罗非鱼无乳链球菌LrrG-Sip融合基因原核表达载体的构建及表达

LrrG和表面免疫原性蛋白（Sip）是无乳链球菌（Streptococcus agalactiae）的2种表面蛋白,具有良好的免疫原性。为获得罗非鱼无乳链球菌表面蛋白LrrG和Sip蛋白的融合蛋白,该试验采用基因拼接技术中的双酶切法分2步逐个将Sip和LrrG基因插入pColdⅡ载体中,构建原核表达载体pColdⅡ-LrrG-Sip。将成功构建的融合基因原核表达载体转化感受态细胞BL21（DE3）,进行诱导表达条件的优化。结果显示,15℃、IPTG 0.5 mmol·L-1诱导9 h,目的蛋白呈可溶状态的表达量最高。Western Blot检测结果显示LrrG-Sip融合蛋白大小与预测一致（162kDa）,说明成功构建了融合基因,为罗非鱼源无乳链球菌亚单位疫苗的研制奠定了基础。     

罗非鱼无乳链球菌LrrG蛋白的原核表达及免疫原性分析

LrrG蛋白是无乳链球菌较保守的表面蛋白之一。为获得罗非鱼源无乳链球菌LrrG蛋白并探讨其在罗非鱼体内的免疫原性,本实验根据GenBank中已报道的人源无乳链球菌LrrG基因序列,设计特异性引物,扩增获得罗非鱼源无乳链球菌的LrrG基因。分析表明,其ORF为2 361 bp,编码786个氨基酸,与人源无乳链球菌LrrG基因核苷酸序列的相似性高达98.48%。LrrG蛋白含有3个保守的LRR结构域,并可形成多个抗原表位。将LrrG基因片段克隆转入原核表达载体pET-32a(+),构建重组质粒pET-32a(+)/LrrG,E.coli BL21(DE3)22℃诱导表达6 h。SDS-PAGE显示,诱导表达蛋白的分子量为108.9 ku,并且该重组蛋白以可溶和包涵体2种形式存在。经His Bind亲和柱纯化及超滤管浓缩后,LrrG可溶蛋白浓度达3.40 mg/mL。鱼体注射免疫实验表明,LrrG可溶蛋白对罗非鱼的相对免疫保护率达69.28%,且免疫后4周的血清抗体滴度为1∶800。该研究为深入探讨无乳链球菌LrrG蛋白作为罗非鱼基因工程疫苗的潜在应用价值奠定了基础。     

罗非鱼无乳链球菌Sip-Pgk融合蛋白乳酸菌口服疫苗制备及其免疫效果的研究

为研制比无乳链球菌(Streptococcus agalactiae)单个蛋白抗原免疫效果更佳的多蛋白重组罗非鱼(Oreochromis sp.)链球菌病口服疫苗,该研究利用同源重组法构建表达无乳链球菌Sip-Pgk融合蛋白的pNZ8148-sippgk质粒,通过电转化乳酸乳球菌(Lactococcus lactis) NZ9000中获得L. lactis NZ9000 pNZ8148-sip-pgk重组乳酸菌,使用nisin诱导表达并进行Western blot鉴定,制备Sip-Pgk融合蛋白乳酸菌口服疫苗,通过不同免疫次数隔周免疫的方式灌胃罗非鱼。ELISA检测免疫后的血清抗体水平,在灌胃免疫结束后的第18天通过腹腔注射无乳链球菌攻毒获得相对免疫保护率。结果显示,构建的重组乳酸菌诱导表达的蛋白大小为92 kD,与目的蛋白大小一致。与2次免疫比较,3次免疫该融合蛋白乳酸菌疫苗能显著提高罗非鱼的血清抗体水平和对无乳链球菌的免疫保护效果。3次免疫Sip-Pgk融合蛋白乳酸菌疫苗的血清水平显著高于单一蛋白组和PBS组,其相对免疫保护率最高(45.56%)。     

