PCR‐DGGE analysis of the autochthonous gut microbiota of grouper Epinephelus coioides following probiotic Bacillus clausii administration

The autochthonous microbiota in the foregut, midgut and hindgut of juvenile grouper Epinephelus coioides following the dietary administration of probiotic Bacillus clausii for 60 days were assessed using polymerase chain reaction‐denaturing gradient gel electrophoresis (PCR‐DGGE). A complex and generally similar bacterial composition along the digestive tract of E. coioides was detected in the DGGE profiles, while several bacteria showed regional specialization. Similarity dendrogram revealed that the bacterial composition of the foregut was more similar to the midgut than the hindgut. Samples collected from the probiotic group and the control group showed generally similar DGGE patterns, while no significant difference in the total number of bands and Shannon index were observed between the probiotic group and the control group, suggested that probiotic B. clausii exerted no significant effect on the gut microbiota of E. coioides. However, various potentially beneficial bacteria, such as Enterococcus sp.‐like and Bacillus pumilus‐like bacterium were selectively stimulated by probiotic B. clausii, while some potential harmful species, like Staphylococcus sp.‐like and Vibrio ponticus‐like bacterium were depressed. These indicated that the gut microbiota was modified to some degree by probiotic B. clausii. Sequences analysis showed that the autochthonous gut bacteria of E. coioides could be classified into four groups, i.e. Proteobacteria, Firmicutes, Actinobacteria and unclassified bacteria.     

Culture-independent characterization of the autochthonous gut microbiota of grouper Epinephelus coioides following the administration of probiotic Enterococcus faecium

Probiotics have been applied extensively in aquaculture and demonstrated a range of benefits, but the mechanisms mediating such responses remain largely unknown. A clear illustration of the effect of probiotics on the autochthonous gut microbiota is the first step in understanding the underlying mechanisms. In this study, the autochthonous microbiota in the foregut, midgut and hindgut of juvenile grouper Epinephelus coioides following the dietary administration of probiotic Enterococcus faecium MM4 for 60?days were assessed using polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) with subsequent sequencing analysis. Generally similar DGGE patterns, with 15 common bands, were observed in the foregut, midgut and hindgut of fish fed the probiotic diet or the control diet, while more visible bands were present in fish fed the probiotic diet. The similarity dendrogram showed that the foregut samples formed an independent cluster distinctly different from the midgut and hindgut samples, but a high similarity (81.4%) was observed among the three gut sections. Significantly increased species richness and Shannon index were observed in the midgut and hindgut samples in the probiotic group compared with the control group, which suggested that probiotic E. faecium could elevate the autochthonous microbial diversity in the midgut and hindgut. Sequences analysis showed that probiotic E. faecium stimulated the growth of some unidentified bacteria and potentially beneficial bacteria, while exerted no apparent effect on potentially harmful Staphylococcus saprophyticus.     

Effect of Lactococcus lactis and Enterococcus faecium on growth performance,digestive enzymes and immune response of grouper Epinephelus coioides

The effect of dietary administration of Lactococcus lactis MM1 and Enterococcus faecium MM4, two strains of lactic acid bacteria isolated from the gut of juvenile grouper Epinephelus coioides, on the growth, feed utilization, digestive enzymes and immune response of juvenile E. coioides was evaluated. The fish were fed for 60 days with three different diets: control diet (without probiotic), diet P1 supplemented with 1.0 × 10⁸ CFU g^?1L. lactis or diet P2 with 1.0 × 10⁸ CFU g^?1E. faecium. Although growth and feed intake decreased slightly, significant improvement of feed utilization was observed in fish fed diet P1 and diet P2 for 60 days. The hepatopancreatic protease activities in the two probiotic treatments were significantly higher than that in the control. The phagocytic activity, serum superoxide dismutase activity and complement component 4 (C4) and IgM levels were not significantly affected by diet P1 and diet P2. Serum complement component 3 (C3) levels in the two treatments were significantly higher than that in the control. Significant increased serum lysozyme activity was observed in fish fed the diet P1, while significant decreased lysozyme activity was observed in fish fed the diet P2 compared with the fish fed the control diet. There was a significant interaction effect between diet and administration date for the complement C4. The study demonstrates potential for L. lactis MM1 and E. faecium MM4 to improve the feed utilization and modulate the immune function in E. coioides.     

