两种养殖模式下黄条鰤幼鱼消化道菌群对生长的微生态调控作用

探究了工厂化、网箱养殖模式对黄条鰤(Seriola lalandi)幼鱼生长性能及消化道菌群的影响, 通过 16S rRNA 高通量测序和生物信息学方法, 分析了两种养殖模式下黄条鰤幼鱼消化道(胃、幽门盲囊、肠道)、饵料及养殖水中的菌群结构特征及其互作关系。结果显示, 本实验条件下, 网箱养殖黄条鰤幼鱼较工厂化养殖鱼生长性能显著提升; 在黄条鰤幼鱼消化道菌群方面, 门水平上的拟杆菌门(Bacteroidetes)、厚壁菌门(Firmicutes)和属水平上的拟普雷沃氏菌属(Alloprevotella)、拟杆菌属(Bacteroides)在网箱养殖模式中其丰度值高于工厂化养殖模式, 其中拟杆菌属仅出现于网箱养殖模式且呈现显著性差异; Beta 多样性分析显示消化道菌群更多受到饵料菌群的影响, 受水环境影响相对较小。KEGG 注释分析表明两种养殖模式的差异菌群中, 网箱养殖幼鱼消化道菌群主要参与磷酸转移酶系统 (PTS)和 NOD 样受体信号通路, 而工厂化养殖幼鱼为碳水化合物代谢和类胡萝卜素合成通路。本研究表明, 环境菌群中, 饵料菌群对消化道菌群的影响大于养殖水体菌群; 消化道微生物群落通过调整其组成结构从而改变菌群功能通路的方式, 积极参与两种养殖模式下黄条鰤幼鱼生长机能差异的调控。因此, 网箱养殖鱼表现出更快速的生长性能可能是由于机体内的菌群产生了更多的短链脂肪酸并诱导 IGF-1 等生长相关功能基因的表达, 从而促进机体的营养吸收和生长。本研究预期结果将为黄条鰤专用配合饲料的研制和健康养殖技术开发提供微生态理论支撑。     

不同养殖模式黄鳝胃肠道微生物群落结构分析

为探究不同养殖模式下黄鳝(Monopterus albus)胃肠道微生物的群落结构，本实验采用16S rRNA高通量测序技术研究虾塘散养、蟹塘散养、网箱投喂鱼浆和网箱投喂水蚯蚓4种养殖模式下黄鳝胃肠道微生物的组成和群落结构。Alpha多样性分析和Venn图结果显示，网箱投喂水蚯蚓组黄鳝胃肠道微生物多样性和丰度均较高，而蟹塘散养组最低。除蟹塘散养组黄鳝肠道的优势菌为变形菌门，其余3种养殖模式黄鳝胃肠道优势菌群均为厚壁菌门，推测黄鳝胃肠道微生物的核心菌群为厚壁菌门。在属水平上，网箱投喂水蚯蚓养殖模式中黄鳝胃的优势菌群为粪杆菌属(Faecalibacterium)与嗜黏蛋白阿克曼菌属(Akkermansia),其余3种养殖模式中黄鳝胃的优势菌群都为韦荣球菌属(Veillonella);而虾塘散养组黄鳝肠道的优势菌群为瘤胃球菌属(Ruminococcus),其余3种养殖模式的优势菌群中都有双歧杆菌属(Bifidobacterium)。结果表明：网箱投喂水蚯蚓组黄鳝胃肠道微生物多样性和丰度均较高，且益生菌群占比高，潜在致病菌较少，是比较健康的养殖模式。     

北方吊笼养殖刺参肠道及其养殖环境菌群结构特征及其相关性分析

为探究北方吊笼养殖刺参(Apostichopus japonicus)肠道及其养殖环境菌群结构的关系，本研究基于高通量测序技术全面解析刺参肠道和养殖环境菌群结构和功能特征，并初步探讨刺参肠道及其养殖环境菌群相关性。结果显示，刺参肠道菌群丰度和多样性均显著高于养殖水体(P<0.05)。刺参肠道及养殖水体主要优势菌门均隶属于变形菌门(Proteobacteria)和拟杆菌门(Bacteroidetes)，二者存在13个相对丰度大于0.1%的共有核心菌属。此外，肠道菌群具有一定的独立性，其特异性菌群主要隶属于厚壁菌门(Firmicutes)和绿弯菌门(Chloroflexi)，以芽孢杆菌属(Bacillus)、乳酸杆菌属(Lactobacillus)、海泥海球菌属(Halioglobus)、Lutimonas和Woeseia为代表。基于KEGG代谢通路数据库，共注释到300条三级代谢通路，其中146条存在极显著差异(P<0.001)。刺参肠道菌群差异代谢通路主要表现在代谢方面，具体表现为碳水化合物消化吸收、蛋白质消化吸收和鞘脂类代谢。研究表明，刺参肠道菌群种类与其养殖水体呈高度相似性，但相对丰度存在显著性差异。本研究结果可为北方刺参吊笼健康养殖提供一定的理论依据。     