尼罗罗非鱼无乳链球菌Sip蛋白乳酸菌活载体口服疫苗的研制及其免疫效果

链球菌病是威胁我国罗非鱼养殖产业健康发展的重要病害之一。为研制出免疫效果好、操作简便的罗非鱼链球菌病疫苗,本研究构建重组表达无乳链球菌Sip蛋白的穿梭质粒pNZ8124-Sip,通过酶切和测序验证后电转化乳酸乳球菌NZ9000,获得能够诱导重组表达无乳链球菌Sip蛋白的乳酸菌活菌载体疫苗。采用SPS-PAGE电泳摸索最佳诱导浓度和诱导时间以获得最大表达量,通过镍柱纯化目的蛋白并进行Western blot检测;利用不同浓度的重组乳酸菌活载体疫苗灌胃口服免疫尼罗罗非鱼,采用间接ELISA法测定免疫后血清抗体水平变化,通过人工腹腔注射感染无乳链球菌获得相对免疫保护率。研究结果显示,构建的重组乳酸乳球菌可通过nisin诱导表达大小为48 ku特异性蛋白,与目的蛋白大小一致;PAGE电泳显示,重组蛋白主要以可溶蛋白和包涵体2种形式存在,其中胞内可溶性蛋白浓度达7.65 mg/mL;诱导表达的最佳条件为100 ng/mL nisin诱导6 h;Western blot检测结果显示,诱导蛋白可与鼠抗His标签抗体特异性结合。口服免疫结果显示,中浓度组(2.24×10~(10) CFU/mL)和低浓度组(2.24×10~9 CFU/mL)免疫2次能够显著提高尼罗罗非鱼的血清抗体水平和抗无乳链球菌感染能力,中浓度免疫组的相对免疫保护率最高为41.0%。本研究可为罗非鱼链球菌病口服疫苗的研究奠定基础,具有广阔的应用前景。     

罗非鱼无乳链球菌微胶囊口服疫苗的研制及其免疫效果

为了建立罗非鱼无乳链球菌病免疫防控方法,以原核表达SIP(surface immunogenic protein)蛋白为芯材,天然多糖为壁材,制备罗非鱼无乳链球菌聚丙烯酸树脂Ⅱ微胶囊口服疫苗,SIP口服疫苗微胶囊颗粒平均直径约826.5μm,包封率为72.02%,载药量最高达6.11%。微胶囊包裹的SIP蛋白在5种缓冲液中释放效果:p H 6.80p H 7.20p H 9.18p H4.68p H 2.00。体外实验证实微胶囊颗粒在模拟胃酸环境中蛋白释放量极小,数值为395.5μg;而在模拟肠液中,释放量最高达5426.0μg,其中240 min释放量为4911.1μg,释放度达90.51%,说明微胶囊能避免胃酸的破坏且肠溶性好。SIP微胶囊口服疫苗以投喂的方式免疫"新吉富"罗非鱼,分别以每克罗非鱼体质量免疫5和10μg SIP蛋白的剂量分组测试,4次免疫过程中,5μg免疫剂量组特异性血清效价为100–1~400–1,10μg免疫剂量组特异性血清效价为200–1~1600–1。4次免疫后,攻毒实验表明,5和10μg的免疫剂量组的免疫保护率分别为44.45%和66.67%。研究表明,微胶囊口服疫苗免疫为罗非鱼无乳链球菌病的免疫防治提供方便、安全、有效的途径。     