Bacterial community composition and distribution in different segments of the gastrointestinal tract of wild‐caught adult Penaeus monodon

Bacterial community associated with the gastrointestinal (GI) tract of aquaculture animals can play important roles in health, nutrition and disease. Compared with the GI tract of aquatic vertebrates such as fish, crustacean GI tract has unique structures and surfaces in different segments that may contribute to differences in the bacterial communities. This study examined the bacterial composition and distribution in different segments along the GI tract and in digesta of wild‐caught adult Penaeus monodon using Automated Ribosomal Intergenic Spacer Analysis (ARISA), real‐time quantitative PCR and clone libraries of 16S rRNA genes. Thirty‐nine bacterial species in four phyla including Proteobacteria (α, β, ε, γ), Firmicutes, Bacteroidetes and Actinobacteria were represented in the GI tract of adult P. monodon. Proteobacteria comprised over 80% abundance of the bacterial community in most segments of the GI tract, except the middle intestine that was dominated by Firmicutes (~50% abundance). The results also showed that bacterial communities showed significant differences along the GI tract segments, particularly the hindgut (p < .001) with Vibrio and Ferrimonas as dominant genera. The knowledge about the distribution of bacteria could be useful in understanding interaction of commensal bacteria and pathogens in different segments, and its potential influence on the effectiveness of probiotic bacteria in the GI tract of shrimp.     

温度对施氏鲟幼鱼摄食、生长和肠道消化酶活性的影响

研究不同养殖温度(15℃、18℃、21℃、24℃、27℃)对施氏鲟(Acipenser schrenckii)幼鱼摄食、生长和肠道消化酶活性的影响。结果表明,在15～24℃范围内,幼鱼的特定生长率(SGR)和相对增重率(RWG)随温度的升高而显著增加(P<0.05),均在24℃时达到最高值;随着温度升高,其饵料系数(FC)先降低后升高(P<0.05),且在24℃时达到最小值;此外,摄食率(FR)随着温度的升高而显著升高(P<0.05),其不同温度组的生长速度由高到低依次为24℃、21℃、27℃、18℃、15℃组。温度对幼鱼前肠蛋白酶活性影响显著,24℃组和27℃组前肠的蛋白酶活性显著低于15℃组(P<0.05),而温度对中肠和后肠蛋白酶活性则无显著性影响(P>0.05);温度对幼鱼肠道脂肪酶活性无显著性影响(P>0.05),各温度组前肠脂肪酶活性均高于中肠和后肠;温度对幼鱼肠道淀粉酶活性无显著性影响(P>0.05)。综合以上结果认为,施氏鲟幼鱼快速生长的适宜温度范围为21～24℃,在此温度范围内施氏鲟幼鱼可获得最大生长率和存活率。     

Purification and characterization of stomach protease from the turbot (Scophthalmus maximus L.)

Proteolytic activity in the different parts of the digestive tract of the turbot (Scophthalmus maximus L.) were studied in this work. One pure protease was isolated from turbot stomach and its behavior was studied. Results showed the optimum pH for proteases in the different parts of the digestive tract of the turbot were pH 2.0 for the stomach, pH 8.0 for the pylorus cecum, pH 8.0 for the foregut, pH 8.5 for the midgut, and pH 8.0 for the hindgut. The activity of proteases in the different parts of the digestive tract were in the sequence pylorus cecum protease > stomach protease > foregut protease > midgut protease > hindgut protease. The stomach protease was purified by ammonium sulfate precipitation and column chromatography on DEAE-Sepharose F.F. and Sephadex G-100. The purified enzyme gave a single band in SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Its molecular weight was found to be approximately 42,000 Da. The enzyme is stable at pH 1.0–9.0 and at temperatures below 40°C. Its activity was maximum at pH 2.0 and 40°C. When reaction time was prolonged the optimum temperature of the enzyme tended to decline. The enzyme was activated by Mn²⁺ and Cu²⁺ and inactivated by Fe³⁺. It was fully inhibited by pepstatin and partially inhibited by PMSF, TPCK, PCMB, and NBS. These results imply the enzyme is a pepsin.     