工厂化循环水养殖条件下云纹石斑鱼消化道产酶菌的分离鉴定

采用16S r DNA-PCR菌群分离鉴定的方法,对循环水养殖条件下云纹石斑鱼(Epinehelus moara)幼鱼的胃、幽门盲囊、前肠、中肠和后肠的菌群结构进行了鉴定,用产酶菌筛选培养法对产消化酶的菌株进行了分离鉴定,并测试了各菌株消化酶的活力。研究发现,云纹石斑鱼幼鱼消化道内可培养的主要菌群为假单胞菌属(Pseudomonas)、微小杆菌属(Exiguobacterium)、不动杆菌属(Acinetobacter)、寡养单胞菌属(Stenotrophomonas)和葡萄球菌属(Staphylococcus),其中产消化酶的菌株占可培养菌的55.6%。在产酶菌中,同一株菌产3种酶的有5株;产2种酶的有9株;中肠和后肠的菌株数最为丰富,胃次之,幽门盲囊和前肠菌群种类较少;产脂肪酶的菌株都集中在中肠。产消化酶的菌株主要以产蛋白酶和淀粉酶为主,且产酶量丰富,产蛋白酶活力最高达(87.732±1.134)U/m L;淀粉酶活力为(77.176±0.599)~(73.458±0.574)U/m L;产纤维素酶的菌仅一株,且酶活力较低。分析得知,消化道的菌群结构直接影响了外源性消化酶的种类与活性。本研究为工厂化循环水养殖条件下产酶有益菌的筛选提供了理论依据。     

养殖花鲈（Lateolabrax maculatus）肠道菌群的多样性分析

为探究养殖花鲈(Lateolabrax maculatus)肠道菌群的结构特征,采用Illumina Hiseq2500高通量测序技术,对福建宁德三都澳网箱养殖花鲈的肠道内容物及肠壁菌群16S r DNA V3-V4区进行测序。肠道内容物和肠壁样品分别获得456和293个OTUs(operational taxonomic units),分属22个门120个属。花鲈肠道菌群以厚壁菌门(Firmicutes)、变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)和梭杆菌门(Fusobacteria)细菌为主要优势菌群,分别占其肠道菌群数量的47.2%、25.8%、14.4%和10.3%。在属分类水平上,发光杆菌属(Photobacterium)、梭菌属(Clostridium)及鲸杆菌属(Cetobacterium)等属细菌是主要类别。对养殖花鲈的肠道内容物与肠壁菌群进行比较分析显示,肠壁菌群多样性略高于肠道内容物。肠道内容物中,发光杆菌属、梭菌属及鲸杆菌属等是主要菌属,其中鲸杆菌属和梭菌属分别占肠道内容物菌群总菌数的17.8%和12.5%,为主要标志性差异种类;在肠壁样品的菌群中,乳球菌属(Lactococcus)、真杆菌属(Eubacterium)、Lachnoclostridium、弓形菌属(Arcobacter)和Flavonifractor为丰度较高的菌属,其中格氏乳球菌(Lactococcus garvieae)为主要标志性物种,占肠壁菌群总数的5.6%。在花鲈肠壁上定殖着格氏乳球菌(L. garvieae)和美人鱼发光杆菌(Photobacterium damselae subsp. damselae)等条件致病菌,因此,在养殖中需要注重饵料及环境的管理,避免致病菌大量增殖引起暴发性鱼病。     

