鱼类肠道菌群的研究概况

鱼类肠道存在着正常的细菌群落,这些微生物群为宿主创造生存的微环境,同时宿主也为它们提供生长繁衍的条件,两者相互依赖、相互制约,形成了统一的整体。综述了鱼类肠道菌群的研究意义、肠道菌群的形成、肠道菌群的数量和组成、肠道菌群的作用。肠道菌群的作用主要包括辅助消化作用、肠道菌群的变化和免疫机能的相关性、对外来菌群和寄生虫的作用、提供营养物质等。     

鱼类肠道菌群与免疫调节研究进展

介绍了鱼类肠道菌群的形成和种类以及对鱼类机体免疫调节的作用,重点介绍了鱼类肠道菌群与免疫调节之间的关系,包括肠道菌群对免疫机能的影响和免疫调节剂对肠道菌群的影响两方面。     

鱼类肠道菌群影响因子研究进展

肠道菌群在维持肠道健康、促进肠道发育、抵抗病原入侵、调节机体能量吸收和脂质代谢过程中均发挥重要作用。在鱼类学研究中,由于种类繁多、食性差异大、生存环境复杂多变,导致鱼类肠道菌群方面的研究面临巨大挑战。本文在总结常见鱼类肠道微生物组成的基础上,着重介绍了鱼类饵料组成、水环境因子、物种、基因型、发育阶段、养殖模式及投喂策略对鱼类肠道菌群影响的相关研究进展,并对目前研究中存在的问题进行了剖析,以期为鱼类肠道菌群研究提供一定的参考依据。     

鱼类肠道菌群的研究现状

本文阐述了鱼类肠道菌群的形成、数量、组成、分布，重点分析了鱼类肠道菌群对鱼体所起的作用。     

鱼类肠道菌群与机体脂质代谢关系研究进展

鱼类肠道内存在着大量的微生物类群,其在宿主生长发育、代谢及免疫调控过程中扮演着重要的角色。大量研究显示肠道菌群与宿主脂代谢关系密切,能够通过调节肠道短链脂肪酸(short-chain fatty acids,SCFAs)、内毒素(lipopoly saccharide, LPS)、胆汁酸、氧化三甲胺等菌群代谢产物以及肠上皮细胞的通透性,影响宿主脂质代谢。本文对国内外鱼类肠道菌群及其与机体脂质代谢作用关系进行梳理,综合报道了鱼类肠道菌群的组成、脂类营养对鱼类肠道菌群的影响、鱼类肠道菌群与机体脂质代谢的关系及基于肠道菌群调控鱼类脂质代谢的策略。在鱼类肠道中,菌群种类及结构的变化或可作为鱼类脂代谢紊乱的早期诊断标志。在此基础上,基于肠道菌群稳态维持而采取调控手段,如合理应用益生菌、益生元等,或将为鱼类等水产动物脂质代谢紊乱防控提供新的方法。     

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。     

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。     

鱼类肠道微生物总DNA的提取

尝试提取鲫(Carassius auratus)肠道菌群总DNA,为研究鱼类肠道菌群结构提供依据。以鲫肠道内容物为样本,用PBS多次洗涤,离心样品,沉淀菌体。使用试剂盒法提取肠道菌群总DNA,电泳结果显示,样品DNA条带明亮,无降解现象,可用于后续分子生物学试验研究;通过设计的细菌通用引物,对其16S rDNA基因进行PCR扩增,得到较清晰的图谱,条带整齐;表明采用该方法提取鱼类肠道微生物群落的DNA较为简单、准确、可行。     

鱼类消化道乳酸菌的分布及功能研究进展

乳酸菌是鱼消化道固有菌群的组成部分,能定植于鱼类消化道,拮抗革兰氏阴性致病菌,维持肠道正常的微生态平衡.鱼消化道中比较常见的乳酸菌种类有肉杆菌、乳酸杆菌等.综述了乳酸菌在不同生长阶段鱼消化道的分布、鱼类消化道乳酸菌分布的影响因素和鱼类消化道乳酸菌的功能.     