Effect of dietary administration of Psychrobacter sp. on the growth,feed utilization,digestive enzymes and immune responses of grouper Epinephelus coioides

A 60‐day feeding trial was conducted to assess the effect of incorporating dietary Psychrobacter sp., one predominant bacterium with antagonistic activity in the gut of fast‐growing grouper Epinephelus coioides, on the growth, feed utilization, digestive enzymes and immune responses of E. coioides at regular monthly intervals. The fish were fed with control diet (without probiont) or probiotic diet supplemented with 1.0 × 10⁸ CFU g^?1Psychrobacter sp. No significant improvement in weight gain (WG) and specific growth ratio (SGR) were observed in the probiotic group, but a significant improvement in feed conversion ratio (FCR) was observed in fish fed the probiotic diet for 60 days. Although not statistically significant, enhanced hepatopancreatic protease and lipase activities and intestinal amylase activity were observed in probiotic group at day 60. A slightly increase in phagocytic activity and phagocytic index was observed in fish fed probiotic diet for 60 days. Serum lysozyme activity showed no significant differences between the probiotic group and the control group during the whole experiment period, while an increasing trend of superoxide dismutase (SOD) activity in the probiotic group was observed. Serum complement component 3 (C3) level of the probiotic group was higher than that of control in the whole feeding period, while complement component 4 (C4) level of the probiotic group was significantly higher than that of the control at day 60. The results of the current study firstly demonstrated potential for Psychrobacter sp. as a novel probiont to improve feed utilization, digestive enzymes and innate immunity in E. coioides.     

Characterization of the bacterial community in different parts of the gut of sea cucumber (Apostichopus Japonicus) and its variation during gut regeneration

Bacterial community plays an important role in keeping the health status of the host. A study on the characteristics of gut bacterial community of sea cucumber (Apostichopus japonicus) not only helps improve the current aquaculture model, but promotes healthy and rapid development of the aquaculture industry as well. Therefore, taking pond‐cultured sea cucumber (A. japonicus) as the studying object, the metagenomic and 16S rRNA sequencing technology were used in this study to explore the characteristics of bacterial community in different parts of the gut of sea cucumber, as well as during gut regeneration after evisceration. The results showed that the compositions of bacterial community are different in varying parts of the gut of sea cucumber (A. japonicus). Specifically, bacterial community in the midgut and hindgut are highly similar, showing significantly diversified bacterial species compared to the foregut. GO annotation indicated that the foregut is associated with richer catalytic activity and binding than the midgut and the hindgut. According to the KEGG annotation, metabolism‐related genes are mainly concentrated in the foregut, while genes related to signal transduction and the immune system are mostly annotated in the midgut and hindgut. During the gut regeneration stage, the structure of bacterial community varied greatly in different stage of the regeneration stage, with significant differences between the earlier and later stage. The dominant bacteria in the earlier stage is Rubritalea, and that in the later stage is Arcobacter. Besides, there were Loktanella, Thalassobacter and Phaeobacter in the gut throughout the entire regeneration stage. Cupriavidus, Hellea, HTCC2207, Methylophaga, Methylotenera, Stenotrophomonas and Tenacibaculum were only present in the earlier stage, and gradually disappeared in the later stage due to improving gut functions. The abundance and diversity of bacteria in the gut were higher in the earlier regeneration stage than that in the later stage, with a peak between the 15th and 25th day of the regeneration stage. At 45th day, the abundance and diversity became stable.     

