红鳍东方鲀稚鱼肠道可培养细菌的多样性

使用2216E平板涂布法从肠道样品分离可培养细菌,通过16S r DNA测序鉴定细菌。所有分离的细菌分为变形菌门(包含γ-变形细菌纲和α-变形细菌纲)和厚壁菌门。其中以γ-变形细菌纲为优势(83.3%)。在属的水平,从肠道中共分离出弧菌属、希瓦氏菌属、假交替单胞菌属、亚硫酸杆菌属、芽孢杆菌属、Aliivibrio、发光杆菌属、科尔韦尔氏菌属8个属,其中弧菌属、希瓦氏菌属和假交替单胞菌属的种类占总数的70%。首次发现亚硫酸杆菌属和科尔韦尔氏菌属作为红鳍东方鲀稚鱼肠道菌群的一部分。     

应用RFLP和DGGE技术分析工厂化养殖凡纳滨对虾肠道微生物群落特征

本研究应用PCR-RFLP(Polymerase Chain Reaction-Restriction Fragment Length Polymorphism)和PCR-DGGE(Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis)技术,对工厂化养殖的凡纳滨对虾肠道菌群进行多样性分析。RFLP结果显示,8月样品中不同的克隆子为5个,其中以不可培养细菌(Unculturable bacteria)为主要优势菌,其次为鲁杰氏菌属菌种Ruegeria spp.和Rhodobacterales spp.。依据微生物多样性的覆盖率分析结果表明,所构建16S rDNA克隆文库的覆盖率为97.5%。10月样品中克隆子为8个,其中以不可培养细菌、芽孢杆菌属Bacillus spp.和弧菌属Vibrio spp.为主要优势菌属,其次为Photobacterium spp.和Neptunomonas spp.;所构建16S rDNA克隆文库的覆盖率为90.8%。应用DGGE分析8月和10月对虾肠道样品,菌群以不可培养细菌和弧菌属为主,其次为Streptomyces spp.、Ruegeria spp.、Enterococcus spp.和Photobacterium damselae。     

大连两个海区海带相关可培养细菌群落分析

为研究大连两个海区海带相关可培养细菌群落,于2014年12月和2015年3月分别自登沙河湾和正明寺海带养殖区采集健康海带孢子体和海水,采用2216E涂布平板法,共分离出240株细菌,对所有菌株进行PCR和16S rDNA测序。结果表明,120条海带相关序列归属为4个门、5个纲、8个目、15个科、19个属、42个种;120条海水序列属于4个门、6个纲、10个目、18个科、26个属,46个种。在门水平,海带相关和海水细菌群落均可分为变形菌门、厚壁菌门、放线菌门和拟杆菌门,其中变形菌门和厚壁菌门为优势门。在属水平,海带相关优势属为嗜冷杆菌属、假单胞菌属、副球菌属和Salinibacterium;海水相关优势属为芽孢杆菌属、假单胞菌属、动球菌属、假交替单胞菌属和弧菌属。只从海带分离出的细菌属于微杆菌属、微小杆菌属、黄杆菌属、短小杆菌属、肠杆菌属、寡养单胞菌属和原小单孢菌属。Srensen指数表明,两个海区海带细菌群落有一定差异,不同海区海水及同一海区海带与海水细菌群落明显不同。     

紫菜养殖对养殖水体中细菌多样性分布及环境因子的影响

采用基于16S rDNA的高通量测序技术对山东长岛紫菜养殖区的细菌多样性分布进行了研究,并与环境因子进行关联分析,以探究紫菜养殖对环境的影响。结果显示,长岛海区水环境细菌多样性较丰富,呈现由近岸区(CDCNS)、养殖区(CDPF)、外海区(CDCOS)递减的趋势。分别基于所有细菌组成以及相对丰度最高的前20个属/种的聚类结果均显示,CDCNS和CDCOS区聚在一起,明显区别于CDPF区。CDPF区的特异优势菌包括鼠尾菌属(Muricauda)、假单胞菌属(Pseudomonas)、盐单胞菌属(Halomonas)、赤杆菌属(Erythrobacter)、海杆菌属(Marinobacter)。3个区域均未检测到河豚毒素假交替单胞菌(Pseudoalteromonas tetraodonis)、柠檬假交替单胞菌(Pseudoalteromonas citrea)等疑似紫菜致病菌。溶解氧(DO)和pH呈现由近岸向外海逐渐降低的趋势,总颗粒悬浮物(TSS)反之。CDPF区氨氮(NH4+-N)含量最低,盐度最高。关联分析发现,环境因子与环境微生物之间具有一定的相关性,如嗜氨菌属(Ammoniphilus)的丰度与NH4+-N 浓度具显著正相关性,CDPF区最低,CDCOS区最高;盐单胞菌属的分布与盐度具显著正相关性,CDPF区盐单胞菌属含量显著高于其他2个海区。研究表明,紫菜养殖海区细菌群落结构特征与环境因子具有关联性,其间的互作机制尚需进一步深入研究。     