达氏鳇和施氏鲟生长差异群体肠道菌群特征

同塘生长差异常常导致鲟养殖产量受损, 而肠道菌群是影响鱼类生长性能的关键因素之一。为揭示肠道菌群与鲟科鱼类个体生长差异之间的关系, 本研究对同批次繁育、同条件养殖的生长速率差异大于体重 50%的达氏鳇 (Huso dauricus)和施氏鲟(Acipenser schrencki)群体进行了肠道菌群特征研究。结果表明, 达氏鳇和施氏鲟肠道菌群多样性和组成在种属间及生长差异群体间均具有明显差异。其中, 生长快速达氏鳇群体(LH)肠道优势菌属为鞘氨醇单胞菌属(Sphingomonas, 67.0%), 生长慢速达氏鳇群体(SH)肠道优势菌属为鞘氨醇单胞菌属(29.5%)和狭义梭菌属 1 (Clostridium sensu stricto 1, 54.2%); 而生长快速施氏鲟群体(LA)肠道优势菌属为鞘氨醇单胞菌属(33.5%)和鲸杆菌属(Cetobacterium, 38.1%), 生长中速施氏鲟群体(MA)肠道优势菌属为鞘氨醇单胞菌属(42.6%)、狭义梭菌属 1 (14.3%)和鲸杆菌属(33.0%)。鞘氨醇单胞菌属和梭菌科(Clostridiaceae)细菌是不同生长速率鲟肠道中的主要差异类群。综上可知, 鲟科鱼类肠道菌群的多样性和组成具有种属差异性和群体差异性, 鞘氨醇单胞菌属和梭菌科细菌可能是影响鲟科鱼类生长速率的关键细菌类群。     

Association between the interannual variation in the oceanic environment and catch rates of bigeye tuna (Thunnus obesus) in the Atlantic Ocean

The environmental processes associated with variability in the catch rates of bigeye tuna in the Atlantic Ocean are largely unexplored. This study used generalized additive models (GAMs) fitted to Taiwanese longline fishery data from 1990 to 2009 and investigated the association between environmental variables and catch rates to identify the processes influencing bigeye tuna distribution in the Atlantic Ocean. The present findings reveal that the year (temporal factor), latitude and longitude (spatial factors), and major regular longline target species of albacore catches are significant for the standardization of bigeye tuna catch rates in the Atlantic Ocean. The standardized catch rates and distribution of bigeye tuna were found to be related to environmental and climatic variation. The model selection processes showed that the selected GAMs explained 70% of the cumulative deviance in the entire Atlantic Ocean. Regarding environmental factors, the depth of the 20 degree isotherm (D20) substantially contributed to the explained deviance; other important factors were sea surface temperature (SST) and sea surface height deviation (SSHD). The potential fishing grounds were observed with SSTs of 22–28°C, a D20 shallower than 150 m and negative SSHDs in the Atlantic Ocean. The higher predicted catch rates were increased in the positive northern tropical Atlantic and negative North Atlantic Oscillation events with a higher SST and shallow D20, suggesting that climatic oscillations affect the population abundance and distribution of bigeye tuna.     

Growth performance,digestive enzyme activity and immune response of Japanese sea bass,Lateolabrax japonicus fed with fructooligosaccharide

In this experiment, a feeding trial was performed to determine the effects of fructooligosaccharide (FOS) on growth performance, digestive enzyme activity and immune response of Japanese sea bass, Lateolabrax japonicus juveniles (initial weight 38.3 ± 0.5 g), and the fish were examined following feeding with six levels of FOS (0, 0.5, 1, 2, 4 and 6 g/kg) for 28 days. Significant enhancement of weight gain (WG) and specific growth rate (SGR) was found in fish fed 1 g/kg FOS incorporated diets (p < .05), while the feed conversion ratio (FCR) in the 1, 2 g/kg FOS groups reduced significantly compared with the control (p < .05). Besides, the crude lipid in the 4, 6 g/kg FOS groups increased significantly compared with the control (p < .05). On the other hand, the erepsin and lipase activities significantly elevated in intestine of fish fed 2 g/kg FOS (p < .05) and the lysozyme activity in serum of fish fed 2 g/kg FOS were significantly higher than that in the control (p < .05). Moreover, the alkaline phosphatase activities in serum of fish fed 0.5, 1, 2 g/kg FOS were significantly higher than in control (p < .05). Regression analysis showed that the relationships between dietary FOS levels and either SGR, FCR, erepsin or lysozyme activities were best expressed by regression equations, and the optimal inclusion levels are 1.37, 1.80, 3.06, 3.11, 1.93 and 1.80 g/kg for SGR, FCR, erepsin, lipase, lysozyme and total superoxide dismutase activities, respectively. Overall, this study revealed that FOS incorporated diets could beneficial for L. japonicus culture in terms of increasing the growth, digestion and immune activities. Under the present experimental condition, the optimal supplementary level of FOS in the diet of L. japonicus is 1–3 g/kg.     

