Histochemical and immunohistochemical characterization of rodlet cells in the intestine of two teleosts,Anguilla anguilla and Cyprinus carpio

Rodlet cells (RC) are characterized by a distinctive cell cortex and conspicuous inclusions named “rodlets.” These cells are particularly abundant and large in size in intestine of eels. Histochemical, immunohistochemical and ultrastructural investigations were carried out on European eel Anguilla anguilla and Common carp Cyprinus carpio from Northern Italy. Eight biotinylated lectins were used to probe for specific carbohydrate residues in deparaffinized, hydrated intestinal sections of eel and carp. Five antibodies were tested on intestinal sections of both fish species: inducible nitric oxide synthase (i‐NOS), leu‐enkephalin, lysozyme, serotonin and tumour necrosis factor‐α. Lectin histochemistry revealed rodlet cells (RCs) of the eel intestine to react with two of the eight lectins tested, specifically Concanavalin A (ConA) and Sambucus Nigra Agglutinin (SNA). This contrasted to lectin staining of RCs in the intestine of common carp, where four of the eight lectins showed a positive reaction; Dolichos Biflorus Agglutinin (DBA), Wheat Germ Agglutinin (WGA), SNA and ConA. RCs in eel and carp intestine were immunoreactive with antibodies to lysozyme and i‐NOS. The occurrence of the inflammatory peptides lysozyme and i‐NOS in RCs of the eel and common carp poses in favour that these cells are involved in the mechanism of defence against pathogens.     

Protective responses of intestinal mucous cells in a range of fish–helminth systems

Histopathological, immunofluorescence and ultrastructural studies were conducted on the intestines of four fish species infected with different taxa of enteric helminths. Brown trout (Salmo trutta trutta), eel (Anguilla anguilla) and tench (Tinca tinca) obtained from Lake Piediluco (central Italy) were examined. Brown trout and eel were infected with two species of acanthocephalans, and tench was parasitized with a tapeworm species. In addition to the above site, specimens of chub (Squalius cephalus) and brown trout infected with an acanthocephalan were examined from the River Brenta (north Italy). Moreover, eels were examined from a brackish water, Comacchio lagoons (north Italy), where one digenean species was the predominant enteric worm. All the helminths species induced a similar response, the hyperplasia of the intestinal mucous cells, particularly of those secreting acid mucins. Local endocrine signals seemed to affect the production and secretion of mucus in the parasitized fish, as worms often were surrounded by an adherent mucus layer or blanket. This is the first quantitative report of enteric worm effects on the density of various mucous cell types and on the mucus composition in intestine of infected/uninfected conspecifics. We provide a global comparison between the several fish–helminth systems examined.     

Histopathological changes induced by the digenean intestinal parasite Masenia nkomatiensis Dumbo,Dos Santos, & Avenant‐Oldewage, 2019 of the catfish Clarias gariepinus (Burchell) from Incomati Basin,Mozambique

The intestines of 154 Clarias gariepinus were examined of which 29 were naturally infected with Masenia nkomatiensis, and of these, seven (intensity ranging from 8 to 231) were examined for pathology. Destruction of the epithelium covering the villi, detachment of epithelial cells and parts of villi were observed. Excessive mucus secretion occurred in the vicinity of the worm and catarrh was observed, indicative of an inflammatory response. The number of mucous and mast cells was higher at the attachment site than at an area 5,000 µm away and in uninfected individuals, suggesting that the parasite triggered a localized innate immune response. The number of neutrophils, basophils and lymphocytes in infected tissue was not significantly different from uninfected tissue confirming that no acquired immune response was produced against the maseniid. The caecae in the anterior part of the parasites' intestine consisted of convoluted epithelium forming invaginations or “crypts.” Contraction of the thick layer of circular muscle fibres of the caeca facilitates the movement of digested material. Observation of digested host cells and cell debris within the caecae provides further evidence that M. nkomatiensis is consuming host cells.     