5种海水养殖石首鱼类肠道菌群多样性的比较

为探究海水养殖石首鱼类肠道菌群的结构特征及宿主遗传因素对肠道菌群的影响,实验采用基于Illumina Hiseq2500测序平台的高通量测序技术,对福建宁德三都澳养殖的5种石首鱼类(大黄鱼、黄姑鱼、状黄姑鱼、和眼斑拟石首鱼)的肠道菌群进行16S rDNA V3～V4区测序分析。各样本得到unique tags的数目为20 351～43 347个,上述5种鱼类分别得到479、626、603、518和556个操作分类单元(OTUs),分类注释结果显示,这些OTUs可划归33门273属。5种石首鱼类肠道内容物和肠道壁样品均以变形菌门、拟杆菌门和厚壁菌门细菌为主要优势菌群,约占总菌量的70%,在大黄鱼肠道菌群中,螺旋菌门细菌占比达26.19%,也是其主要优势菌群。在属分类水平上,芽孢杆菌属、发光杆菌属、弧菌属、金黄杆菌属、鞘氨醇单胞菌属及假单胞菌属等属细菌是5种养殖石首鱼类的主要类别。肠道菌群多样性的分析表明,Shannon多样性指数：黄姑鱼>状黄姑鱼>眼斑拟石首鱼>>大黄鱼,这些养殖石首鱼类的肠道内容物菌群的多样性均高于肠道壁。对上述鱼类种间的肠道菌群差异性分...     

一株引起香鱼出血症的嗜水气单胞菌的鉴定

从发生出血症的香鱼体腔液分离到一高致病性的菌株(ayu-ah0201),经人工侵染试验证实该菌能引起香鱼出血症.对该菌的形态、生理生化及16S rDNA序列分析结果表明,其为革兰氏阴性,短杆状,极生鞭毛.对蔗糖、阿拉伯糖、七叶苷、氧化酶、精氨酸双水解酶、赖氨酸脱羧酶呈阳性,鸟氨酸脱羧酶呈阴性.可利用葡萄糖产酸产气.在以该菌16S rDNA序列和GenBank数据库内同源性较高的细菌16S rDNA序列构建的系统发育树,表明分离菌ayu-ah0201与嗜水气单胞菌聚在一簇,与嗜水气单胞菌核苷酸序列同源性最高,为99.6%～99.7%,与其他相关气单胞菌属成员的核苷酸序列同源性小于98.9%.结合形态和生理生化特点将其鉴定为嗜水气单胞菌.     

美洲鳗鲡及其养殖水体分离耐药菌的多样性和耐药性分析

为了更有针对性地防控水产动物细菌性病害的发生和流行,本实验对美洲鳗鲡及其养殖水体耐药细菌的种属特征及耐药情况开展了相关研究。首先采集美洲鳗鲡不同部位(表皮、鳃、肠道)及其养殖水体的样品,经5种抗菌药物平板筛选耐药菌株,然后采用K-B纸片扩散法检测细菌对抗菌药物的耐药性,同时测定耐药菌株的16S rDNA序列,进而分析耐药菌的种属分布和多重耐药性。结果显示,经耐药平板筛选分离纯化得到108株细菌,分别属于气单胞菌属、柠檬酸杆菌属、不动杆菌属等20个属;其中,93.5%的菌株对3种(含)以上的抗菌药物具有耐药性,86.1%的菌株对3类(含)以上的药物具有抗性。对阿莫西林的耐药率高达90.7%,对四环素、利福平以及磺胺类和酰胺醇类药物类的耐药率为60%~80%,对头孢噻肟、新霉素以及喹诺酮类的耐药性弱(低于20%)。美洲鳗鲡肠道(0.40)、表皮(0.41)、鳃部(0.42)及水样(0.47)菌群的多重耐药指数显示各生态样品耐药程度较为严重,尤以水样为最。各菌属中,柠檬酸杆菌属(0.58)和克雷伯菌属(0.61)的多重耐药指数最高,而不动杆菌属(0.21)则相对较低。美洲鳗鲡及养殖水体普遍存在多重耐药菌株,对此应引起足够的重视;水产动物及养殖环境耐药细菌对某些水产用药如诺氟沙星、新霉素等耐药率低,可将其做为水产动物细菌性疾病治疗的首选药物。     

