四种不同食性鱼类肠道微生物群落组成及多样性比较分析

本研究旨在探讨食性对鱼类肠道菌群组成和多样性的影响,并预测特定菌群对不同营养素的潜在功能。实验采用高通量16S rRNA基因测序技术,提取获得滇池高背鲫(Carassius auratus)、草鱼(Ctenopharyngodon idellus)、鳜鱼(Siniperca chuatsi)、昆明裂腹鱼(Shizothorax grahami) 4种不同食性鱼类的肠道内容物,12个样品的16S rRNA,构建文库并测序,分析这4种鱼类肠道微生物的菌落组成和多样性。结果显示,鱼类肠道菌群多样性受到食性的显著影响(P<0.05),综合表现为杂食性(滇池高倍鲫) > 草食性(草鱼) > 滤食性(昆明裂腹鱼) > 肉食性(鳜鱼)。4种鱼类具有一些相同的优势菌群：变形菌门(Proteobacteria)和厚壁菌门(Firmicutes)。然而,优势菌群在属水平上存在一定差异,如不动杆菌属(Acinetobacter)为鳜鱼的优势菌群,拟杆菌属(Bacteroides)为草鱼的优势菌群等。功能预测发现,鳜鱼肠道中以革兰氏阴性菌为主;草鱼抗病潜力略高于其他3种鱼类;约氏不动杆菌(A._ johnsonii)、鲁氏不动杆菌(A. lwoffii)和施氏假单胞菌(Pseudomonas stutzeri)可能有助于宿主对蛋白质的消化,而拟杆菌属中的某些菌群可能有助于宿主消化纤维素。综上所述,食性是影响鱼类肠道菌群组成和多样性差异化的主要因素之一,分析食性与肠道优势菌群之间的关联,探讨特异菌群的功能,可为研究鱼类营养代谢的微生物效应奠定理论基础。     

基于16S rRNA高通量测序的江鳕肠道微生物群落结构研究

为探究江鳕(Lota lota)肠道菌群结构特征,采用MiSeq 16S rRNA高通量测序技术对3龄、4龄、5龄野生江鳕的雌、雄样本进行了微生物测序和分析。结果显示,3个年龄组江鳕的肠道菌群丰度及多样性差异不显著(P＞0.05),同一年龄雌、雄江鳕间的肠道菌群丰度及多样性差异不显著(P＞0.05)。江鳕肠道内容物的优势菌门为变形菌门和厚壁菌门,与鱼类肠道中最普遍和共存的细菌类群相同。Mycoplasma(支原体属)存在于所有样品中,且为优势菌群,其功能有待进一步研究。     

Effects of live and artificial feeds on the growth,digestion, immunity and intestinal microflora of mandarin fish hybrid (Siniperca chuatsi ♀ × Siniperca scherzeri ♂)

How to acclimate mandarin fish to eat artificial feeds has been always a challenge for researchers. The mandarin fish after hybridization (Siniperca chuatsi ♀ × Siniperca scherzeri ♂) could be fed artificial feeds which solved the problem to some extent. However, the growth performance, digestibility, immunity and intestinal microflora of mandarin fish hybrid fed artificial feeds need further study. One hundred and twenty fish of similar size (average weight, 19.5 ± 0.9 g) were randomly stocked into six 250‐L aquariums and separately fed live baits (the control) or artificial feeds in triplicate for 70 days. The weight gain and special growth rate of fish fed artificial feeds were significantly lower than those of fish fed live baits (P < 0.05). The protease activities of stomach, liver and intestine in fish fed live baits were all significantly higher than those in fish fed artificial feeds. The activities of catalase and lysozyme, the content of glutathione in serum of fish fed live baits were all significantly higher than those in fish fed artificial feeds. However, the content of malondialdehyde in liver of fish fed artificial feeds was significantly higher than that in fish fed live baits. The dominant bacteria in both groups were Proteobacteria, Bacteroidetes, Planctomycetes, Cyanobacteria, Verrucomicrobia. However, live baits greatly affected the amount of beneficial and harmful bacteria of intestine in mandarin fish hybrid and broke the balance of intestinal flora.     