Study of the distribution of active caspase‐3‐positive cells in turbot,Scophthalmus maximus (L.), enteromyxosis

Enteromyxosis caused by Enteromyxum scophthalmi is one of the parasitizations with a higher economic impact on turbot, Scophthalmus maximus (L.), aquaculture. This myxosporean produces severe catarrhal enteritis with abundant inflammatory infiltrates in the lamina propria‐submucosa (LP), epithelial detachment and leucocyte depletion of the lymphohaematopoietic organs. Some advances made on the pathogenesis pointed to a role of apoptosis in the enteromyxosis. Therefore, the main aim of this work was to employ the TUNEL assay and the anti‐(active caspase‐3) immunohistochemical assay to detect apoptotic cells in both healthy and E. scophthalmi‐infected turbot in order to establish the presence and distribution of apoptotic cells during development of the disease. More apoptotic cells located within the gastrointestinal epithelium were observed in the initial stages of the infection in E. scophthalmi‐infected turbot compared with non‐infected turbot. As the infection progressed, a higher degree of apoptosis occurred in the epithelium of folds heavily parasitized. In the severely infected turbot, apoptosis was also found among the leucocytes of the intestinal inflammatory infiltrates. Moreover, the number of active caspase‐3‐positive cells in the lymphohaematopoietic organs tended to increase with disease severity. In view of the results, increased apoptosis in the epithelium may favour the scaling that occurs during enteromyxosis and cell death of leucocytes in the intestinal LP, contributing to leucocyte depletion in severe cases.     

Immunological effects of glucan and <Emphasis Type="Italic">Lactobacillus rhamnosus</Emphasis> GG,a probiotic bacterium,on Nile tilapia <Emphasis Type="Italic">Oreochromis niloticus</Emphasis> intestine with oral <Emphasis Type="Italic">Aeromonas</Emphasis> challenges

The present study histologically examined the effects of glucan-containing and Lactobacillus rhamnosus GG (LGG)-containing diets on intestinal damages inflicted on Nile tilapia by Aeromonas challenges. Tilapia were fed control, glucan, and LGG diets for 2 weeks and were subsequently challenged with Aeromonas. The intestines were then histologically examined at 1, 7, 14, and 21 days post-infection. Mortality following the challenge was lower for the fish fed the glucan and LGG diets. The intestines of these groups also showed increased inflammatory cell infiltration and reduced intestinal damage from Aeromonas. Moreover, inflammatory cell infiltration occurred more rapidly in the glucan-fed than in the LGG-fed fish following the challenge. Before the challenge, the dominant mucous cell was the acid type in all the tests. After the challenge, the main mucus cell type in the proximal intestine of the glucan-fed fish shifted to AB-PAS double-staining cells, while in the LGG-fed fish, it remained the acid type throughout the test period, and the number of double-staining cells was smaller than in the control fish after the challenge. Thus, the different mucous cell and inflammatory cell responses show that glucan and LGG might have different immunostimulative effects, although they both reduced the intestinal damage following Aeromonas challenges.     

塔里木裂腹鱼消化系统形态学与组织学研究

利用传统石蜡切片、HE染色等方法对塔里木裂腹鱼(Schizothorax biddulphi)消化系统形态学和组织学特征进行研究。结果显示,塔里木裂腹鱼消化系统由消化管和消化腺组成,消化管包括口咽腔、食道和肠(前肠、中肠、后肠和直肠)。口咽腔内具有发达的咽齿。无胃,肠与食道紧接,前肠膨大。消化道由腔面向外依次为黏膜层、黏膜下层、肌层和浆膜层,但口咽腔只有黏膜层、黏膜下层和肌层,未发现有浆膜层。消化道4层中,黏膜层差异最大：口咽腔黏膜层为复层扁平上皮,其间分布有味蕾和大量黏液细胞;食道粗而短,黏膜层为复层扁平上皮,黏膜褶两侧分布大量黏液细胞,且固有膜血管丰富;肠道上皮细胞为单层柱状上皮,上皮间分布有杯状细胞,其数量由前向后逐渐增加,而黏膜褶高度逐渐降低。消化腺由肝脏和胰脏组成,肝脏的肝小叶不明显,但明显可见肝血窦及中央静脉分布,肝门管区不典型。胰脏仅在肠系膜中出现,而未在其他组织中发现,胰小叶间中央静脉明显,中央静脉中可见大量椭圆形有核的红细胞。本研究对塔里木裂腹鱼消化系统形态学和组织学特征与其食性的关系进行了探讨,旨在丰富塔里木裂腹鱼的生物学研究内容,可为其食性分析及饵料开发提供理论依据。     