Phytase-producing bacteria in the digestive tracts of some freshwater fish

Isolation and enumeration of phytase‐producing bacterial flora in the foregut and hindgut regions of the gastrointestinal tracts of 10 culturable freshwater teleosts of different feeding habits, namely rohu (Labeo rohita), catla (Catla catla), mrigal (Cirrhinus mrigala), bata (Labeo bata), kalbasu (Labeo calbasu), Nile tilapia (Oreochromis niloticus), climbing perch (Anabas testudineus), common carp (Cyprinus carpio), silver carp (Hypophthalmichthys molitrix) and grass carp (Ctenopharyngodon idella), have been carried out. Microbial culture of the gut mucosa on selected nutrient media following the enrichment culture technique was performed for bacterial isolation. The bacterial isolates were screened on the basis of their enzyme‐producing ability. The bacterial population on the tryptone soya agar (TSA) plate was maximum in the hindgut region of bata, followed by mrigal and minimum in the foregut region of Nile tilapia. In modified phytase screening medium (MPSM), phytase‐producing strains were recorded at higher densities in the foregut region of mrigal and grass carp and minimum in the foregut region of bata. In case of the hindgut, maximum phytase‐producing strains were present in grass carp and mrigal and minimum in rohu. In general, in MPSM, the bacterial population was lower in the hindgut region of all the 10 species of fish examined. The phytase‐producing ability of the selected 31 strains (16 from the foregut and 15 from the hindgut region) was determined by clearing zones on phytate‐containing plates. Among these isolates, 22 strains (12 from the foregut and 10 from the hindgut region) were selected as potent phytase producers according to a quantitative enzyme assay. The highest phytase activity was observed in the bacterial strains LF1 and LH1 isolated from the fore and the hindgut regions of rohu respectively. Both the strains were identified as Bacillus licheniformis on the basis of phenotypic characteristics as well as 16S rDNA sequence analysis.     

圆尾鲎与中国鲎消化道形态学与组织学观察

比较分析圆尾鲎和中国鲎消化道组织学和形态学特征,为其发育生物学的研究和健康繁育提供理论依据。中国鲎与圆尾鲎均来自于广西合浦县西场镇邻近海域,10龄和14龄均各5只,平均头胸甲宽:圆尾鲎46.78~52.42 mm、中国鲎46.09~55.44 mm。通过形态解剖、组织切片和光镜技术等对消化道的形态学与组织学特征进行研究。结果表明:圆尾鲎与中国鲎消化道外部及解剖形态基本相似;它们的消化道可划分为前肠(口道、食道、前胃、幽门)、中肠和后肠(直肠、肛门);前肠、中肠和后肠都由几丁质层、粘膜层、粘膜下层、肌层及外膜组成,但是中肠不含几丁质层。10龄中国鲎和圆尾鲎的消化道总长以及中肠长度差异显著,消化道其余各部分的长度差异不显著。不同龄同种鲎以及同龄不同种鲎间的所有测量指数差异显著。消化道各部分的结构、组织形态均与其杂食性密切相关。     

饲料蛋白水平对不同规格凡纳滨对虾蛋白质表观消化率和消化酶活性的影响

为探究饲料蛋白水平对拉萨裸裂尻 (Schizopygopsis younghusbandi) 幼鱼肠道和肝脏的消化酶活性及组织结构的影响,设计出蛋白质水平分别为20%、25%、30%、35%、40%、45%的6种等脂等能的饲料,饲喂初始体质量为 (22.42±0.56) g的拉萨裸裂尻幼鱼60 d。结果显示,随着饲料蛋白水平升高,肠道和肝脏的蛋白酶活性呈先升高后降低的趋势,其中35%蛋白水平组蛋白酶活性显著高于其他实验组 (P<0.05)。脂肪酶和淀粉酶活性随着饲料蛋白水平的升高呈降低趋势 (P<0.05)。前、中、后肠的管壁厚度和绒毛高度呈先升高后降低的趋势 (P<0.05),其中在30%蛋白水平组的前肠和中肠管壁厚度最高,35%蛋白水平组后肠管壁厚度最高,30%蛋白水平组前肠、中肠和后肠绒毛高度最高。饲料蛋白水平高于35%时会损伤肝脏组织结构。在该实验条件下,综合考虑鱼体肠道和肝脏中消化酶活性及组织结构,拉萨裸裂尻幼鱼饲料蛋白水平以30%为宜。