应用高通量测序技术分析大菱鲆幼鱼肠道及其养殖环境的微生物群落结构

采用基于Illumina测序平台的高通量测序技术,对大菱鲆(Scophthalmus maximus)幼鱼肠道及其养殖水体、生物饵料中细菌种类及丰度进行研究。测序结果显示,养殖水体、生物饵料和大菱鲆幼鱼肠道等19个样品共获得有效序列547621条,可聚类于3771个可分类操作单元(OTUs),归属于养殖水体、生物饵料、健康幼鱼和发病幼鱼的操作分类单元(OTU)个数分别为3038、1090、87和777,其中,健康幼鱼与生物饵料、健康幼鱼与养殖水体特有的OTU个数分别为57和0,发病幼鱼与生物饵料、发病幼鱼与养殖水体特有的OTU个数分别为481和31。表明幼鱼肠道微生物多样性与生物饵料密切相关。根据细菌注释结果,拟杆菌门(Bacteroidetes)、厚壁菌门(Firmicutes)和变形菌门(Proteobacteria)在大菱鲆幼鱼肠道中占优势地位,其中,健康幼鱼肠道微生物共聚类为8个门,发病幼鱼的肠道微生物可聚类为19个门。与健康幼鱼相比,发病幼鱼肠道门水平上的3种主要优势菌群落结构出现失衡。此外,对各样品中丰度最高的100位OTU分析显示,幼鱼肠道优势菌种类与生物饵料中的优势菌种类密切相关,而每个发病幼鱼肠道优势菌种类具有一定的独立性。本研究旨在为大菱鲆健康养殖和微生态调控提供实验依据。     

Microflora of Arctic charr, Salvelinus alpinus (L.): gastrointestinal microflora of free-living fish and effect of diet and salinity on intestinal microflora

Abstract. The adherent aerobic bacterial flora present in the gastrointestinal tract and faeces of free-living Arctic charr, Salvelinus alpinus (L.), from Lake Takvatn, Northern Norway, were identified both qualitatively and quantitatively. Approximately 10⁵ bacteria g⁻¹ were found in both the small and large intestines. The predominant bacterial species were identified as Aeromonas , Enterobacteriaceae, Micrococcus and Lactobacillus. Other microorganisms isolated included Acinetobacter, Cytophaga, Flavobacterium, Moraxella, Pseudomonas, Vibrio , Coryneforms and Streptococcus. The intestinal microflora of free-living fish was dominated by Aeromonas and Lactobacillus , but the intestinal bacterial flora of wild fish transferred to hatchery was affected by feeding them either a capelin roe diet or a commercial feed in fresh and sea water. Approximately 55% of the bacterial flora in intestinal contents from fish fed the capelin roe diet was Enterobacteriaceae when the fish were held in fresh and sea water. However, when the wild-caught charr were fed a commercial diet in fresh water, Aeromonas and Pseudomonas dominated in faeces, while Vibrio and Pseudomonas were predominant in the diet group held in sea water.     

The autochthonous microbiota of the freshwater omnivores jundiá (Rhamdia quelen) and tilapia (Oreochromis niloticus) and the effect of dietary carbohydrates