褐菖鲉消化道的组织学和组织化学

褐菖鲉消化道的组织学和组织化学=Study on histology and histochemistry of digestive tract in Sebastiscus marmoratus[刊，中]/石戈（浙江海洋学院海洋科学学院，浙江 舟山 316004），王健鑫，刘雪珠，王日昕//水产学报.－2007，31（03）.－293～302 利用光镜技术对褐菖鲉消化道进行了组织学和组织化学研究。组织学研究表明：褐菖鲉消化道由口咽腔、食道、胃和肠4部分组成。口咽腔较大，上下颌，犁骨及腭骨均有细齿带,粘膜由复层鳞状上皮组成，并含有大量黏液细胞和少量杯状细胞；食道粗而短，上皮组织包括扁平上皮层区域和单层柱状上皮层区域，上皮含有大量杯状细胞和黏液分泌细胞，粘膜层的固有膜中含有腺体；胃呈Y型，包括贲门、胃体和幽门3个区域，胃粘膜由单层柱状上皮组成，在贲门和胃体部的粘膜层中有厚的结实层，上皮有大量的胃小凹和胃腺组织；胃幽门部括约肌明显，幽门上皮不含胃小凹；胃与肠相接处有8～9个指状幽门盲囊，其形态学和组织学特征与前肠类似；肠道上皮由单层柱状上皮细胞组成，丰富的微绒毛形成明显的纹状缘，上皮中含有大量杯状细胞，肠道系数为0.54。组织化学研究显示：幽门、幽门盲囊和肠上皮细胞顶端胞质和纹状缘具碱性磷酸酶活性；幽门盲囊及肠道上皮细胞顶端胞质中检测到酸性磷酸酶活性；在贲门部和胃体部的固有层以及幽门上皮还检测到酯酶活性，且酯酶定位于幽门柱状上皮细胞胞质的上半部。整个消化道的粘膜层中存在许多粘液细胞：食道上皮含大量酸性粘液细胞，胃上皮细胞均含有中性粘液，而肠道由前向后中性粘液物质逐渐减少，酸性粘液物质逐渐增多。组织学和组织化学的结果表明褐菖鲉食道有润滑和微弱的消化作用，胃有消化脂类和吸收糖类的功能；幽门和盲囊有较强的吸收脂类的功能；前肠、中肠和后肠有活跃的细胞内消化和吸收功能，整个消化道结构与其肉食性功能密切相关。图3参29     

凡纳滨对虾白便综合征的组织病理学观察

本文比较观察了不同规格的健康和患白便综合征凡纳滨对虾Litopenaeus vannamei肝胰腺、中肠、后肠、后盲囊等的组织结构。组织病理显示:白便综合征凡纳滨对虾肠道严重病变,肠腔空,环肌两侧增生大量成纤维细胞,这些增生细胞取代了肠上皮,而不见正常柱状上皮细胞;肝胰腺有不同程度和性质的病变,如腺管萎缩、崩解、坏死等。凡纳滨对虾患白便综合征的组织病变演变过程为:最初肠上皮基膜下出现一圈增生细胞,肠上皮柱状细胞脱离基膜;增生细胞持续增生增多,肠上皮崩解脱落至肠腔,增生细胞完全取代肠上皮;增生细胞不断增生,增生细胞层逐渐变厚,随着时间的推移,增生细胞层近腔端的一圈增生细胞坏死,出现一圈棕黄色物质,最终坏死细胞连同棕黄色物质脱落至肠腔。脱落至肠腔的腺管细胞、上皮细胞、增生细胞排出体外即为肉眼可见的白便。     

Supplemental effect of cholyltaurine and soybean lecithin to a soybean meal-based fish meal-free diet on hepatic and intestinal morphology of rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

The supplemental effects of cholyltaurine and soybean lecithin to a defatted soybean meal (SBM)-based fish meal-free diet on the hepatic and intestinal morphology of rainbow trout Oncorhynchus mykiss were investigated. A fish meal-based diet (FM), three fish meal-free diets supplemented either with soybean lecithin (SL), bovine gall powder (BG) or cholyltaurine (C-tau) and an unsupplemented fish meal-free diet (NFM), were given to fish (−11 g) for 10 weeks. The growth was the lowest in fish fed diet NFM, intermediate in fish fed diet SL and the highest in fish fed diet FM, BG and C-tau. Hepatocytes of fish fed diet NFM were atrophied, and the distal intestine of these fish showed abnormal features: disintegrated microvilli and fatty degeneration in epithelial cells and increased amount of connective tissue in the submucosa. Hepatic and intestinal histological features in fish fed diets SL, BG and C-tau were similar to those in fish fed diet FM. These results indicate that soybean lecithin, bovine bile salts and cholyltaurine have similar effects on normalizing the hepatic and intestinal morphologies of rainbow trout fed the SBM-based diet, although growth promotion effect was limited in the soybean lecithin.     