     

Role of gastrointestinal microbiota in fish

The gastrointestinal (GI) tract of an animal consists of a very complex and dynamic microbial ecosystem that is very important from a nutritional, physiological and pathological point of view. A wide range of microbes derived from the surrounding aquatic environment, soil/sediment and feed are found to colonize in the GI tract of fish. Among the microbial groups, bacteria (aerobic, facultative anaerobic and obligate aneraobic forms) are the principal colonizers in the GI tract of fish, and in some fish, yeasts are also reported. The common bacterial colonizers in the GI tract of freshwater and marine fish include Vibrio, Aeromonas, Flavobacterium, Plesiomonas, Pseudomonas, Enterobacteriaceae, Micrococcus, Acinetobacter, Clostridium, Fusarium and Bacteroides, which may vary from species to species as well as environmental conditions. Besides, several unknown bacteria belonging to Mycoplasma, Arthrobacter, Brochothrix, Jeotgailbacillus, Ochrobactrum, Psychrobacter and Sejongia species in the GI tract of different fish species have now been identified successfully using culture‐independent techniques. Gnotobiotic and conventional studies indicate the involvement of GI microbiota in fish nutrition, epithelial development, immunity as well as disease outbreak. This review also highlights the need for manipulating the gut microbiota with useful beneficial microbes through probiotic, prebiotic and synbiotic concepts for better fish health management.     

草鱼和银鲫肠道产消化酶细菌的研究

检测了分别从草鱼(Ctenopharyngodon idellus)和银鲫(Carassius auratus gibelio)肠道中分离的180株细菌的蛋白酶、脂肪酶、淀粉酶和纤维素酶的产酶能力。结果显示,两种鱼肠道内可分泌胞外消化酶的细菌包括Aero-monas(气单胞菌属,Aer.)、Vibrio(弧菌属,Vib.)、Bacillus(芽孢杆菌属,Bac.)、Pseudomonas(假单胞菌属,Pse.)四个种属的细菌,Aer.在其中占主要优势,45.71%的Aer.可分泌胞外消化酶。草鱼可分泌上述四种胞外消化酶的菌株共有33株,占肠道菌总数的36.67%;银鲫43株,占47.78%。产酶菌的分布上,草鱼中肠内产消化酶细菌数量显著多于前肠和后肠(P<0.05),前、中、后肠分别是6株、20株和7株;银鲫中肠和后肠数量差异不显著,前肠分布最少。草鱼分泌蛋白酶、脂肪酶、淀粉酶和纤维素酶的菌株分别有21株(23.33%)、10株(11.11%)、30株(33.33%)和16株(17.78%)。银鲫肠道内未检测到可分泌纤维素酶的细菌,蛋白酶、脂肪酶和淀粉酶菌株的数量分别是21株、37株和17株。可见鱼类肠道细菌对食饵消化有重要作用。     

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。     

Lactic acid bacteria vs. pathogens in the gastrointestinal tract of fish: a review

Intensive fish production worldwide has increased the risk of infectious diseases. However, before any infection can be established, pathogens must penetrate the primary barrier. In fish, the three major routes of infection are the skin, gills and gastrointestinal (GI) tract. The GI tract is essentially a muscular tube lined by a mucous membrane of columnar epithelial cells that exhibit a regional variation in structure and function. In the last two decades, our understanding of the endocytosis and translocation of bacteria across this mucosa, and the sorts of cell damage caused by pathogenic bacteria, has increased. Electron microscopy has made a valuable contribution to this knowledge. In the fish‐farming industry, severe economic losses are caused by furunculosis (agent, Aeromonas salmonicida spp. salmonicida) and vibriosis [agent, Vibrio (Listonella) anguillarum]. This article provides an overview of the GI tract of fish from an electron microscopical perspective focusing on cellular damage (specific attack on tight junctions and desmosomes) caused by pathogenic bacteria, and interactions between the ‘good’ intestinal bacteria [e.g. lactic acid bacteria (LAB)] and pathogens. Using different in vitro methods, several studies have demonstrated that co‐incubation of Atlantic salmon (Salmo salar L.) foregut (proximal intestine) with LAB and pathogens can have beneficial effects, the cell damage caused by the pathogens being prevented, to some extent, by the LAB. However, there is uncertainty over whether or not similar effects are observed in other species such as Atlantic cod (Gadus morhua L.). When discussing cellular damage in the GI tract of fish caused by pathogenic bacteria, several important questions arise including: (1) Do different pathogenic bacteria use different mechanisms to infect the gut? (2) Does the gradual development of the GI tract from larva to adult affect infection? (3) Are there different infection patterns between different fish species? The present article addresses these and other questions.     