Previous studies have shown that the gut microbiota of fish differs depending on host feeding habits and these populations may also be influenced by dietary ingredients. In this study, the bacterial populations of the intestinal tract of the opportunistic omnivore jundiá Rhamdia quelen and the typical omnivore tilapia Oreochromis niloticus were investigated in two experiments. In experiment I, the levels of amylolytic, cellulolytic, lipolytic, proteolytic and total culturable bacteria were compared in the proximal, mid and distal intestine using selective agar. Higher levels of amylolytic, cellulolytic, lipolytic, proteolytic and total culturable bacteria were observed in the tilapia than jundiá, in all intestinal regions. Jundiá contained higher levels of proteolytic bacteria and lipid digesting bacteria in the distal intestinal portion as compared with the mid intestine; both fish species also presented more amylolytic bacteria in the distal intestine. In experiment II, the amylolytic intestinal microbiota between the two species was compared after administration of diets containing different carbohydrate sources. Jundiá fed broken rice presented higher total culturable bacterial levels; however, dietary cassava bagasse and ground corn significantly elevated the population of amylolytic bacteria in tilapia (P > 0.05). PCR‐DGGE was also used to assess the bacterial communities in experiment II. A Cetobacterium spp. was detected in jundiá fed diets containing broken rice, and tilapia fed cassava bagasse, dextrin, broken rice and ground corn. Microbial differentiation was further demonstrated between jundiá and tilapia, because an uncultured bacterium was unique in tilapia and an uncultured spirochete was observed only in jundiá; the presence of these bacterial species was also influenced by dietary carbohydrate sources.     

饲料中添加大豆皂甙对大菱鲆幼鱼生长和肠道健康的影响

为研究大豆皂甙对大菱鲆幼鱼生长性能、消化酶活性、肠道组织结构完整性和肠道菌群结构的影响,在以鱼粉为蛋白源的基础饲料中分别添加0%和0.3%的大豆皂甙,配制成鱼粉组和大豆皂甙组2种等氮等脂的实验饲料来投喂体质量为(4.63±0.01) g的大菱鲆进行12周的摄食生长实验。结果显示,饲料中添加0.3%的大豆皂甙对大菱鲆的生长性能没有产生显著影响,但显著降低了胃蛋白酶及肠淀粉酶活性;2组实验中大菱鲆肠道组织形态无明显差异,但大豆皂甙组肠道紧密连接蛋白的基因表达量显著降低。肠道菌群分析结果显示,大菱鲆肠道中相对丰度最高的门和属分别为变形菌门和盐单胞菌属。LEfSe和MetaStat分析显示,饲料中添加大豆皂甙后显著提高了大菱鲆肠道内优势菌(变形菌门及希瓦氏菌属),皂甙水解相关的肠道微生物(鞘脂单胞菌属、普氏菌属、栖瘤胃普雷沃菌以及普通拟杆菌)及潜在致病菌(莫氏杆菌属和发光杆菌属)的相对丰度,同时显著降低了Caenimonas、Niastella和条件致病菌罗尔斯通菌属的相对丰度。研究表明,0.3%大豆皂甙抑制了大菱鲆消化酶活性及肠道紧密连接蛋白的基因表达,且引起了大菱鲆肠道菌群结构的显著改变。因此,大豆皂甙对鱼类肠道健康尤其是肠道菌群的影响不容忽视,值得进一步研究。     

Bacterial community composition shifts in sediments influenced by fish feeds

This study investigated the influence of fish feed deposition on the microbial community of sediments in a coastal lake. Microcosms were designed to simulate the addition of fish feeds to the sediment, and physicochemical factors as well as composition of microbial assemblages were analysed. Although total organic carbon and total organic nitrogen did not significantly increase, redox potential and total sulphides showed a transition of sediment environments into anaerobic condition due to the addition of fish feeds. The bacterial community composition shifted with fish feed deposition as revealed by the band profiles of denaturing gradient gel electrophoresis, Sørensen's similarity indices and cell numbers of sulphate‐reducing bacteria. Occurrence of anaerobic bacteria (sulphate and nitrate reducers) and disappearance of strictly aerobic bacteria were observed with fish feed inputs. The results clarify the succession of the microbial flora and suggest negative impact of uneaten fish feeds on the microbial community in sediment and resultant environmental deterioration of fish‐farming areas.     