江苏近海海域好氧菌类群组成分析

在对江苏近海海域好氧菌进行调查中,选择了ZD-B287（N119°35′E34°40′）和JC-H187（N121°53′E32°20′两个采样点,分别在春、夏、秋、冬进行了4次水样和底层表面泥层样品采集。以随机挑选的方法分离、纯化了395株海洋好氧细菌,运用16SrDNA基因序例进行鉴定。通过NCBI的BLAST检索系统进行序列同源性比较,与GenBank数据库中获得菌株的16SrDNA基因序列进行多序列匹配排列。得到13株可培养的好氧菌,分别为假交替单胞菌属（Pseudoalteromonas）、假单胞菌属（Pseudomonas）、微小杆菌属（Exiguobacterium）、芽孢杆菌属（Bacillus）、弧菌属（Vibrio）、红细菌属（Rhodobacter）、海杆菌属（Marinobacter）、伯克霍尔德菌属（Burkholderia）、海洋单胞菌属（Marinomonas）、动性微菌属（Planomicrobium）、变形杆菌属（Proteus）、玫瑰杆菌属（Roseobacter）和交替单胞菌属（Alteromonas）。     

草鱼养殖模式对气单胞菌属细菌群落影响分析

为研究草鱼池塘精养、山塘养殖以及鱼菜共生养殖3种养殖模式下气单胞属细菌群落特征差异,2017年5—7月(养殖投喂旺盛期)用采水器在池塘两端和中部采集表层15 cm处水样,混合均匀后,装入灭菌塑料瓶中,低温保存;在池塘两端和中部用采泥器采集表层底泥,现场各无菌称取5 g底泥,置于装有135 mL的无菌生理盐水的塑料瓶中,振荡混匀,低温保存。水样和底泥样4 h内带回实验室,利用RS平板分离法分离水体和底泥样本中的细菌,通过16S rDNA测序方法鉴定、分析分离细菌。试验结果表明,共分离细菌54株,为10属22种,其中气单胞菌属23株,假单胞菌属8株,柠檬酸杆菌属6株,肠杆菌属7株,泛菌属、沙雷氏菌属各3株,果胶杆菌属、沙门氏菌属、克吕沃尔菌属、勒克氏菌属细菌各1株。按细菌种类分,维氏气单胞菌数量最多,为12株,嗜水气单胞菌次之,为10株,烟粉肠杆菌6株,弗氏柠檬酸杆菌5株,其他细菌1～2株不等。不同养殖模式下细菌种类和数量分析表明,鱼菜共生养殖系统细菌种类和数量最多,达到12种21株,潜在致病菌占比较少,草鱼精养殖池塘细菌种类最少,为5种13株,致病菌占比较高。细菌环境分布特征表明,维氏气单胞菌多分布在水体,嗜水气单胞菌多分布于底泥中。     

智利竹鱼渔场海洋微生物的物种多样性及其生物活性筛选

利用东海水产研究所开展的2012年东南太平洋智利竹鱼(Trachurus murphyi)渔场生态环境调查,对该海域75个站点进行了海洋微生物样品的采集;通过菌株的16S rRNA测序及GenBank数据库比对,分析了从所采样品中分离获得的海洋微生物菌株的物种多样性;通过菌株发酵、代谢产物提取及其抗菌滤纸扩散分析,对其发酵代谢产物粗提物进行了抗菌活性筛选;通过类胡萝卜素合成通路中八氢番茄红素合成酶(crtB)及脱氢酶(crtI)基因分析,对筛选到的抗菌活性菌株进行了基因筛选。结果表明,累计分离获得可培养海洋微生物菌株628株,其隶属12个属,其中的优势菌属包括亚硫酸盐杆菌属(Sulfitobacter)、弧菌属(Vibrios)及气单胞菌属(Aeromonas)。其中16株菌株的发酵代谢产物具有明显的抗菌活性,而其中12株活性菌株具有合成类胡萝卜素的crtB、crtI分子遗传基础。     