饲料中海洋红酵母对尼罗罗非鱼幼鱼生长性能、消化酶及免疫酶活性的影响

为了研究海洋红酵母(Rhodotorula mucilaginosa)对尼罗罗非鱼(Oreochromis niloticus)幼鱼生长性能、消化酶及免疫酶活性的影响,配制6组饲料,分别为对照组、添加1 g·kg~(-1)、2 g·kg~(-1)、3 g·kg~(-1)、4 g·kg~(-1)和5 g·kg~(-1)的海洋红酵母组,投喂初始均质量为(5.22±0.01)g的尼罗罗非鱼,实验56 d。结果显示,与对照组相比,2 g·kg~(-1)和4 g·kg~(-1)组的饲料系数显著降低(P0.05),1 g·kg~(-1)、3 g·kg~(-1)和5 g·kg~(-1)组则没有显著性差异(P0.05)。5 g·kg~(-1)组鱼体粗蛋白含量显著低于1 g·kg~(-1)和2 g·kg~(-1)组(P0.05),1 g·kg~(-1)、3 g·kg~(-1)和5 g·kg~(-1)组鱼体粗灰分含量显著低于对照组(P0.05)。与对照组相比,1 g·kg~(-1)组胃蛋白酶活性显著升高(P0.05),3 g·kg~(-1)、4 g·kg~(-1)和5 g·kg~(-1)组胃蛋白酶活性显著降低(P0.05)。2 g·kg~(-1)和3 g·kg~(-1)组前肠和中肠淀粉酶和脂肪酶,以及肝脏溶菌酶和一氧化氮合酶活性均显著高于对照组(P0.05)。根据尼罗罗非鱼幼鱼的消化酶和免疫酶活性等指标综合分析得出,海洋红酵母在罗非鱼饲料中的建议添加量为2~3 g·kg~(-1)。     

异源无乳链球菌胞外产物灭活疫苗对罗非鱼的免疫效果

为了研究异源无乳链球菌胞外产物灭活疫苗免疫罗非鱼后的免疫效果, 本研究采用 10%甲醛溶液灭活法制备了无乳链球菌 HN0901 和 GX1101 胞外产物灭活疫苗, 通过腹腔注射途径免疫健康奥尼罗非鱼(Oreochromis niloticus♀×O.aureus♂), 在免疫后 28 d 用同/异源无乳链球菌攻毒, 测定了免疫后和攻毒后罗非鱼的免疫应答反应和血清抗体效价, 并比较了罗非鱼在腹腔注射 1×108 CFU/尾无乳链球菌后的相对免疫保护率和交叉免疫保护率。 结果显示, 免疫鱼谷丙转氨酶(ALT)和谷草转氨酶(AST)在免疫后 28 d 显著高于对照组, 但在攻毒后显著低于对照组; 与对照鱼相比, 免疫鱼的超氧化物歧化酶(SOD)和过氧化氢酶(CAT)水平在免疫和攻毒后均有不同程度的提高, 丙二醛(MDA)显著降低(P＜0.05)。实时定量 PCR 结果显示, 炎性细胞因子基因 TNF-α、IL-1β 和 TGF-β, 体液免疫相关基因 HSP70, MHC Ⅱ和 IgM 在免疫和攻毒后也呈现显著升高趋势, 并显著高于对照组(P＜0.05)。血清抗体效价于免疫后第 28 天达到 1∶6400, 显著高于对照组(P＜0.05)。攻毒实验结果显示, 免疫组在同源和异源无乳链球菌攻毒后相对的免疫保护率在 31.6%~47.4%。结果表明, 研制的灭活疫苗免疫罗非鱼后, 能够显著诱导罗非鱼体内的免疫应答, 产生中等疫苗效力, 对同/异源无乳链球菌都具有免疫保护能力。本研究结果为深入研究罗非鱼链球菌病的免疫预防技术和研制二价疫苗奠定了基础。     

不同养殖模式对尼罗罗非鱼生长、免疫性能及水质的影响

为探讨循环水养殖模式(RAS组)和池塘养殖模式(池塘组)对尼罗罗非鱼(Oreochromis niloticus)生长、免疫性能及水质影响的变化规律,开展了为期8周的养殖试验。结果表明:(1)RAS组中鱼体增重率(WGR)[(597.36±169.79)%]显著高于池塘组[(470.98±142.99)%](P0.05),饲料转化率(FCR)[(1.17±0.02)%]却显著低于池塘养殖系统[(1.47±0.03)%](P0.05)。特定生长率(SGR)和肥满度(CF)也高于池塘养殖系统,但差异不显著(P0.05);(2)在第4周和第8周分别测定了鱼体胃和肠中消化酶活性,第4周时,RAS组中肠蛋白酶活性值[(1 387.56±278.43)μg/(g·min)]显著高于池塘组[(1 129.99±382.67)μg/(g·min)](P0.05);第8周时,肠脂肪酶活性[(18.11±4.28)μg/(g·min)]显著高于池塘组[(12.89±8.00)μg/(g·min)](P0.05);(3)在第4周和第8周分别测定了鱼体肝胰脏、头肾和血清中碱性磷酸酶(ALP)、溶菌酶(LSZ)和总超氧化物歧化酶(T-SOD)活性,整体表现为RAS组免疫性能低于池塘组;(4)每周测定水体氨态氮和亚硝态氮含量显示,RAS组氨态氮维持在0.0067~0.0212 mg/L,亚硝态氮含量为0.0027~0.0087 mg/L,均低于池塘组。     