Soybean meal alters autochthonous microbial populations, microvilli morphology and compromises intestinal enterocyte integrity of rainbow trout, Oncorhynchus mykiss (Walbaum)

Rainbow trout were fed either a diet containing fishmeal (FM) as the crude protein source or a diet containing 50% replacement with soybean meal (SBM) for 16 weeks. An enteritis-like effect was observed in the SBM group; villi, enterocytes and microvilli were noticeably damaged compared with the FM group. The posterior intestine microvilli of SBM-fed fish were significantly shorter and the anterior intestine microvilli significantly less dense than the FM-fed fish. Electron microscopy confirmed the presence of autochthonous bacterial populations associated with microvilli of both fish groups. Reduced density of microvilli consequently led to increased exposure of enterocyte tight junctions, which combined with necrotic enterocytes is likely to diminish the protective barrier of the intestinal epithelium. No significant differences in total viable counts of culturable microbial populations were found between the groups in any of the intestinal regions. A total of 1500 isolates were tentatively placed into groups or genera, according to standard methods. Subsequent partial 16S rRNA sequencing revealed species that have not been identified from the rainbow trout intestine previously. Compared with the FM group levels of Psychrobacter spp. and yeast were considerably higher in the SBM group; a reduction of Aeromonas spp. was also observed.     

The isolation of intestinal microflora of farmed red seabream (Pagrus major) and black seabream (Acanthopagrus schlegeli) at larval and juvenile stages

The aerobic bacterial flora in the intestine of farmed red seabream and black seabream was investigated at their larval and juvenile stages in relation to the microflora of ambient water and diets. The total bacterial number in the intestine was 7.4×10⁴ and 3.4×10⁴ colony-forming units (CFU)/fish for red seabream and black seabream, respectively. Among the intestinal flora, Vibrio (ca. 45%) and Pseudomonas (30%) were the most dominant bacteria.The total bacterial counts were 3.1×10⁴ CFU/ml for rearing water, 2.1×10⁷ CFU/g for live diets (rotifer and brine shrimp) and 1.2×10⁴ CFU/g for artificial diets. Among the water bacteria, Pseudomonas (22%) and Moraxella (29%) constituted dominant groups, and in the live diets Pseudomonas (48%) was predominant. The incidence of Vibrio in waters and live diets was 7% and 11%, respectively.     

A study on bacteria associated with the intestinal tract of farmed yellow seahorse,Hippocampus kuda (Bleeker, 1852): characterization and extracellular enzymes

The microenvironment of bacteria associated with the gastrointestinal tract of an animal influences the host in many ways, including the metabolism of several nutrients. Isolation, molecular characterization and enzymatic activities of culturable bacteria associated with the gastrointestinal tract of hatchery‐reared oceanic yellow seahorse, Hippocampus kuda, were investigated in the present study. 16S rRNA sequencing of bacterial isolates yielded 10 different bacterial genera belonging to two major groups: proteobacteria (62.9%) and firmicutes (37.03%). The predominant microbial flora belonged to the genera Vibrio spp., Enterovibrio sp. and Bacillus spp. Burkholderia cenocepacia, hitherto unreported from the gastrointestinal tract of marine fish, was retrieved from the seahorse gut, albeit in small numbers. Enzymatic studies indicated that the bacterial isolates possess the ability to degrade lipids, cellulose, xylan, starch and proteins. Lipase activity was exhibited by a majority of the isolates (70.4%), indicating that the bacterial flora associated with the intestinal tract of seahorses is capable of digesting foods rich in lipids. The possible implications for the role of these bacteria in the digestion and physiological processes are discussed. To our knowledge, this is the first time that the characterization and enzymatic activities of bacteria associated with the intestinal tract of farmed seahorses have been reported.     