野生与养殖银鲳消化道菌群结构中产酶菌的对比分析

实验对野生和养殖银鲳胃、幽门盲囊、前肠、中肠、后肠菌群结构进行了定性对比分析,并对产蛋白酶、淀粉酶、脂肪酶、纤维素酶的菌株进行了鉴定。结果发现,野生和养殖种群的消化道菌群结构存在较大差异,且同一种群消化道各部分之间菌群结构也存在较大差异。尽管养殖和野生银鲳均在幽门盲囊中具有最多的可培养细菌菌株,但野生银鲳消化道内主要菌群为嗜冷菌属(Psychrobacter)和Pseudochrobactrum,养殖银鲳消化道主要菌群为不动杆菌属(Acinetobacter)和假单孢菌属(Pseudomonas),两种群共有细菌仅一株,即Psychrobacter piscatorii strain VSD503,但其分别存在于野生与养殖种群银鲳消化道的不同部位。在产酶菌株筛选中发现,野生银鲳消化道内分离到16株产酶菌,其中44%可培养菌能产蛋白酶,56%能产淀粉酶,11%能产脂肪酶,56%能产纤维素酶,部分菌株可产2株以上的消化酶,其中产3种以上酶的菌株有5株,且产酶量丰富。相对于野生银鲳,养殖银鲳消化道内分离到22株产酶菌,主要以产蛋白酶和淀粉酶为主,70%可培养菌可产蛋白酶,21%可产淀粉酶,仅Bacillus thuringiensis strain VITGS可产纤维素酶,无一株菌产脂肪酶,其中只有Bacillus thuringiensis strain VITGS产3种酶但产酶量相对较少。研究可为银鲳人工养殖中潜在益生菌的筛选提供理论依据。     

稻田和池塘两种模式下金边鲤与建鲤肠道菌群 差异分析

利用MiSeq高通量测序技术测定16S rRNA基因序列,分析比较池塘金边鲤、稻田金边鲤、池塘建鲤和稻田建鲤4组鲤鱼肠道菌群的结构组成和丰度差异。试验结果显示,池塘金边鲤组、稻田金边鲤组、池塘建鲤组和稻田建鲤组分别获得了377、250、367和455个运算分类单元,其中运算分类单元聚类分析发现,稻田建鲤组与另外3组差异最大;菌群多样性分析发现,池塘金边鲤组的辛普森指数显著高于其他3组(P0.05),而稻田建鲤组及稻田金边鲤组的香农指数分别为1.56±0.22和2.53±0.82,均高于对应的池塘组,但差异不显著(P0.05);此外,池塘金边鲤组中变形菌门(89.56%)和气单胞菌属(82.68%)在其肠道菌群组成中占有绝对优势(P0.05),而另外3组在门分类水平和属分类水平的菌群结构和相对丰度较为相似,优势菌门均为变形菌门、梭杆菌门和厚壁菌门,主要优势菌属为鲸杆菌属、气单胞菌属和乳球菌属;京都基因和基因组百科全书(KEGG)功能预测比较分析发现,各组样品的肠道微生物富集到了多个相同的代谢途径以及部分信号传导、调节和修复机制相关信号通路。本研究结果发现,在稻田和池塘养殖模式下,金边鲤的肠道优势菌群种类、相对丰度以及参与的信号通路与建鲤无显著差异,提示金边鲤与其他鲤鱼一样可适应这两种养殖模式。     

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种间差异,本研究采用基于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(Larimichthys crocea)、黄姑鱼(Nibea albiflora)、鮸状黄姑鱼(Nibea miichthyoides)、鮸鱼(Miichthys miiuy)、眼斑拟石首鱼(Sciaenops ocellatus))的肠道菌群进行了16S rDNA V3-V4区测序。各样本得到unique tags的数目在20351到43347之间,上述5种鱼类分别得到479、626、603、518和556个OTUs(operational taxonomic units),分类注释结果显示,这些OUT隶属33个门273个属。5种石首鱼类肠道内容物和肠道壁的样品均以变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)和厚壁菌门(Firmicutes)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;在属水平上,Bacillus、Photobacterium、Vibrio、Chryseobacterium、Sphingomonas、Pseudomonas等属细菌是5种养殖石首鱼类的主要类别。对养殖石首鱼类的肠道菌群多样性的分析表明,Shannon’s 群落多样性指数：黄姑鱼>鮸状黄姑鱼>眼斑拟石首鱼>鮸鱼>大黄鱼;各种鱼类的肠道内容物菌群的多样性均高于肠道壁;对不同鱼类间的肠道菌群差异性分析显示,大黄鱼与眼斑拟石首鱼之间肠道菌群的相似度要高于黄姑鱼、鮸状黄姑鱼和鮸鱼,而黄姑鱼、鮸状黄姑鱼和鮸鱼之间的相似度较高。综上所述,5种海水养殖石首鱼类肠道菌群中存在有自身特色的核心菌群,肠道菌群结构的差异与种类间的系统进化关系相似,证明肠道菌群结构与宿主遗传因素密切相关。     

