Morphological study of the gastrointestinal tract of Larimichthys crocea (Acanthopterygii: Perciformes)

Morphofunctional analysis of the gastrointestinal tract of an annual killifish: In search of structural traits related to the annual life history

Annual killifishes have active and voracious rates in acquisition of food resources with display of behaviors that allow them to maintain high metabolic rates to deal with the harsh and unpredictable conditions prevalent in temporary pools where they inhabit. The objective of this research was to describe histologically and ultrastructurally, the digestive system of the annual killifish Millerichthys robustus to identify morphological traits related to its annual life history and digestive physiology. Also, we quantify food items along the intestine as a proxy for rates of digestion. Millerichthys has a short digestive system, associated with a carnivorous diet, with no evidence of a stomach. Instead, the presence of pharyngeal jaws with caniform teeth was documented, related to the breakdown of invertebrate exoskeletons, allowing prey fluids to be tasted by taste corpuscles related to selection of food items, and that digestive enzymes penetrate once in the intestine. The histological morphology of the intestine showed four different regions, associated with its digestive rates: (i) reception of food from the esophagus with intact pray; (ii) digestion with enzymes from the pancreas and liver/gallbladder of simple exoskeleton prey (Entognatha), and beginning of absorption; (iii) absorption of nutrients, and digestion of large-complex exoskeleton prey (Hexanauplia, Brachiopoda, and Ostracoda); and (iv) probable absorption of intact macromolecules. The second region of the intestine presented two anatomical loops and the highest thickness that may be related to reducing the speed of food transit, allowing for more efficient digestion given the large amount of food ingested by this species.

Comparative digestive biology between the ponyfishes from the Pranburi River estuary, Thailand

We investigated the digestive biology of two prevalent leiognathid species in Pranburi River estuary, Thailand: the decorated ponyfish (Nuchequula gerreoides) and the splendid polyfish (Eubleekeria splendens). A total of 632 samples collected from February to April and September to November 2017 were analysed using morphological and histological approaches. The overall structures were similar between the species: a short mucous-cell-rich oesophagus region, a well-developed gastric gland uniformly present across the stomach's mucosal layer, and three finger-like pyloric caeca between the stomach and intestine. However, there were marked differences in the mouth, gill raker, and intestinal coefficient (IC). N. gerreoides had a relatively longer mouth, smoother gill rakers, and an IC of 1.08 ± 0.01, similar to those of other carnivorous fish. In contrast, the gill raker of E. splendens had more villiform teeth that can filter-feed better, and their IC was 2.16 ± 0.02 (i.e., longer intestine). Although digestive structures were generally similar between the ponyfishes, these differences suggest that N. gerreoides is relatively carnivorous with stronger suction, whereas E. splendens may be an omnivorous or herbivorous filter-feeder.

Prenatal developmental sequences of the esophageal epithelium in the New Zealand white rabbits: Light and electron microscopic analysis

Several morphogenetic sequences occur during esophageal development and birth defects occur due to defects in foregut morphogenesis. This work aimed to record the cellular events in the morphogenesis of rabbits' esophageal epithelium. On the 16th day of gestation, the esophageal epithelium varied from stratified ciliated columnar to stratified squamous type. The surface epithelium presented mucous cells with mucigen granules of various sizes occupying their supranuclear cytoplasm. Cytoplasmic vacuolation was evident in all layers of the esophageal epithelium at this age. On the 18th gestational day, some light cells could be detected in the middle portion of the epithelium, while others occupied the whole epithelial length. On the 21st day, mucous cells are more frequently observed at the apical esophageal part as well as at the surface epithelium. Numerous elongated dark cells could be distinguished embedded between the basal cells. On the 24th gestational day the number of the mucous cells reached its peak. Reaching the 30th gestational day, several lamellar bodies, a keratinized layer and mitotic divisions could be demonstrated, and the number of both mucous and dark cells was greatly decreased. Collectively, detection of surface mucous and dark cells together with the non-cornified surface in some regions of the rabbit esophageal epithelium at the end of gestation ensure a postnatal development to reach the adult epithelium essential to sustain the passage of the harsh raw food. Future immunohistochemical studies are recommended to investigate the components of secretions in mucous cells and functional studies to highlight the dark cells significance. RESEARCH HIGHLIGHTS: Esophageal epithelium of fetal rabbit was analyzed by light and transmission microscopy. Surface epithelium presented mucous cells with mucigen granules of various sizes. They reached their maximum number on 24th day then decreased. On the 16th day, cytoplasmic vacuolation was evident in all epithelial layers. On the 21st day, numerous elongated dark cells could be distinguished embedded between the basal cells. Before birth, several lamellar bodies, a keratinized layer and mitotic divisions could be demonstrated, and the number of both mucous and dark cells was greatly decreased.