两种疾病发生对养殖半滑舌鳎肠道菌群结构的影响分析

为研究疾病发生情况下鱼类肠道菌群的结构变化,运用高通量测序方法分别对感染腹水病和皮肤溃疡病的工厂化养殖半滑舌鳎病鱼及同一养殖系统中健康鱼的肠道菌群结构进行了对比分析。结果发现,养殖半滑舌鳎肠道中的细菌种类要明显少于环境中的细菌种类,仅为养殖池进水和颗粒饲料中细菌种类总数的14.3%~44.7%。在疾病发生后,病鱼肠道中的细菌种类数量仅是同一养殖系统中健康鱼肠道细菌种类数量的45.8%和64.5%,病鱼肠道中细菌多样性下降非常明显。进一步分析肠道菌群结构的组成发现,虽然发病鱼和健康鱼肠道中超过60%的细菌种类不相同,但优势菌群的结构组成差异不明显,丰度最高的前10种细菌种类基本相同,其比例超过肠道相对总菌量的80%。不同疾病的发生对半滑舌鳎肠道菌群结构的影响也不同,腹水病会造成肠道中优势菌株的种类和相对丰度都发生比较明显的改变,而皮肤溃疡病发生前后肠道菌群结构组成几乎没有变化。研究表明,养殖半滑舌鳎的肠道菌群结构相对比较保守,而且并不是所有的疾病种类都会引起肠道菌群结构发生改变。     

大菱鲆仔稚鱼发育早期肠道菌群结构形成的影响因素

为研究鱼类发育早期肠道菌群结构的演变过程及影响因素,运用高通量测序技术,分析了处于不同发育阶段的大菱鲆(Scophthalmus maximus)仔稚鱼肠道、受精卵、不同类型的饵料和水源中的菌群结构,以及它们之间的相关性。结果显示,以不同的OTU(Operational Taxonomic Units,可操作分类单元)作为分类依据,发现大菱鲆仔稚鱼的肠道菌群结构在开口摄食后不久已趋于稳定,其优势菌与受精卵所携带的细菌关联较大。并且在大菱鲆仔稚鱼不同的发育时期,这一菌群的结构非常稳固,几乎不受水和饵料中优势细菌的影响而发生改变。乳球菌属的Lactococcus piscium菌株一直是大菱鲆仔稚鱼肠道中的优势菌种,在不同发育时期的优势度高达45%~65%。本研究还发现,大菱鲆仔稚鱼肠道可能对定植的菌种具有选择性,一些水环境和饵料中的非优势菌,如Streptococcus sp.,Pseudomonas sp.,Carnobacterium sp.等细菌也会定植于肠道,成为大菱鲆肠道中的次优势菌。     

育肥饲料中虾青素含量对雄性中华绒螯蟹肠道和鳃部可培养优势细菌数量和组成的影响

在育肥饲料中添加虾青素会影响中华绒螫蟹肠道及鳃内的可培养优势菌群以及机体的免疫力,本实验旨在探讨饲料中虾青素含量及养殖水体对其肠道和鳃部菌群的影响。采用不同虾青素含量的饲料(0.00、26.60、41.62、81.37和75.35 mg/kg,分别对应饲料1#~5#)对雄性中华绒螫蟹进行育肥70 d后,利用基础培养基和选择性培养基对其肠道、鳃及养殖水体中的细菌进行传统分离和纯化,所得菌株进行16S rRNA测序,再进行同源性分析后做系统进化树。结果发现,在分离获得的106株细菌(登录号:KU570293~KU570368,KU570370,KU570372~KU570383,KU601302~KU6013 16,KU720553)中,92株为优势菌株,其中,肠道、鳃部和水体各29、32和31株。肠道中的可培养优势细菌属于柠檬酸杆菌属、假单胞菌属和气单胞菌属;而鳃中可培养优势细菌属于柠檬酸杆菌属、芽孢杆菌属、假单胞菌属和气单胞菌属;养殖水体中可培养优势细菌属于芽孢杆菌属、气单胞菌属、柠檬酸杆菌属、假单胞菌属和黄杆菌属。饲料2#组肠道中可培养细菌总数最高(1.06×10~8cfu/g);饲料5#肠道中的潜在致病菌数量最低,但其可培养细菌总数显著高于其他饲料组;饲料3#组肠道和鳃中潜在致病菌数量相对较高。研究表明,饲料中添加不同含量的虾青素能够显著影响雄性中华绒螫蟹肠道和鳃中的菌群构成,但对水体中可培养细菌数量无显著影响。本研究首次对投喂不同含量虾青素饲料的育肥期雄性中华绒螫蟹肠道、鳃及养殖水体可培养的优势细菌数量和组成进行分析,探究了饲料中虾青素含量以及养殖水体与蟹肠道内可培养细菌之间的联系,为中华绒螫蟹营养免疫和菌群调控提供了理论基础。     