池塘和工厂化养殖牙鲆肠道菌群结构的比较分析

为研究池塘和工厂化养殖条件下牙鲆肠道菌群结构差异及其与饵料、水环境、底质等的关系,采用MiSeq高通量测序技术和生物信息学分析手段,构建了牙鲆(Paralichthys olivaceus)肠道、养殖水体、饵料和池塘底泥等7个样品的16s rRNA基因测序文库,分析了不同样品中菌群组成和生物多样性。结果表明：池塘养殖牙鲆肠道（B1）中以厚壁菌门（30.49%）、变形菌门（19.16%）和梭杆菌门（11.11%）为主,其中芽孢杆菌属（27.66%）占绝对优势,弧菌属（0.16%）丰度最小;工厂化养殖牙鲆肠道（B5）中以变形菌门（44.31%）、厚壁菌门（11.57%）和放线菌门（4.79%）为主,其中不动杆菌属（10.37%）丰度最大,弧菌属（4.05%）相对B1中丰度较高。牙鲆肠道优势菌群主要与营养代谢调节相关,同时有益微生物和有害微生物也是肠道菌群的重要组成部分。差异性和系统进化分析表明两种养殖条件下牙鲆肠道菌群结构与饵料中菌群关系密切,此外受养殖水环境中菌群影响较大。研究结果将为今后牙鲆养殖专用高效微生态制剂的研制和养殖环境微生态调控技术构建提供理论依据。     

投喂乙醇假丝酵母对罗非鱼生长、免疫和肠道菌群的影响

为探究乙醇假丝酵母(Candida ethanolica GXU01)在罗非鱼养殖中的益生潜能,为罗非鱼可持续养殖寻找生态友好的饲用添加菌,该研究将乙醇假丝酵母作为饲料添加菌饲喂尼罗罗非鱼(Oreochroms niloticus),通过测定罗非鱼的生长性能、肠道消化酶、血清非特异性免疫指标、肠道微生物群落结构以及用无乳链球菌(Streptococcus agalactiae)对罗非鱼进行攻毒试验,全面评价了乙醇假丝酵母对罗非鱼生长及其免疫力的影响。结果表明,摄食乙醇假丝酵母可以使罗非鱼的生长性能、消化酶活性、血清溶菌酶活性和补体C3含量显著提高(P0.05)。投喂乙醇假丝酵母后,罗非鱼肠道中梭杆菌门、鲸杆菌属(Cetobacterium)和艾克曼菌属(Akkermansia)等有益菌群的丰度显著上调,蓝细菌门大幅减少。攻毒试验中,摄食酵母饲料的罗非鱼成活率增加26.66%。研究表明乙醇假丝酵母对罗非鱼肠道消化能力和免疫抗病能力均有促进作用。     

营养代谢过程中黄条鰤幼鱼消化道菌群的演变趋势

为认识消化道菌群结构在宿主营养代谢过程中的变化规律,并探讨饵料菌群对其的影响,采用16SrDNA高通量测序技术,对黄条鰤(Seriola lalandi)幼鱼一个完整摄食周期内的消化道菌群结构特征进行研究,并解析其与饵料菌群的相关性.结果显示,乳杆菌属(Lactobacillus)、假单胞菌属(Pseudomonas)...     

Digestive enzyme responses of tambaqui (Colossoma macropomum) fed on different levels of protein and lipid

The adaptation of digestive proteases, amylase and lipase was studied in tambaqui fed with 350, 253, 301 and 205 g kg^?1 of crude protein, and 49, 81, 113 and 145 g kg^?1 of lipid, in isocaloric diets. Digestive protease increased when dietary protein increased in stomach, where the highest specific activity was observed. Unspecific protease activity in intestine was very low. Lipase was observed throughout the gastrointestinal tract, and higher activities were observed in the stomach. However, pyloric caecum and the anterior and posterior intestines were the responsive sections to the dietary lipid. Amylase was detected throughout the gastrointestinal tract, but pyloric caecum was the most relevant amylase producer. Positive correlations were observed between anterior intestine lipase versus dietary lipid and pyloric caecum amylase versus dietary protein. Tambaqui is responsive to the food composition adapting the main digestive enzymes to the best profile.     