海豚链球菌感染对不同品系罗非鱼血液生化指标和肝脏HSP70 mRNA表达的影响

以吉富罗非鱼、新吉富罗非鱼、埃及尼罗罗非鱼和红罗非鱼为研究对象,饲养100d后,进行海豚链球菌(2.95×108CFU/mL)感染试验,分析攻毒前后各品系罗非鱼的血液生化指标和肝脏HSP70 mRNA表达量的变化规律。另从各桶中取20尾鱼进行同样的攻毒试验,统计攻毒后各时间点的累积死亡率。结果表明,感染海豚链球菌96h后,吉富罗非鱼和新吉富罗非鱼对病原较为敏感,累积死亡率分别达到36.67%和38.33%;埃及尼罗罗非鱼对病原敏感性较差,试验期间未见死亡。吉富罗非鱼、新吉富罗非鱼和红罗非鱼血清皮质醇和葡萄糖水平以及肝脏HSP70 mRNA的表达量在攻毒后明显提高,血清谷丙转氨酶、谷草转氨酶与溶菌酶活力也呈上升趋势,碱性磷酸酶活力与甘油三酯和胆固醇水平低于攻毒前。埃及尼罗罗非鱼可以利用糖原和脂类产生的能量,提高了HSPS与一些特定免疫蛋白(溶菌酶、球蛋白等)的合成,增强了鱼体的非特异性免疫力。罗非鱼选育过程中,需要将抗病力与生长性能进行有效的结合,在注重生长速度的同时也要增强其抗应激能力,从而为罗非鱼产业的可持续发展提供保证。     

尼罗罗非鱼CD2-like基因克隆及其胞外区表达研究

依据数据库中预测的尼罗罗非鱼白细胞分化抗原2(CD2)基因(GenBank登录号:XM_005460661.4)序列,采用PCR扩增体质量(150±50) g尼罗罗非鱼CD2分子同源类似物(CD2-like)基因编码区片段,然后以其胞外区构建原核表达质粒pGEX-6P1-CD2L,并进行原核表达及条件优化,最后进行复性纯化,为进一步研究该CD2-like分子在罗非鱼中的免疫功能奠定基础。研究结果表明,罗非鱼CD2-like(OnCD2-like)基因(GenBank登录号:MN296489)编码区全长1110 bp,其中胞外区长558 bp。构建OnCD2-like胞外区的原核表达质粒pGEX-6P1-CD2L,将该重组质粒导入大肠杆菌BL21后,成功表达OnCD2-like胞外段重组蛋白。原核表达结果显示,目的蛋白分子质量为20 ku,主要以包涵体形式存在,而该包涵体蛋白复性纯化最佳条件为:37℃下,0.2 mmol/L异丙基-β-D-硫代半乳糖苷(IPTG)诱导6 h,经梯度稀释复性并纯化后可成功获得目的重组蛋白。     

Evaluation of commercial live bakers’ yeast, Saccharomyces cerevisiae as a growth and immunity promoter for Fry Nile tilapia, Oreochromis niloticus (L.) challenged in situ with Aeromonas hydrophila