Protein and amino acid composition from the mantle of juvenile O ctopus vulgaris exposed to prolonged starvation

Protein and amino acid composition of the mantle of juvenile O ctopus vulgaris (Cuvier, 1797) during fasting for 27 days were determined. Average protein content of octopus mantle was of 711.19 ± 46.80 g kg^?1 DW, and it decreased with increasing fasting days. The non‐essential amino acids content was higher (486.18 ± 11.08 g kg^?1 protein) than essential amino acids (425.82 ± 9.15 g kg^?1 protein) at the start of the experiment (unstarved animals). The results suggest that the amino acid profile of the mantle where the most abundant amino acids are Arg, His, Lys, Gly, Leu and Pro could indicate a prolonged fasting condition (>20 days) or poor nutrition of O . vulgaris. This study supports the idea of using mantle for metabolic needs of starved O . vulgaris suggesting that the degradation pathway of amino acids to pyruvate and tricarboxylic acid cycle intermediates was favoured contrary to the degradation pathway of ketogenic amino acids. Special considerations should be taken concerning Thr, Ile, Ser, Ala, Asx (Asp, Asn), Glx (Glu, Gln) (because of their fast intake) and Lys and His (due to their stable contents) during a prolonged period of fasting.     

Involvement of gonadal steroids in final oocyte maturation of white perch (Morone americana) and white bass (M. chrysops): in vivo and in vitro studies

Plasma estradiol-17 (E₂), testosterone (T), 17,20-dihydroxy-4-pregnen-3-one (DHP) and 17,20,21-tri-hydroxy-4-pregnen-3-one (20-S) levels were measured by radioimmunoassay (RIA) in white perch (Morone americana) and white bass (M. chrysops) that were induced to undergo final oocyte maturation (FOM) with human chorionic gonadotropin (hCG). Plasma DHP levels increased in females of both species in association with oocyte germinal vesicle migration (GVM) and germinal vesicle breakdown (GVBD) and decreased thereafter. Plasma 20-S levels also increased with oocyte GVM in white bass, but were several-fold lower than DHP levels. Circulating E₂ and T levels were greatest during GVM and GVBD in both species and decreased to low levels during oocyte hydration and ovulation. Follicles from white perch and white bass which received a priming injection of hCG in vivo, produced both DHP and 20-S in vitro after exposure to hCG and their oocytes underwent GVBD. Ovarian incubates from unprimed fish of either species produced only E₂ and T and their oocytes did not complete GVBD. Oocytes from unprimed bass, but not perch, matured when follicles were exposed to hCG in vitro. Both trilostane and cycloheximide blocked in vitro production of DHP and 20-S and oocyte GVBD by white perch follices. DHP and 20-S were equipotent inducers of FOM in the GVBD bioassay. None of several other structurally-related steroids tested were effective within a physiological range of concentrations. These results indicate a role for DHP and 20-S in the control of FOM in white perch and white bass.     

Cardiac,ventilatory and metabolic responses of two ecologically dissimilar species of fish to waterborne cyanide