卵形鲳鲶消化酶活性的研究I．成鱼和幼鱼消化酶活性在不同消化器官中的分布及其比较

比较研究了卯形鲳够（Trachinotus ovatus）成鱼和幼鱼阶段消化酶（蛋白酶、淀粉酶、脂肪酶）在不同消化器官中的活性。结果表明：1）成鱼蛋白酶在不同消化器官中的活性大小依次为胃〉前肠〉中肠〉幽门盲囊〉后肠〉肝；淀粉酶活性为前肠〉后肠〉幽门盲囊〉中肠〉肝〉胃；脂肪酶活性为前肠〉中肠〉后肠〉幽门盲囊〉肝〉胃。2）幼鱼蛋白酶在不同消化器官中的活性大小依次为胃〉肠〉幽门盲囊〉肝；淀粉酶活性为肠〉幽门盲囊〉肝〉胃；脂肪酶活性为肠〉幽门盲囊〉肝〉胃。3）成鱼不同消化器官中蛋白酶和淀粉酶的活性均小于幼鱼，成鱼胃和幽门盲囊的淀粉酶活性与幼鱼的差异显著；幼鱼胃脂肪酶活性大于成鱼，但其他器官的活性均小于成鱼。卵形鲳鳕幼鱼不同消化器官中的3种消化酶活性大小顺序与成鱼基本相似。     

Dietary effects of soybean products on gut microbiota and immunity of aquatic animals: A review

Soybean meal (SBM) is one of the most commonly used vegetable ingredient to replace fish meal in fish diets. However, SBM is limiting in some essential amino acids and contains numerous antinutritional factors and antigens that can affect intestinal microbiota and innate immune system in several finfish species and crustaceans and compromise health. The impact of SBM on health and gut microbiota of aquatic animals is not only affected by SBM in general, but also on the degree of treatment of the meal and exposure. Recently, many studies are actively seeking ways to complement or balance those adverse responses induced by high inclusion of SBM in aquaculture diets. These include advanced processing and mixture of feed with other feed components to balance antinutritional factors. The impact of dietary soybean oil on gut microbiota has also been investigated but to a lesser extent than SBM. As the gastrointestinal tract has been suggested as one of the major routes of infection in finfish species and crustaceans, the effect of soybean products on the gut microbiota is important to investigate. Several studies have focus on supplementation of SBM on the adverse responses of the innate immune system as immunological mechanisms are likely involved in the underlying pathology. However, the precise cause of the inflammatory process has not yet been clarified, even though some investigations have suggested that alcohol‐soluble antinutritional factors, especially soy saponins, are potential causative factors. Possible interactions between soybean products and innate immune system in several finfish species and crustaceans are discussed.     

Intestinal Microbiota in Large Yellow Croaker,Larimichthys crocea,at Different Ages

The polymerase chain reaction–denaturing gradient gel electrophoresis (PCR‐DGGE) of 16S ribosomal RNA gene was used to investigate bacterial communities in the intestines of large yellow croaker at six different ages (12 d, 18 d, 26 d, 40 d, 3 mo, and 1 yr old) as well as within the corresponding feed and culture water. In addition, Illumina Miseq sequencing was utilized to compare intestinal microbiota between 12‐d‐old and 1‐yr‐old individuals. PCR‐DGGE results revealed that the culture water had the highest bacterial diversity, followed by the feed, while the intestines had the lowest diversity. The intestinal microbiota at six ages changed severely; however, the change did not follow any trend. The large yellow croaker intestines harbored specific bacterial communities that differed from those in both feed and water. Illumina Miseq sequencing results revealed that the diversity of intestinal bacteria in 12‐d‐old fish was higher than that in 1‐yr‐old fish, and the bacterial composition differed significantly between them. γ‐Proteobacteria and Pseudoalteromonas supplied the most abundant phylum and genus in the 12‐d‐old fish intestine. However, in the 1‐yr‐old fish intestine, Firmicutes and Clostridium were the most dominant, respectively. The study may contribute to a better understanding of gut microbiota and dynamics of the large yellow croaker and the relationship with their surrounding environment.     