This study was carried out to evaluate the use of commercial live bakers’ yeast, Saccharomyces cerevisiae as a growth and immunity promoter for Nile tilapia, Oreochromis niloticus (L.). Fish (0.33 g) were randomly distributed at 25 fish per 140-L aquarium and fed a diet containing 0.0, 0.25, 0.50, 1.0, 2.0, or 5.0 g yeast/kg diet for 12 weeks. After the 12-week experimental period, fish of each treatment were challenged by pathogenic Aeromonas hydrophila, which was given by interperitoneal (IP) injection and kept under observation for 10 days to record clinical signs and the daily mortality rate. The growth-promoting influences of bakers’ yeast were observed with fish and the optimum growth, feed utilization, and protein turn-over were obtained with 1.0–5.0 g yeast/kg diet. Also, yeast supplementation increased protein deposition in fish body. Biochemical parameters were improved in fish fed yeast up to 1.0 g/kg diet. Total fish mortality 10-days after IP injection with A. hydrophila and its count after incubation with fish serum decreased with the increase of yeast level in fish diets. However, the lowest fish mortality and bacterial counts were obtained in fish fed 5.0 g yeast/kg. These results indicate that bakers’ yeast supplement is promising as an alternative method to antibiotics for disease prevention in tilapia aquaculture, and the optimum level of live bakers’ yeast is about 1.0 g per kg diet.     

Protection against heterologous Streptococcus iniae isolates using a modified bacterin vaccine in Nile tilapia,Oreochromis niloticus (L.)

Streptococcus iniae is a significant pathogen impacting aquaculture production worldwide. The objectives of this study were to determine whether a developed modified S. iniae (ARS-98-60) bacterin vaccine is efficacious in Nile tilapia, Oreochromis niloticus (L.), against challenge with heterologous isolates from diverse geographical locations and to evaluate protein and antigenic variability among the isolates tested. Two groups of tilapia (approximately 5 g) were intraperitoneally (IP) vaccinated with 100 μL of the vaccine or sham vaccinated with 100 μL of sterile tryptic soy broth and held for 28 days. Fish were challenged with each isolate by IP injection of 2–3 × 10⁷ CFU per fish using calcein to mark fish prior to cohabitation for challenge. The results demonstrated significant protection against all challenge isolates, and relative percent survivals ranged from 79% to 100%. SDS–PAGE analysis of whole-cell lysate proteins from the S. iniae isolates demonstrated similar protein profiles between 10 and 31 kDa and variation in profiles between 35 and 100 kDa. Western blot analysis using antiserum from vaccinated fish (ARS-98-60) demonstrated shared immunogenic proteins among all isolates in the molecular mass range of 22–35 kDa and high molecular mass material >150 kDa. The results suggest that the developed S. iniae vaccine has broad ranging protection among isolates exhibiting different protein profiles.     

盐度、碱度对尼罗罗非鱼生长和肌肉品质的影响

在水温(24±1)℃下,将初始体质量(50.00±4.12)g的尼罗罗非鱼放入150 cm×60 cm×40 cm循环可控水族缸内,每箱15尾,每组设置3个平行。将尼罗罗非鱼在盐度(12 g/L)、碱度(23.8 mmol/L NaHCO3)、盐碱(12 g/L和23.8 mmol/L NaHCO3)以及淡水(对照组)水体中分别饲养56 d,比较和测量各组鱼体生长性能指标、肌肉常规营养成分、结合氨基酸和游离氨基酸含量,研究盐度、碱度对罗非鱼生长性能和肌肉品质的影响。试验结果显示,与淡水组相比,改变水体盐度、碱度对鱼体质量增加率、特定生长率和饲料系数均无显著影响(P>0.05)。盐碱组鱼肌肉灰分含量升高,粗蛋白含量下降;粗蛋白含量显著低于其他组(P<0.05);各组水分和粗脂肪含量差异不显著(P>0.05)。各组必需氨基酸量与氨基酸总量比值和必需氨基酸与非必需氨基酸比值分别为40%~41%和66%~69%,各组间差异不显著(P>0.05);处理组中必需氨基酸指数为47.06~59.66,盐碱组>碱度组>盐度组,盐碱组显著高于盐度组和碱度组(P<0.05)。碱度组、盐碱组和盐度组鲜味氨基酸总量分别为淡水组的1.78倍、1.74倍和1.63倍,且碱度组和盐碱组显著高于盐度组(P<0.05);盐碱组甜味氨基酸和游离氨基酸总量显著高于盐度和碱度组(P<0.05)。水体盐度、碱度均可有效改善罗非鱼肌肉营养价值和呈味特征,而碱度对肌肉呈味的影响效果更加明显。     