Changes in heart rate, ventilatory activity and oxygen consumption were determined in trout (Salmo gairdneri) and brown bullhead catfish (Ictalurus nebulosus) during exposure to a steadily increasing concentration of waterborne cyanide selected to produce death in 8–9 hours for each species. The lethal cyanide concentration for the bullheads was an order of magnitude higher than for trout. Trout developed an immediate and gradually increasing bradycardia throughout the exposure period. Cyanide produced tachycardia in the bullhead followed by a gradual onset of bradycardia as the concentration of cyanide was raised. Pericardial injection of atropine (a muscarinic cholinergic antagonist) indicated that bradycardia in the trout was due initially to increased vagal tone but later due to the direct effect of cyanide on the heart. Hyperventilation in the trout persisted throughout the exposure period, although the rate and amplitude fluctuated and was variable between individual fish. During the last hour of exposure (highest cyanide concentration), ventilation was characterized by rapid, shallow breaths followed by a sudden respiratory arrest. The bullheads exhibited hyperventilation during the first 3 hours of exposure followed by a gradual, linear drop in ventilation rate and amplitude until death occurred. Cardiac and ventilatory responses in both species were attributed to stimulation of central and peripheral chemoreceptors by cyanide. Evidence is presented which suggests the initial response in the bullheads was due, at least in part, to gustatory stimulation by the cyanide. Oxygen consumption of the trout remained above pre-exposure levels for the majority of the test period. Oxygen consumption in the bullhead paralleled the changes in heart and ventilatory rates. Whole-body lactate levels of fingerlings of both species during cyanide exposure were measured to estimate the extent of anaerobiosis. Whole-body lactate levels were much greater in the bullheads than the trout, indicating a higher capacity for anaerobiosis, possibly due to a greater fuel supply. Overall, the trout responded to cyanide in a manner similar to that produced by environmental hypoxia whereas the bullheads experienced a gustatory stimulus which masked the hypoxia-like response.     

An overview of stress physiology of fish transport: changes in water quality as a function of transport duration

This study brings an integrated analysis about the relationship between water deterioration and its physiological consequences in live fish transport. The analysis was focused on the transport water and its deterioration, and physiological challenges imposed on the fish. Usual commercial handling procedures employed to mitigate fish stress during transport were discussed. Future topics of research for the establishment of safer fish transport protocols were proposed. Transport was classified into short (≤8 h) or long transport (>8 h). The main issue in short transports should be the prevention of water pH reduction, while in long transports it is the increase in ammonia. Plasma cortisol is the most employed marker for stress and is acutely elevated upon short episodes of transport, but remains elevated even in long‐transport events. Plasma glucose is perhaps a better marker for handling stress. Plasma lactate, pH, osmolality CO₂ and ions should be more often evaluated. Plasma Na⁺ and Cl^‐ are very useful markers of acidosis, due to their respective exchange for H⁺ and , for acid–base regulation. The establishment of species‐specific transport protocols should be preceded by such combined analyses of water and physiological parameters.     

Are hatchery‐reared abalone naïve of predators? Comparing the behaviours of wild and hatchery‐reared northern abalone,Haliotis kamtschatkana (Jonas, 1845)

Abalone populations have declined worldwide, generating interest in enhancement using hatchery‐reared individuals. In many cases, such restoration efforts have met with limited success due to high predator‐induced mortality rates. Furthermore, the mortality rates of outplanted hatchery abalone are often considerably higher than for wild individuals. This study uses northern abalone (Haliotis kamtschatkana) as a case study to determine whether hatchery‐reared abalone behave differently than their wild counterparts. In the field, outplanted hatchery‐reared abalone were significantly less responsive than wild abalone, in terms of number of abalone responding and intensity of response, to nearby movement and to physical contact with an inert probe. Also, when encountering a cue to which all abalone responded (a seastar predator), hatchery‐reared individuals remained subdued. Anti‐predator behavioural deficits in hatchery‐reared abalone were more pronounced in 4‐year‐old individuals than in 1‐year‐old individuals, suggesting an influence of either age or amount of time spent in the hatchery environment. These behavioural differences are expected to increase the vulnerability of hatchery‐reared abalone to predators, and are likely a major cause of their elevated predator‐induced mortality when outplanted.     

Effects of cadmium on the kinetics of calcium uptake in developing tilapia larvae, Oreochromis mossambicus