温度和pH值对斜带髭鲷蛋白酶、淀粉酶活性的影响

研究了温度和pH值对斜带髭鲷Hapalogenys nitens蛋白酶、淀粉酶活力的影响。结果表明，斜带髭鲷胃内pH值范围为4.9～5.4；肝胰脏pH值为5.8～6.2；肠道pH值为6.5～6.9。蛋白酶活性随温度的上升而增加，在40℃达最大，40℃以上酶活性随温度的上升而下降。在不同消化器官中，蛋白酶活性大小顺序为：胃〉前肠〉幽门盲囊〉后肠〉肝胰脏。在15～50℃范围内，斜带髭鲷消化道不同部位淀粉酶活性的最适温度均为35℃，淀粉酶活性由高到低顺序为：肝胰脏〉幽门盲囊〉前肠〉后肠〉胃。在pH值为2.2～7.6范围内，胃蛋白酶活性的最适pH值为2.8；在pH值为4.8～8.0范围内，其他消化器官蛋白酶的最适pH值均为7.2；在最适pH值下，各消化器官中的蛋白酶活性由高到低顺序为：前肠〉幽门盲囊〉后肠〉肝胰脏。在pH值为4.8～8.0范围内，胃淀粉酶活性的最适pH值为6.0，肠、肝胰脏与幽门盲囊淀粉酶的最适pH值均为6.8，活性由高到低顺序为：肝胰脏〉幽门盲囊〉前肠〉后肠〉胃。在最适温度和pH值下，蛋白酶活性由高到低顺序为：胃〉前肠〉幽门盲囊〉后肠〉肝胰脏；淀粉酶活性由高到低顺序为：肝胰脏〉幽门盲囊〉前肠〉后肠〉胃。     

围网与普通网箱养殖大黄鱼营养成分的比较与分析

大黄鱼Larimichth ys crocea (Richardson)是我国重要的海洋经济鱼类,传统养殖的大黄鱼肉质已明显不如野生大黄鱼.本实验采用临近海区不同的养殖模式(围网与普通网箱)养殖的大黄鱼肌肉来研究其营养成分(包括常规营养成分和游离氨基酸)的含量与营养评价.结果表明:围网养殖大黄鱼的粗蛋白、氨基酸总量、呈...     

海鳗消化道的显微结构

采用大体解剖和光镜技术研究了海鳗(Muraenesax cinereius)消化道形态学和组织学。海鳗消化道分化为明显的食道、胃和肠。食道皱襞多且粗大，黏膜为复层上皮，部分区域为单层柱状上皮。上皮中含两种类型的杯状细胞，以杯状细胞层次多为显著特征，此外还有嗜酸性细胞。肌层厚。浆膜中纤维发达，伸人肌层并与黏膜下层相连。胃“Y”形，分为贲门部、盲囊部和幽门部，盲囊部发达。胃上皮为单层柱状上皮，贲门部和盲囊部胃腺发达，至幽门部胃腺逐渐消失。肠短，由具微绒毛的单层柱状上皮构成，小肠前段绒毛分支多且相互吻合，毛细血管丰富，平滑肌多。直肠单层柱状上皮与假复层纤毛柱状上皮共存。海鳗消化道组织结构特点反映了其凶猛、食肉、食量大的食性特点。     

Enzyme‐producing bacteria isolated from fish gut: a review

Digestion of food depends on three main factors: (i) the ingested food and the extent to which the food is susceptible to the effects of digestive enzymes, (ii) the activity of the digestive enzymes and (iii) the length of time the food is exposed to the action of the digestive enzymes. Each of these factors is affected by a multitude of secondary factors. The present review highlights the experimental results on the secondary factor, enzymatic activity and possible contribution of the fish gut microbiota in nutrition. It has been suggested that fish gut microbiota might have positive effects to the digestive processes of fish, and these studies have isolated and identified the enzyme‐producing microbiota. In addition to Bacillus genera, Enterobacteriaceae and Acinetobacter, Aeromonas, Flavobacterium, Photobacterium, Pseudomonas, Vibrio, Microbacterium, Micrococcus, Staphylococcus, unidentified anaerobes and yeast are also suggested to be possible contributors. However, in contrast to endothermic animals, it is difficult to conclude the exact contribution of the gastrointestinal microbiota because of the complexity and variable ecology of the digestive tract of different fish species, the presence of stomach and pyloric caeca and the relative intestinal length. The present review will critically evaluate the results to establish whether or not intestinal microbiota do contribute to fish nutrition.