The Effect of Different Levels of Krill Meal Supplementation of Soybean-based Diets on Feed Intake, Digestibility, and Chemical Composition of Juvenile Nile Tilapia Oreochromis niloticus, L

Abstract— The main objective of this study was to determine the effect of different levels of krill meal (KM) as a feed attractant in juvenile Nile tilapia fed soybean (SBM) diets on growth performance, feed utilization, and body composition. Fish of an initial average weight 0.8 × 0.01g were stocked in 18 glass aquaria (80 L each) at a rate of 25 fish per aquarium. Fish meal (FM 20% of the diet) was used as the sole source of animal protein in the control (Diet 1). Diets 2 to 6 had (SBM) protein with various levels of krill meal (0.0,1.5,3.0,4.5, and 6.0%, diets 2-6 respectively). Test diets were fed to satiation to triplicate groups of Nile tilapia four times daily for 20 wk. Fish fed krill meal supplemented diets had significantly ( P < 0.05) better growth performance compared with fish fed the unsupplemented and FM control diets. The krill meal increased growth of Nile tilapia by 31.9% compared to control diets (average Anal wet weight, 14.15 × 0.95 g and 10.72 × 0.2 g, respectively). Moreover, weight gains were not significantly different for fish fed diets with different levels of krill meal. Feed utilization parameters such as feed intake, feed conversion ratio, protein efficiency ratio differed significantly for fish fed krill meal diets compared with control. Digestibility of nutrient and energy of diets increased with increasing levels of krii meal. The incorporation of krill meal in diets significantly affected the protein, fat, ash, and energy of whole body composition. These results suggest that supplementation of krill meal at 1.5% in the diets of Nile tilapia as attractant or stimulant may lead to increased feed intake, growth performance, and feed utilization. Soybean meal can completely replace fishmeal in diets for juvenile tilapia.     

Compensatory growth of Nile tilapia Oreochromis niloticus,L. subjected to cyclic periods of feed restriction and feeding in a biofloc system

The compensatory growth, productive performance, proximal composition and somatic indices of Nile tilapia (Oreochromis niloticus) cultivated in biofloc were evaluated during a 144‐day period under five cyclic regimes of feed restriction and feeding. Five treatment groups, in which the frequency of feed restriction (R) and feeding (F) varied by periods (days) as follows: R1:F3, R3:F9, R6:F18, R8:F24 and R12:F36; each treatment was evaluated in triplicate. The cycles were repeated throughout the culture period. The control group received feed daily. Fish were cultivated in 18 circular tanks (3 m³) at a density of 50 fish/m³ per tank. At the end of the study, the survival of Nile tilapia was greater than 90% in all the treatments. Complete compensation in growth was achieved in R6:F18 and R12:F36. At the end of the feed restriction period, both crude protein and total lipid content of the tilapia muscle tissue taken from fish of the treatment groups were similar to samples of muscle tissue derived from fish of the control group; however, a reduction of more than 40% in somatic indices compared with the control was observed, but these recovered by the end of the feeding phase. The results indicate that cyclic feeding based on 12 days of feed restriction and 36 days of feeding (R12:F36) induced a complete compensation in weight and restoration of energy reserves, with similar measures of productive performance observed when compared to the control treatment during the culture of Nile tilapia in biofloc, and food reduction did not affect proximal composition.     