The toxic effects of Cd²⁺ on Ca²⁺ influx kinetics in developing tilapia (Oreochromis mossambicus) larvae were evaluated. Addition of 20 µg l^-1 of Cd²⁺ to the environment of 0 and 3 day-old larvae competitively inhibited the Ca²⁺ uptake within 4h resulting in a great increase in K_m values for Ca²⁺ influx (19.3 and 17.4 fold, respectively) as compared with their respective controls. Consequently, the actual Ca²⁺ influx of larvae in solutions of 0.2 mM Ca²⁺ are suppressed by 32–45%. Also, 3 day-old larvae were more sensitive to internally accumulated Cd²⁺ than 0 day-old larvae. Although the Ca²⁺ influx in 0 and 3 day-old larvae may be restored to the levels of their respective controls with 24h of being transferred to a 20 µg l^-1 Cd²⁺ solution, total body Ca²⁺ content was significantly reduced in 3 day-old larvae. Increased Ca²⁺ uptake efficiency ensures sufficient Ca²⁺ for normal growth. However, rapid increase in Ca²⁺ influx after hatching also leads to higher Cd²⁺ uptake. Exposure to Cd²⁺ will lead to a drop in body Ca²⁺ content resulting in retardation of larval growth. Therefore, we conclude that if Ca²⁺ uptake is interfered with at this critical stage of development, larvae will not be able to maintain normal levels of body Ca²⁺ and will show signs of Cd²⁺ poisoning.     

Migratory dynamics of stream-spawning longnose gar (Lepisosteus osseus)

Abstract– Literature evidence suggests that lake-dwelling longnose gar (Lepisosteus osseus) enter tributary streams to spawn, Until the present study, the dynamics of this breeding migration had never been investigated quantitatively. During the summers of 1991 and 1992, longnose gar were captured as they entered Weaubleau Creek, Missouri, a tributary of Harry S. Truman Reservoir. The in-stream spawning migration began in early April and ended in late May, and was positively correlated with stream flow and water level, and negatively correlated with water temperature. In-stream residence times ranged from 15 to 94 days, with males exhibiting longer residence times than females. Once in-stream, longnose gar travelled as far as 10 km upstream and occupied certain pools at greater relative frequencies. Although the reason for this preferential utilization is not completely understood, it may relate to pool depth and riffle proximity. Longnose gar disperse from the spawning stream great distances, with gar captured in Weaubleau Creek being recaptured up to 48 km away. This information should provide fisheries biologists the means to consider the reproductive ecology of this species in their conservation and management decisions.     

Nutritional regulation of hepatocyte fatty acid desaturation and polyunsaturated fatty acid composition in zebrafish (Danio rerio) and tilapia (Oreochromis niloticus)

The desaturation and elongation of [1-¹⁴C]18:3n-3 was investigated in hepatocytes of the tropical warm freshwater species, zebrafish (Danio rerio) and Nile tilapia (Oreochromis niloticus). The hepatocyte fatty acid desaturation/elongation pathway was assayed before and after the fish were fed two experimental diets, a control diet containing fish oil (FO) and a diet containing vegetable oil (VO; a blend of olive, linseed and high oleic acid sunflower oils) for 10 weeks. The VO diet was formulated to provide 1% each of 18:2n-6 and 18:3n-3, and so satisfy the possible EFA requirements of zebrafish and tilapia. At the end of the dietary trial, the lipid and fatty acid composition was determined in whole zebrafish, and liver, white muscle and brain of tilapia. Both zebrafish and tilapia expressed a hepatocyte fatty acid desaturation/elongation pattern consistent with them being freshwater and planktonivorous fish. The data also showed that hepatic fatty acid desaturation/elongation was nutritionally regulated with the activities being higher in fish fed the VO diet compared to fish fed the FO diet. In zebrafish, the main effect of the VO diet was increased fatty acid Δ6 desaturase activity resulting in the production of significantly more 18:4n-3 compared to fish fed the FO diet. In tilapia, all activities in the pathway were greater in fish fed the VO diet resulting in increased amounts of all fatty acids in the pathway, but primarily eicosapentaenoic acid (EPA; 20:5n-3) and docosahexaenoic acid (DHA; 22:6n-3). However, the fatty acid compositional data indicated that despite increased activity, desaturation of 18:3n-3 was insufficient to maintain tissue proportions of EPA and DHA in fish fed the VO diet at the same level as in fish fed the FO diet. Practically, these results indicate that manipulation of tilapia diets in commercial culture in response to the declining global fish oil market would have important consequences for fish fatty acid composition and the health of consumers. Scientifically, zebrafish and tilapia, both the subject of active genome mapping projects, could be useful models for studies of lipid and fatty acid metabolism at a molecular biological and genetic level. This revised version was published online in August 2006 with corrections to the Cover Date.