Cross-protection of a live-attenuated Flavobacterium psychrophilum immersion vaccine against novel Flavobacterium spp. and Chryseobacterium spp. strains

For salmonid producers, a common threat is Flavobacterium psychrophilum. Recent advancements in bacterial coldwater disease (BCWD) management include the development of a live-attenuated immersion vaccine that cross-protects against an array of F. psychrophilum strains. Emerging family Flavobacteriaceae cases associated with clinical disease have been increasing, including pathogenic isolates of Flavobacterium spp. and Chryseobacterium spp. The cross-protective ability of a live-attenuated F. psychrophilum vaccine was determined against three virulent Flavobacteriaceae isolates. Juvenile rainbow trout were vaccinated, developed high F. psychrophilum-specific antibody titres and were challenged with Chryseobacterium spp. isolates (S25 and T28), a Flavobacterium sp. (S21) isolate, a mixed combination of S21:S25:T28, and a standard virulent F. psychrophilum CSF259-93 strain. Results demonstrated strong protection in the CSF259-93 vaccinated group (relative per cent survival (RPS)=94.44%) when compared to the relevant CSF259-93 controls (p < .001). Protection was also observed for vaccinated fish challenged with the S21:S25:T28 mix (RPS = 85.18%; p < .001). However, protection was not observed with the S21, S25 or T28 isolates alone. Analysis of whole-cell lysates revealed differences in protein banding by SDS-PAGE, but conserved antigenic regions by Western blot in S25 and T28. Results demonstrate that this live-attenuated vaccine provided protection against mixed flavobacterial infection and suggest further benefits against flavobacteriosis.     

添加外源益生菌对大菱鲆育苗生物饵料菌群结构的影响

为评价在大菱鲆育苗生产中添加外源益生菌对生物饵料轮虫和卤虫微生物菌群结构的影响,运用基于illumina HiSeq平台的高通量测序技术对添加益生菌和按照生产流程正常强化的轮虫、卤虫进行了菌群结构的分析和对比。添加外源益生菌的实验组轮虫和卤虫中的菌群物种多样性均明显高于对照组。在轮虫强化过程中,不同时期的对照组样品中菌群结构差异较明显,优势细菌种类变化较大。而添加外源益生菌后的各时期实验组轮虫菌群结构很相似,优势菌群的种类更为丰富,Lactococcus sp.、Pseudoalteromonas sp.和Alteromonas sp.等一直是各实验组中的优势细菌。在卤虫强化过程中,各对照组样品的菌群结构高度相似,优势细菌Cobetia sp.的相对丰度高达54%~65.2%。而在添加益生菌后,各实验组中的菌群结构仍高度相似,但Cobetia sp.的比例下降至4.3%~25.3%,最优势的细菌为Pseudoalteromonas sp.和Alteromonas sp.等几种,菌群结构中的物种均匀度更好。研究表明,在轮虫和卤虫强化过程中添加外源益生菌,能够改变生物饵料的菌群结构,使生物饵料中的细菌种类均匀度更好,并使菌群结构趋于稳定。     

Genetic variation in mitochondrial genes and intergenic spacer region in harmful algae <Emphasis Type="Italic">Chattonella</Emphasis> species

In this study, nuclear ribosomal RNA gene internal transcribed spacer regions and the cox2-cox1 fragment of the mitochondrial (mt) genome were sequenced in 24 strains of Chattonella spp. Variability in both regions showed that the mt genome sequences of Chattonella spp. have a higher evolutionary rate than the nuclear rRNA gene sequences. A maximum likelihood tree based on the mt sequence grouped the Japanese Chattonella strains into two groups (Groups A and B), although no correlation was observed amongst the phylogenetic groups, their morphologies, or the isolated areas. Groups A and B were clearly identified by a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay using Fokl, without the need for a sequencing experiment. The PCR-RFLP assay revealed that Chattonella cells obtained from sea water in Oita, Japan, in 2004 and 2005 belonged to Group B. This is the first report showing the genetic variation in Chattonella spp. using a PCR-RFLP identification protocol.     