Changes in immune and enzyme histochemical phenotypes of cells in the intestinal mucosa of Atlantic salmon,Salmo salar L., with soybean meal‐induced enteritis

Extracted soybean meal (SBM) in the diet for Atlantic salmon, Salmo salar L., causes an inflammatory response in the distal intestine. The morphological changes of the epithelial cells and a characterization of the inflammatory cell infiltrate of the distal intestinal mucosa were studied using a panel of enzyme and immunohistochemical markers. The salmon (average body weight 927 g) used in the study were fed either a fishmeal‐based diet (control diet) or a diet in which 30% of the fishmeal protein was replaced with SBM protein (SBM diet). In salmon fed SBM, there were markedly reduced enzyme reactivities in the distal intestinal epithelial cells, both in the brush border [5′‐nucleotidase (5′N), Mg2+‐ATPase, alkaline phosphatase (ALP) and leucine aminopeptidase (LAP)] and in the intracellular structures [alkaline and acid phosphatase, non‐specific esterase (NSE) and alanine aminopeptidase (AAP)]. There appeared to be an increased presence of cells of monocytic lineage, including macrophages, as well as neutrophilic granulocytes and immunoglobulin (Ig) M in the lamina propria of the SBM‐fed fish. The mid intestine showed little response to the diet. The results suggest that toxic/antigenic component(s) of SBM affect the differentiation of the distal intestinal epithelial cells and may help explain the reduced nutrient digestibilities previously reported in salmonids fed extracted SBM.     

Histological and hormonal changes in the European eel (Anguilla anguilla) after exposure to environmental cocaine concentration

The aim of this study was the assessment of histological and hormonal changes induced in the European eel from environmental concentrations of cocaine. Silver eels were exposed to 20 ng L^?1 of cocaine during 50 days; at the same time, control, vehicle control and two post‐exposure recovery groups (3 and 10 days) were made. The general morphology of the skin and the intestine, and the plasma levels of prolactin, cortisol and dopamine were evaluated. In the skin, cocaine decreased the number and size of mucous cells, increased the thickness of the epidermis and altered the club cells and the basal lamina. In the intestine, cocaine increased the thickness of the epithelium and the number of mucous cells and reactivated the structure of the intestine and of the intestinal musculature. Moreover, cocaine increased plasma prolactin, cortisol and dopamine levels. These results suggest that cocaine induced histological changes, directly and/or through the hormonal changes observed. Considering the complex life cycle of the eel, the changes induced by cocaine in the skin, the intestine and the endocrine system could threaten the ability of the eel to successfully migrate and reproduce.     

Mast cells in the gills and intestines of naturally infected fish: evidence of migration and degranulation

Immunopathological and ultrastructural studies were carried out on the gills of bream, Abramis brama, naturally infected with the copepod Ergasilus sieboldi and on the intestine of brown trout, Salmo trutta, infected with the acanthocephalan Echinorhynchus truttae. Infected gills showed extensive tissue damage due to copepod attachment, including hyperplasia, as well as proliferation of mast cells, rodlet cells and mucous cells. In parasitized gills of bream, mast cells were more abundant than in uninfected gills. They were free within the lacunae, as well as outside and inside the blood vessels of the primary lamellae, and made intimate contact with vascular endothelial cells and with neutrophils. In some infected gills, degranulation of mast cells was common. Infected intestines of brown trout had more mast cells than uninfected intestines, and these cells were often in close proximity to, and inside, the capillaries and lying close to fibroblasts of the muscularis layer and stratum granulosum. Intense degranulation of mast cells was encountered in all intestinal layers, especially near the E. truttae body.     

Influence of certain soybean antinutritional factors supplemented to a casein-based semipurified diet on intestinal and liver morphology in fingerling rainbow trout <Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>

To investigate the cause of morphological changes occurring in the liver and intestine of rainbow trout Oncorhynchus mykiss fed defatted soybean meal (SBM)-based non-fish meal diets, morphological observations were conducted on fish fed casein-based semipurified diets supplemented with soybean antinutritional factors (soya saponin, soya isoflavone, soya lectin, oligosaccharide, Ca-phytate and their mixture). Hepatocytes and the epithelial cells in the hepatic ducts were not atrophied in any of the treatments. Lack of microvilli and pinocytotic vacuoles, and fatty degeneration of the epithelial cells were observed in the distal intestine of fish fed diets containing soya saponin. The proliferation of connective tissue in the mucosal folds and submucosa was shown in the distal intestine of fish fed the diet containing all substances including lectin. These results suggest that both saponin and lectin are the responsible factors in SBM for the occurrence of morphological changes of the distal intestine in rainbow trout fed SBM-based diets.     