Clinical and aetiological aspects of a summer enteritic syndrome associated with the sporulating segmented filamentous bacterium 'Candidatus Arthromitus' in farmed rainbow trout, Oncorhynchus mykiss (Walbaum)

An enteritic syndrome affecting farmed rainbow trout and occurring predominantly in summer has recently been described and related to the massive accumulation of a segmented filamentous bacterium (SFB), ‘Candidatus Arthromitus’, in the digestive tract of fish. Details of the clinical manifestations, the characteristics of the bacterium and the possible aetiology of the disease are presented in this paper. No other bacterial pathogen than ‘Candidatus Arthromitus’ was characterized in trout undergoing the enteritic syndrome. From clinical and histopathological observations, a toxin or toxic product accumulation was suspected in affected trout, and could account for the massive destruction of the intestinal mucosa. However, the origin and aetiological role of the SFB could not be clearly elucidated, although most of the filaments appeared to beviable and to produce and release strings of endospores in the lumen of the gut. The organism could not be cultured in the conditions tested, shared several morphological and structural characteristics with related bacteria described in the intestinal microflora of different vertebrate species, but no attachment structure was definitively recognized. All attempts to detect similar SFB in the fish diet orin the environment of affected fish farms were unsuccessful. It is unclear whether this organism represents a normal and not previously detected inhabitant of the intestine of trout stressed after environmental perturbation, or whether it results directly from external sources of contamination.     

Survival,persistence and proliferation of Vibrio anguillarum in juvenile turbot,Scophthalmus maximus (L.), intestine and faeces

The aim of this study was to determine whether orally administered V. anguillarum cells could survive passage through the intestinal tract of feeding turbot, and thereafter, proliferate in the released faeces. In addition, the growth of the pathogen in turbot faeces in the presence of a Carnobacterium sp. with inhibitory effects against a number of bacterial fish pathogens was studied. It was found that V. anguillarum cells survived the acidic environment of the stomach for several hours, persisted in the intestine and readily proliferated in the released faeces. The antagonistic Carnobacterium sp. inhibited the growth of V. anguillarum during co-culture in turbot faecal extracts. From the results, it was concluded that the turbot intestinal tract and faeces can serve as an enrichment site for V. anguillarum, and the use of intestinal bacteria with antagonistic activity against vibrios may be used to reduce the load of fish pathogenic vibrios in turbot hatcheries.     

养殖刺参早期发育阶段体内可培养细菌的菌群特征及其与环境菌群相关性分析

采用传统细菌培养方法,对养殖刺参(Apostichopus japonicus)早期发育各阶段幼体体内及环境(投入饵料及培育用水)菌群的组成与结构展开研究,对分离的优势细菌进行分子鉴定,在此基础上,进行了刺参幼体体内菌群结构与环境菌群结构相关性分析。幼体各发育期的细菌培养结果显示,在幼体开口前的各发育时期(性腺、卵、受精卵、原肠胚)均无可培养细菌,在投饵以后,耳状幼体、樽形幼体体内可分离到可培养细菌,幼体发育到稚参以后,消化道可培养细菌总数急剧增加,并在4月龄时达到108 CFU/g数量级。在幼体体内可培养细菌中,弧菌(Vibrio)占比为2.2%~77.3%。对环境菌群的细菌培养结果显示,培育用水中细菌含量变化不显著,随着幼体发育期饵料的转变,不同时期饵料中细菌含量差异显著。整个养殖系统中共分离到65株优势细菌,16S rDNA鉴定结果显示,所分离的65株优势菌鉴定为14个属43种细菌。相关性分析结果显示,随着幼体的发育,生物饵料中的细菌对消化道中的菌群结构影响越来越大。本研究结果为解析刺参消化道菌群的形成过程和演替规律以及养殖用益生菌的筛选与应用奠定了基础。     

Evidence of enhanced bacterial invasion during Diplostomum spathaceum infection in European grayling, Thymallus thymallus (L.)