Susceptibility of corkwing wrasse Symphodus melops, goldsinny wrasse Ctenolabrus rupestis, and Atlantic salmon Salmo salar smolt, to experimental challenge with Vibrio tapetis and Vibrio splendidus isolated from corkwing wrasse

The virulence of two Vibrio strains, previously isolated from diseased corkwing wrasse Symphodus melops and identified as V. tapetis and V. splendidus, to corkwing and goldsinny wrasse Ctenolabrus rupestris and to Atlantic salmon Salmo salar, was studied under laboratory conditions. Both bacteria were shown to be opportunistically pathogenic to corkwing wrasse, causing significantly higher mortality in the challenged groups than in the controls. Bacterial cultivation of kidney samples and re-isolation of V. tapetis and V. splendidus from most mortalities confirmed the two strains as the probable cause of mortality in the challenged groups. The control group also suffered relatively high mortality, but no specific pathogens that were suspected to be the main cause of death were isolated, other than a mixture of Vibrio spp. and, in the case of one individual, atypical Aeromonas salmonicida. Following injection challenge with both bacterial strains, no mortality was recorded in Atlantic salmon. In bath challenge trials with goldsinny wrasse, only slight mortality was observed in the challenged groups and the unchallenged control group. Bacterial examination showed that atypical Aeromonas salmonicida was the probable cause of death in both bath challenged and control groups of goldsinny wrasse, and no indication of infection by any Vibrio sp. was found.     

Use of Microbacterium sp. and Exiguobacterium mexicanum to improve the survival and development of Artemia under xenic conditions

The effect of Microbacterium sp. strain 8L and Exiguobacterium mexicanum strain 8N was evaluated in the diet of Artemia under xenic conditions. Viable cultures of bacteria were provided to xenic cultures of Artemia in combination with Sacharomyces cerevisiae, cornflour or Spirulina, and the effect on the survival and growth was recorded. The use of these bacterial strains improves significantly the survival of Artemia independently of the used food (P < 0.05), and variable results were observed in the growth.     

怀头鲇体表溃烂症病原鉴定及致病性分析

为探讨黑龙江流域怀头鲇体表溃烂症的病因及防控措施,本研究采用常规方法从患病鱼的肝脏、脾脏和肾脏等部位分离病原菌,通过人工感染试验确定分离菌株的致病性,并对菌株的基本形态、理化特性、分子特征、毒力基因携带情况及耐药性等进行了系统研究。结果显示,从患病鱼体内分离得到3株病原菌,分别命名为NY-8、NY-9和NY-12;人工感染试验发现,NY-8和NY-9株对试验鱼有较强的致病力,NY-12株毒力较弱;3株细菌混合感染后,鱼体发病症状与临床自然发病症状一致,试验鱼死亡率高达到100%。综合理化特征和16S r RNA基因序列分析结果,确定NY-8、NY-9和NY-12株分别为气单胞菌属的维氏气单胞菌、杀鲑气单胞菌和嗜水气单胞菌。5种毒力基因在3株气单胞菌中的分布表现为两种基因型,h l y+/a e r+/a c t+/a l t+/G C A T+和h l y+/a e r-/act+/alt+/GCAT+,同时携带5种毒力基因的NY-8和NY-9分离株致病性显著高于NY-12株。3株细菌在耐药谱上有一定差异性,NY-8和NY-9株均对4种氟喹诺酮类药物敏感,对氨基糖苷类、呋喃类等药物耐药;NY-12株仅对左氧氟沙星和氟苯尼考等2种药物敏感。     

Diversity of bacteria in sewage treatment plant used as fish culture pond in southern Ghana

Bacterial populations from different stages of sewage treatment ponds in Ghana have been found to consist essentially of the same bacterial species, but the predominant species varied with each system. Subtyping of the bacterial strains recovered from the different ponds, and comparing the species present was a valuable tool in determining correlations between the flora of the different environments. The results indicated that the diversity among the bacteria populations from the sewage treatment ponds was generally high, with mean diversity above 0.95 in each pond. Twenty‐five species of bacteria were identified as associated with the fish culture systems in this study. The identified bacteria included one genus of spiral and curved bacteria, Campylobacter sp., one genus of Gram‐negative aerobic rod, Pseudomonas sp., 16 genera of Gram‐negative facultative anaerobic rods, Actinobacillus sp., Aeromonas sp., Citrobacter sp., Edwardsiella sp., Enterobacter sp., Escherichia sp., Flavobacterium sp., Hafnia sp., Klebsiella sp., Pasteurella sp., Proteus sp., Salmonella sp., Serratia sp., Shigella sp., Vibrio sp. and Yersinia sp., one Gram‐negative anaerobic bacterium, Bacteroides sp., three Gram‐positive cocci, Micrococcus sp., Staphylococcus sp. and Streptococcus sp., two endospore‐forming rods, Bacillus sp. and Clostridium sp., and one Actinomycete, Corynebacterium sp.     

