞膜重要组成成分,可以减少胆固醇和甘油三酯在肝脏和脂肪中的沉淀和堆积(Werman et al, 2003),有降脂的作用(Abdel et al, 2009)。血清中LDL-C含量增加可以使更多的TCHO和TG转运到血液,而HDL-C可以使更多的TCHO转运到肝脏,LDL-C和HDL-C影响血清中的TCHO和TG的含量(曹林等, 2017)。本研究中LDL-C呈下降趋势,HDL-C呈先上升后下降趋势,LDL-C/ HDL-C显著低于对照组,各藻粉组间无显著差异。说明饲料中添加适量拟微绿球藻对降低低密度脂蛋白含量,增加高密度脂蛋白含量有一定作用,同时能显著降低密度脂蛋白与高密度脂蛋白的比值,有利于大菱鲆的血脂健康。

3.6 拟微绿球藻粉替代鱼粉对大菱鲆幼鱼血清代谢指标的影响

谷草转氨酶(AST)和谷丙转氨酶(ALT)是反映肝功能的指标,AST主要存在肝细胞线粒体内,当肝脏发生严重坏死和破损时,才会导致血清中AST偏高(魏佳丽等, 2016)。本研究中,AST呈先下降后上升的趋势,原因是拟微绿球藻粉含有亚油酸和亚麻酸,可以防止胆固醇和甘油三脂在肝脏中的堆积,一定替代范围内可以保护肝脏等组织的正常生理功能不受损伤,但随着添加量的增加,这种保护作用会呈下降趋势甚至过多的添加可能造成损伤。ALT主要存在于肝细胞中,血清中含量很低,只有当细胞大量坏死或者细胞膜的通透性增强时含量会增加(Chen et al, 2003)。本实验中ALT呈下降趋势,说明添加一定量的拟微绿球藻粉可能维持了肝细胞膜对ALT的稳定性。

4 结论

综上所述,在本实验条件下,用拟微绿球藻粉替代15.52%以内鱼粉对大菱鲆幼鱼的生长性能无显著影响,同时可以降低脂肪在鱼体内的沉积;添加7.76%的拟微绿球藻粉替代鱼粉能够显著提高大菱鲆幼鱼的免疫性能和抗氧化能力,同时保护其营养价值。

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