Comparison of mudcrab‐based brackishwater polyculture systems with different finfish species combinations in Sundarban,India

To compare production and economic performance of polyculture systems with different species combinations, a 210‐day trial was carried out. In the first combination (T1), milkfish (Chanos chanos) and mudcrabs (Scylla serrata), and in the second (T2), mullets (Mugil cephalus, Liza tade and Liza parsia at 0.5:0.5:0.5 ratio) and mudcrabs were stocked keeping fish and mudcrabs at 15,000 numbers per ha, respectively, in both treatments. The finfish were fed floating pellet at 2%–3% and mudcrabs were fed fresh and farm made feed at 5%–8% body weight. Growth parameters of mudcrabs were similar in both T1 (407.64 ± 105.78 g) and T2 (418.89 ± 105.24 g), with no significant differences. Among finfish, M. cephalus attained highest final body weight, 241.55 ± 26.44 g followed by milkfish, 200.46 ± 11.82 g whereas lowest growth noticed in L. parsia (63.69 ± 6.62 g). Length–weight analysis of fish indicated negatively allometric growth (b < 3) for grey mullets, parsia and milkfish while L. tade recorded perfect cube low (b = 2.99). Male mudcrabs recorded positive allometric (b = 3.3) and female crab exhibited negative allometric growth (b = 2.68). The total productivity was 4,533 and 3,694 kg/ha with mudcrab contributes 53.69% and 60.56% to the total productivity in T1 and T2 respectively. The economic analysis indicated benefit–cost ratio (BCR) of 1.57 and 1.73 in T1 and T2 respectively with 10% and 35% insignificant increase (p > 0.05) in BCR and profit per kg, respectively, in T2 compared with T1. The study elucidates polyculture of mudcrabs with finfish can be a taken up as a profitable venture for sustainable diversification of brackishwater farming in Sundarbans.     

Bromodeoxyuridine DNA labelling reveals host and parasite proliferation in a fish‐myxozoan model

Enteromyxum leei is a myxozoan parasite responsible for enteritis in gilthead sea bream (Sparus aurata). The parasite proliferates in the paracellular space of the intestinal epithelium and induces an inflammatory reaction. To assess intestinal cell turnover and parasite proliferation, fish were infected with the parasite by anal intubation; after 17 and 64 days, the cell proliferative marker bromodeoxyuridine (BrdU) was administered; and after 24 hr, tissue samples were taken for immunohistochemical detection. Parasite exposure induced increased epithelial and immune cell proliferation in all intestinal segments at all time points, even before parasite establishment. This increased turnover was triggered early after intubation and mainly at a local level, as shown by an increased proliferating cell nuclear antigen (pcna) gene expression only at the posterior intestine after 17 days (not found in lymphohaematopoietic organs). Incorporation of BrdU in parasite secondary and tertiary daughter cells indicated that parasite endogeny is not by schizogonial division, which uses de novo synthesis pathway of pyrimidines. Altogether, BrdU immunolabelling and pcna gene expression showed the rapid proliferative response of the fish intestines upon a myxozoan infection and how this response is effectively triggered even before the parasite reaches or establishes in the site.     

Morphological characterization of the adherence and invasion of Streptococcus agalactiae to the intestinal mucosa of tilapia Oreochromis sp.: An in vitro model

Streptococcosis in tilapia Oreochromis sp. is possibly the most important bacterial disease for fish production worldwide. In Colombia, streptococcosis is caused by Streptococcus agalactiae (GBS), but in other countries, Streptococcus iniae is also involved. Prevention of streptococcosis is required and must be addressed for economic, social, international trade and public health reasons. This research used an in vitro culture of tilapia intestine to detail the intestinal mucosal response once the pathogen contacts the epithelium. We show that S. agalactiae sheds off its capsule to adhere to the epithelium. The bacterium adheres as a single individuum, in groups or in chains and is able to divide on the apical border of enterocytes. GBS adheres at and invades exclusively through the apical portion of the intestinal folds, using the transepithelial route. Once within the cytoplasm of enterocytes, the bacteria continue to divide. On the basolateral side of the epithelium, the microorganisms leave the cells to reach the propria and travel through the microcirculation. No evidence of an immuno‐inflammatory reaction or goblet cell response in the epithelium or the lamina propria was seen during the process of adherence and invasion of the pathogen.     