Methods for identification and differentiation of different Shewanella spp. isolates for diagnostic use

Shewanella spp. are Gram‐negative, rod‐shaped, motile bacteria that are widely distributed in marine and freshwater environments. The bacteria are present in the physiological microflora of fish from temperate waters and are known as fish spoilage species. From clinically healthy fish and from fish with skin ulcerations, Shewanella spp. is regularly isolated, indicating a possible role as fish pathogen. In this study, 74 isolates of Shewanella spp. were analysed. For species identification, biochemical techniques, 16S rRNA sequencing, MALDI‐TOF MS and the Sherlock Microbial Identification System (MIS) based on the composition of fatty acid ethyl esters were compared. The phylogenetic relationship, cytotoxicity in vitro and resistance against antibiotics were tested. The most reliable method for species identification was 16S rRNA sequencing. From diseased fish, clinically healthy fish and the aquatic environment, different Shewanella species were isolated. This indicates that Shewanella spp. is widespread in the aquatic milieu and acts as a secondary pathogen. The virulence of Shewanella spp. is probably not depending on the species but on the isolate itself. Many isolates of Shewanella spp. were showing multiresistances against antibiotic substances, especially in samples derived from retailers and in routine diagnostics, all Shewanella spp. should therefore be tested for resistances against antibiotic agents.     

凡纳滨对虾肠道内产消化酶益生菌的分离与筛选

为获得具有消化酶活性且安全的益生菌,从凡纳滨对虾肠道中初步分离得到576株细菌,对菌株进行产蛋白酶、淀粉酶和脂肪酶能力的定性及定量测试,筛选出产酶种类多且产酶能力强的菌株11株。对筛选出的11株菌进行了幼虾浸浴实验、药敏性实验和溶血性实验,以评价其生物安全性。将11株菌的菌悬液添加到凡纳滨对虾幼虾的养殖水体中进行浸浴实验,浸浴结束后用鳗弧菌进行刺激,测定不同浸浴组幼虾相关免疫基因的相对表达量,以确定其对幼虾的保护效果。综合消化酶活性、菌株对幼虾的保护效果及生物安全性,筛选得到4株效果较好的菌株。菌株的16S r DNA分子鉴定结果表明,细菌1号、2号和4号分别与芽孢杆菌(Bacillus sp.PCSAS2-38,GQ284495.1)、蜡样芽孢杆菌(B.cereus strain N419,JN400121.1)及苏云金芽孢杆菌(B.thuringiensis strain EA26.1,KC758847.1)的相似性均为100%,9号菌株与荚膜红细菌(Rhodobacter capsulatus strain PSB-03,FJ866782.1)相似性达到99%,为后续益生菌制剂的开发奠定了前期基础。     

Colonization of the gut in first feeding turbot by bacterial strains added to the water or bioencapsulated in rotifers

Two bacterial strains, 4:44 and PB52, isolated from turbot(Scophthalmus maximus L.) were used during a first feedingexperiment with turbot larvae. Bacteria were either added directly tothe water on the day of hatching of the larvae (day 0), orbioencapsulated in rotifers (Brachionus plicatilis) distributedon day 2 after hatching. The two bacterial strains were found to bepresent in the water of the rearing tanks throughout the experiment. Theaddition of bacteria influenced the species-composition of themicroflora associated with intensively produced rotifers added to thetanks, and resulted in colonization of the gut of the larvae by theadded bacterial strains. The strain 4:44 showed a peak on day 9 afterhatching, and reached a mean(sem) of 2.5(1.4) × 10⁴bacteria per larva, when added in a mixture with PB52, and 0.4(0.1)× 10⁴ bacteria per larva, when added alone. The strainPB52, on day 12 after hatching, reached 5.2(1.5) × 10⁴bacteria per larva when added in a mixture with strain 4:44, and12.5(0.7) × 10⁴ bacteria per larva, when added alone.The added bacteria colonized the gut turbot larvae, whereas thebacterial land, the survival and growth of the larvae were in most casesnot influenced in a negative way by the addition of bacteria.