Interactive effects of dietary protein and live bakery yeast, Saccharomyces cerevisiae on growth performance of Nile tilapia, Oreochromis niloticus (L.) fry and their challenge against Aeromonas hydrophila infection

Yeasts used as a probiotic in fish diets could stimulate fish resistance against bacterial infection and could enhance the activities of digestive enzymes in fish guts. In addition to yeast importance, dietary protein is another important part in fish diets that should be carefully optimized to meet fish requirement. It is proposed that the yeast supplementation may enhance the dietary protein turnover and reduce the protein requirement for fish. Therefore, the interactive effects of dietary protein and yeast levels on the growth performance of Nile tilapia, Oreochromis niloticus (L.) fry and their challenge against Aeromonas hydrophila infection was evaluated. In the present study, ten experimental diets were formulated to contain either 35% or 45% crude protein (CP). For each protein level treatment, bakery yeast (Saccharomyces cerevisiae) was supplemented at 0.0, 0.50, 1.0, 2.0, or 5.0 g/kg diet. Fish (0.25–0.48 g) were distributed at a rate of 25 fish per 140-L aquarium. For each diet, triplicate aquaria were fed twice a day, 5 days a week for 12 weeks. Fish growth and feed utilization were significantly affected by either dietary protein or yeast levels alone, while no significant effect of their interaction was observed. The highest fish growth was obtained at 1.0–5.0 g yeast/kg diet at both protein levels; however, the fish performance at 45% CP was better than that fed on 35% CP diets. The optimum feed conversion ratio (FCR) was obtained when fish fed on 1.0–5.0 and 2.0–5.0 g yeast/kg diet at 35 and 45% CP, respectively. The cumulative fish mortality, after interperitoneal injection with A. hydrophila for 10 days, and bactericidal activity was significantly higher in fish fed 35% CP diets than those fed 45% CP diets. Both variables decreased significantly with the increase in yeast levels. The lowest bacterial count and bactericidal activity were obtained in fish fed 5.0 g yeast/kg diet irrespective to dietary protein levels. It could be concluded that the inclusion of live bakery yeast in practical diets could improve the growth performances, feed utilization, and physiological status of Nile tilapia fry and their challenge against A. hydrophila infection. Moreover, fish performance when fed 45% CP diet was better than those fed 35% CP diet. Based on these results, the most suitable yeast level for maximum Nile tilapia growth was determined to be 2.0 g yeast/kg diet with 45% CP diet; however, this level was recommended to stimulate their productive performance and enhances their resistance against A. hydrophila infection.     

Palm oil-laden spent bleaching clay as a substitute for marine fish oil in the diets of Nile tilapia, Oreochromis niloticus

A 8‐week feeding trial was conducted to determine the effect of substituting fish oil with palm oil‐laden spent bleaching clay (SBC), a by‐product from crude palm oil (CPO) refining, on growth, feed utilization, fatty acid composition and heavy metal accumulation in the muscle of Nile tilapia, Oreochromis niloticus. Four isonitrogenous and isolipidic practical diets were formulated to contain 0, 100, 200 or 300 g kg^?1 SBC. Growth performance of Nile tilapia was significantly better in fish fed the 100 g kg^?1 SBC diet compared with fish fed the 0, 200 or 300 g kg^?1 SBC diet. Growth and feed utilization efficiency of fish fed 200 or 300 g kg^?1 SBC were similar to fish fed the control diet without added SBC. Whole‐body composition, body‐organ indices and haematocrit of tilapia were not affected by dietary treatments. Fatty acid compositions in the muscle lipid of Nile tilapia were strongly influenced by dietary treatments with progressively elevated levels of total saturates and n‐6 PUFA because of the dietary influence of these fatty acids from residual CPO adsorbed onto SBC. A gradual decrease in total n‐3 PUFA concentrations were also observed with the ratio of n‐3 to n‐6 fatty acids in muscle lipids decreasing from 4.75 to 4.41, 3.23 or 2.37 after 8 weeks on the 0, 100, 200 or 300 g kg^?1 SBC diet, respectively. The arsenic, cadmium and lead concentrations in the experimental diets increased with increasing dietary levels of SBC but the concentrations of these heavy metals in the whole body and bone of Nile tilapia were not significantly different among fish fed the various diets. The present 8‐week study showed that in fishmeal‐based diets for Nile tilapia, palm oil‐laden SBC can totally replace added fish oil. The use of this presently discarded waste product from palm oil refining in tilapia diets will greatly contribute to reducing the impact of rising feed costs in the culture of tilapia in many tropical countries. Other potential benefits may include acting as a feed binder, removal of mycotoxins in fish feeds as well as adsorbing toxic substances present in the culture water.     