Colonisation tactics of three temperate catadromous species,eel Anguilla anguilla,mullet Liza ramada and flounder Plathychtys flesus,revealed by Bayesian multielemental otolith microchemistry approach

Daverat F, Martin J, Fablet R, Pécheyran C. Colonisation tactics of three temperate catadromous species, eel Anguilla anguilla, mullet Liza ramada and flounder Plathychtys flesus, revealed by Bayesian multielemental otolith microchemistry approach.
Ecology of Freshwater Fish 2011: 20: 42–51. © 2010 John Wiley & Sons A/S Abstract – The colonisation of Gironde (SW France) river catchment by juvenile, eel, Anguilla anguilla, flounder Platychtys flesus and thinlipp mullet Liza ramada was investigated comparatively using Sr:Ca and Ba:Ca composition of otolith. The relation between Sr, Ba and habitat was investigated based on Sr and Ba water composition sampled each month along the estuary‐river gradient. A total of 50 mullets, 30 eels and 47 flounders were collected in the Gironde river catchment. Analysis was performed with a Femtosecond LA‐ICPMS along a trajectory from the core to the edge. Sr and Ba water concentrations discriminated three habitats within the Gironde system, the lower estuary, the upper estuary and the freshwater sites. A signal processing method based on Gaussian hidden Markov models was applied to the multielemental life‐history data. The linear model used to allocate a Gironde habitat to coupled Sr, Ca values was parameterised with seasonal patterns and magnitude of Sr and Ba water values in the different habitats. The results showed that the three species used three different habitats and they had a large diversity of habitat use patterns with resident and nomadic tactics. Resident tactics were less frequent than nomadic tactics that suggested individual fish used two or more habitats. Mullet used a wider range of habitats in the lower part of the estuary than eel and flounder and switched habitats more frequently. Flounders tended to colonise initially freshwater, and then estuarine habitats later in life while mullets used the entire range of available catchment habitats throughout their life.     

Is the turbot,Scophthalmus maximus (L.), intestine a portal of entry for the fish pathogen Vibrio anguillarum?

The role of the intestinal tract in Vibrio anguillarum infection of turbot, Scophthalmus maximus (L.), fingerlings was investigated in two in vivo models and the possible mechanisms involved were studied in vitro. Viable V. anguillarum cells were detected in spleens from more than 50% of the fish administered the pathogen orally or rectally, suggesting that the intestinal tract is a portal of entry for V anguillarum. In transmission electron micrographs, V. anguillarum- like cells were seen close to the rectal epithelium, suggesting penetration of the mucus layer, but no epithelial cell penetration or endocytosis was evident. Attachment to intact turbot intestines was investigated, and 80% or more of the bacterial cells still remained attached after serial washings. A significantly higher number of cells attached to rectal segments than to the other intestinal segments. In vitro, V. anguillarum cells did not adhere specifically to intestinal mucus, but rather accumulated close to intestinal mucus interfaces and subsequently penetrated them. It is proposed that the intestinal ttact of tutbot is a portal of entry for V. anguillarum and that the cells penetrate the intestinal mucus overlaying the epithelial cells.     

The response of intestinal mucous cells to the presence of enteric helminths: their distribution,histochemistry and fine structure

Histochemical and ultrastructural investigations were conducted on the mucous cells of the intestine of brown trout, Salmo trutta L., naturally infected with the cestode Cyathocephalus truncatus (Pallas, 1781) and the acanthocephalan Echinorhynchus truttae Shrank, 1788. A subpopulation of 45 S. trutta were examined of which 15 specimens harboured E. truttae, 15 of which were infected with C. truncatus and 15 fish, the control group, were uninfected. In histological sections, hyperplasia and hypertrophy of the mucous cells were evident at the site of parasite infection. Enhanced mucus secretion was also recorded in infected fish. The number of mucous cells close to the site of parasite attachment within the intestine was significantly higher than the number detected in uninfected individuals and in infected individuals at sites 1 cm or greater from the point of parasite attachment. There were no significant differences between the number of mucous cells found at the latter two sites. Alcian blue and periodic acid‐Schiff’s staining of representative histological sections revealed a significant increase in the number of mucous cells staining positively for acid glycoconjugates compared to the number of cells found in the intestines of uninfected S. trutta. In transmission electron microscopy sections, each mucous cell typically possessed an elongated, basally positioned nucleus. The cytoplasm was observed to possess numerous electron dense and lucent vesicles, in addition to well‐developed rough endoplasmic reticulum, Golgi apparatus and a few round mitochondria.     

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.