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

比较研究了卵形鲳鲹（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。卵形鲳鲹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。     

军曹鱼消化系统的形态及组织学研究

利用活体解剖和光镜技术对军曹鱼Rachycentron canadum消化系统进行形态及组织学研究。结果显示,军曹鱼消化道由口咽腔、食道、胃、幽门盲囊、前肠、中肠和后肠几部分组成。口咽腔大,粘膜上皮为复层鳞状上皮,内含少量杯状细胞。食道很短,但上皮包括复层鳞状上皮区和单层柱状上皮区。胃膨大,呈Y形,在贵门和幽门部可观测到杯状细胞,胃体粘膜层下有大量的胃腺细胞。幽门盲囊发达,肠短但分3部分,前肠、中肠和后肠,肠道系数为0．43,肠道由前向后杯状细胞和粘膜皱褶不断减少。消化腺包括肝脏和胰腺,肝小叶分界不明显,肝细胞内脂肪含量丰富,胰腺属于散在性的,其外分泌部有许多腺泡组成,胰岛分散于外分泌部间。     

宽口裂腹鱼消化系统解剖和组织学观察

该研究采用解剖、石蜡切片和HE染色法对宽口裂腹鱼(Schizothorax eurystomus)消化系统解剖特征和组织切片进行观察。结果显示,其消化管管壁由内向外分别为黏膜层、黏膜下层、肌层和浆膜,主要差别在于黏膜层和肌层。食道黏膜上皮为复层扁平上皮,上皮间分布有大量杯状细胞;前肠和中肠黏膜上皮为单层柱状上皮,明显可见刷状缘、杯状细胞和淋巴细胞分布其间;后肠黏膜上皮为假复层柱状上皮,其间也有杯状细胞和淋巴细胞分布,肠道中杯状细胞由前至后逐渐增多。食道肌层为内环外纵的骨骼肌;前肠肌层为内环外纵的平滑肌;中肠和后肠为内螺旋外环行的平滑肌。消化腺由肝脏和胰腺组成,胰腺弥散状分布在肝脏中,肝小叶不明显。研究表明,宽口裂腹鱼消化系统组织学特征与其食性具有适应性。     

Stages of rock bream oplegnathus fasciatus (Temminck et Schlegel 1844): embryonic development

The embryonic development of rock bream, Oplegnathus fasciatus, was studied from fertilization until hatching. The hatching occurred approximately at 25 h after fertilization at 23.5 ± 0.5 °C. The embryogenesis is divided into seven stages: Zygote period, Cleavage period, Morula period, Blastula period, Gastrula period, Segmentation period and Hatching period. The first cleavage furrow of rock bream fertilized eggs is vertically oriented, as is usual until horizontal cleavage occurs at the fifth cleavage. The blastocoel is observed between the blastoderm and I‐YSL at blastula period. At 90%‐epiboly stage, the earliest somitic furrow appears in the middle of embryo. The myotomes develop from somites at 15 h 30 min post fertilization. The Kupffer's vesicle consisting of ventrally I‐YSL and dorsally columnar cells appears with the completion of epiboly. It degenerates gradually with the penetration of some eosinophilic granules and disappears completely at 20 h 30 min after fertilization. The digestive tract, a straight tubule, is differentiated into foregut, midgut and hindgut. The epithelium of midgut and hindgut are the monolayer cubic and columnar cells respectively. The staging series provides a preliminary baseline reference for future studies on embryos of the rock bream.