Complete Replacement of Fish Meal by Soybean Meal with Dietary L-Lysine Supplementation for Nile Tilapia Oreochromis niloticus (L.) Fingerlings

The effect of complete replacement of fish meal by soybean meal (SBM) with the dietary L-lysine supplementation in prepared diet was studied in Nile tilapia fingerlings. Five isonitrogenous (33.2% crude protein) and isocaloric (4.8 kcal gross energy/g of diet) diets were formulated. Diet 1 was similar to a high quality commercial tilapia diet, containing 20% fish meal and 30% SBM. Diets 2–5 contained 55%, 54%, 53%, and 52% SBM and 0.5%, 1.0%, 1.5%, and 2.0% L-lysine supplementation, respectively. After 10 wk, there was a significant difference in the final individual weight, final body length (cm), weight gain (%), specific growth rate (SGR), feed conversion ratio (FCR), protein effkiency ratio (PER), and food intake among flsh groups ( P ≤ 0.05). The best bal individual weight, final individual length (cm), weight gain (%), specific growth rate, feed conversion ratio, protein efficiency ratio (PER), and food intake were recorded in fish fed diet 2, which contained 55% SBM and 0.5% L-lysine. There was a significant difference between it and diet 1 (control). Moisture in fish flesh was not significantly different ( P > 0.05) among treatments and averaged 75.13%, while percentage protein was significantly dltrerent ( P ≤ 0.0% and the best result was achieved in flsh fed diet 2 and diet 1 (control). The highest values of digestibility coefficients of protein, fat and energy were recorded in groups of fish fed diet 2. These suggest that a diet with 55% SBM supplemented with 0.5% L-lysine can totally replace fish meal in a diet for Nile tilapia fingerlings, without adverse effect on fish performance.     

Effects of dietary probiotic Lactobacillus plantarum and whey protein concentrate on the productive parameters,immunity response and susceptibility of Nile tilapia,Oreochromis niloticus (L.), to Aeromonas sobria infection

Immunostimulatory feed supplements have an increasingly interest in aquaculture management. Generally, an individual supplement was used in fish diets but it is expected that the use of multi‐supplements may show synergistic enhancements in fish performance, health, and immunity. Therefore, the present investigation was carried out to evaluate the use of dietary probiotic Lactobacillus plantarum and whey protein concentrate (WPC) in practical diets for Nile tilapia, Oreochromis niloticus. Hence, probiotic L. plantarum, WPC and their mixture were incorporated into a basal fish diet (300 g/kg crude protein) as follows: T1 = a basal control diet, T2 = a basal diet containing L. plantarum, T3 = a basal diet containing 1.0 g WCP/kg diet and T4, T5 or T6 = basal diets containing probiotic L. plantarum + 1.0, 2.0 or 3.0 g WCP/kg diet, respectively. Fish (15.2 ± 0.6 g) were fed on one of the tested diets up to apparent satiation twice a day for 60 days. After that, fish were intraperitoneally injected with pathogenic bacteria Aeromonas sobria and fish mortality was observed for 10 days postchallenge. Fish growth and feed intake were significantly improved by dietary probiotic L. plantarum (T2) and/or WPC (T3) over the control group (T1), and highest fish performance was observed in T5–T6 fish groups. Similarly, highest values of haematocrit, glucose, total proteins, albumin, and globulin were significantly observed in T5–T6 fish groups. Likewise, fish fed dietary probiotic L. plantarum (T2), WPC (T3), and their mixture (T4–T6) showed antioxidants and immune‐stimulating activities better than the control group. Fish fed the control diet were more susceptible to A. sobria infection showing highest fish mortality (75.0%). Meanwhile, dietary probiotic L. plantarum (T2), WPC (T3), and their mixture (T4–T6) enhanced significantly the fish resistance to A. sobria infection resulting in maximum values of relative percent of fish survival (73.3%–80.0%) in T5–T6 groups. The present investigation recommended the use of probiotic L. plantarum with 2.0 g WPC/kg diet to improve the growth, antioxidant, immunity responses and tolerance of Nile tilapia to A. sobria infection.