Farmed grayling, Thymallus thymallus (L.), are susceptible to atypical Aeromonas salmonicida (aAS) infections. Interactions between bacteria and parasites were studied using grayling subjected to concomitant exposure to aAS bacteria and the digenean parasite Diplostomum spathaceum. Atypical AS was detected from fish by a combination of bacterial cultivation and polymerase chain reaction techniques. A detection level of 17 aAS cells per 100 mg intestine tissue sample was obtained. Concomitant bacterial exposure did not enhance the severity of grayling eye rupture and nuclear extrusion induced by D. spathaceum, but D. spathaceum invasion into grayling increased the proportion of fish carrying aAS in their heart tissue. However, the number of aAS cells detected in heart tissue was low. Atypical AS did not cause acute disease or mortality during 15 days post-exposure. There was a higher prevalence of aAS in grayling heart samples than in intestinal samples, indicating that the intestine is not favoured by aAS. We suggest that heart tissue would be a good organ from which to isolate aAS when tracing latent carrier fish. We conclude that penetrating diplostomids can enhance bacterial infections in fish and that diplostomids can cause serious eye ruptures in grayling.     

Effects of sublethal concentrations of lignosulphonates on growth,intestinal flora and some digestive enzymes of rainbow trout (Salmo gairdneri)

Young rainbow trout (Salmo gairdneri) were exposed to lignosulphonates (LS) at concentrations of 0, 40, 80, 160, 320, 640, 1 280 and 1 920 ppm for 35 or 60 days. At concentrations of 160 ppm LS and higher the growth rates were slower. The higher concentrations had the most retarding effect on growth, but a clear general relationship between LS concentration and growth retardation was not observed.The bacterial flora in the digestive tract of the fish was examined. The predominant micro-organisms were flavobacteria, bacilli, streptococci and yeasts (Cryptococcus spp.), which were also isolated from the diet. There were about 10 000 viable aerobic and 1 000 anaerobic bacteria per gramme of intestinal contents. There was no significant difference in quantitative or qualitative composition of the intestinal flora of the different groups.The following groups of digestive enzymes were studied: proteinases, amylases, lipases and deoxyribonucleases. The activities of proteinases and nucleases were significantly impaired in fish exposed to concentrations of 1 280 ppm LS and higher, and those of amylases at concentrations of 320 ppm LS and higher. A possible connection between the reduced growth rates and depressed activities of the digestive enzymes is discussed, but no firm conclusion regarding the mechanism by which LS effects fish growth can be made on the basis of the present study.     

野生与养殖黄鳍鲷消化道中粘液细胞的类型及分布

采用常规石蜡组织切片及AB-PAS的染色方法对野生和养殖黄鳍鲷（Sparus latus）消化道中粘液细胞的类型及分布情况进行了比较观察研究。黄鳍鲷粘液细胞在消化道各部位均有分布,不同部位粘液细胞的类型和分布均有差异。食道中以Ⅰ、Ⅱ型粘液细胞为主;贲门部和胃体部只有Ⅰ、Ⅱ型粘液细胞分布,幽门部只有Ⅰ型粘液细胞;幽门盲囊、肠道及直肠都是Ⅱ型粘液细胞最多。野生与养殖黄鳍鲷粘液细胞的区别在于消化道的相同部位养殖鱼比野生鱼粘液细胞数量更多。根据研究结果推测粘液细胞的类型和分布与鱼的生活环境及食物相关,也可能与消化道中各种菌群的分布有关。