Histomorphological Changes in Fish Gut in Response to Prebiotics and Probiotics Treatment to Improve Their Health Status: A Review

The gastrointestinal tract (GIT) promotes the digestion and absorption of feeds, in addition to the excretion of waste products of digestion. In fish, the GIT is divided into four regions, the headgut, foregut, midgut, and hindgut, to which glands and lymphoid tissues are associated to release digestive enzymes and molecules involved in the immune response and control of host-pathogens. The GIT is inhabited by different species of resident microorganisms, the microbiota, which have co-evolved with the host in a symbiotic relationship and are responsible for metabolic benefits and counteracting pathogen infection. There is a strict connection between a fish's gut microbiota and its health status. This review focuses on the modulation of fish microbiota by feed additives based on prebiotics and probiotics as a feasible strategy to improve fish health status and gut efficiency, mitigate emerging diseases, and maximize rearing and growth performance. Furthermore, the use of histological assays as a valid tool for fish welfare assessment is also discussed, and insights on nutrient absorptive capacity and responsiveness to pathogens in fish by gut morphological endpoints are provided. Overall, the literature reviewed emphasizes the complex interactions between microorganisms and host fish, shedding light on the beneficial use of prebiotics and probiotics in the aquaculture sector, with the potential to provide directions for future research.

Morphology, Histology, and Histochemistry of the Digestive Tract of the Marbled Flounder Pseudopleuronectes yokohamae

This study investigated the morphological, histological, and histochemical characteristics of the digestive tract of the marbled flounder (Pseudopleuronectes yokohamae). The relative length of the gut of the marbled flounder digestive tract was 1.54 ± 0.10 (n = 20), and it had a simple stomach and 6-9 pyloric caeca. The mucosal folds of the marbled flounder digestive tract exhibited a general branched morphology. The thickness and mucosal fold length of the intestinal muscularis externa showed similar aspects in all areas. The thickness of the intestinal muscularis externa was the thickest in the posterior intestine portion, and the length of mucosal folds was the longest in the anterior intestine portion. It was indicated that food digested by gastric acid in the stomach moves to the anterior portion (including pyloric caeca) and mid portion of the intestine, ensuring effective stimulation of cholecystokinin (CCK)-producing cells. In addition, the distribution pattern of CCK-producing cells in the intestine was very similar to that of mucus-secreting goblet cells. The CCK-producing cells and goblet cells in the marbled flounder were well-adapted to promote optimal control of the digestive process. Based on the morphological and histochemical studies, it was concluded that the marbled flounder displays a digestive tract comparable to that of fish species with carnivorous habits.

Intestinal morphometry and cell density features in tropical farmed fish: A methodological approach

The digestive tract of fish has many morphological adaptations related to habitat and nutrition. Intestinal biometry may reflect these adaptations. Here, we aimed to describe histometric patterns in farmed fish and their relationship with feeding by using a standardized protocol considering cell density by tissue area. Five juvenile specimens of each species (Pseudoplatystoma corruscans, Piaractus mesopotamicus, and Oreochromis niloticus) were used. O. niloticus possessed higher intestinal weight and length besides higher intestinal quotient and intestinal somatic index than the other species. The general histological composition was similar between species. However, P. corruscans showed differences in thickness between the anterior and posterior segments. O. niloticus had thinner serosa and muscularis layers than the other species. The cell density was distinct in both species and segments. Comparing the intestinal segments, O. niloticus displayed the lowest count of granulocytes. Goblet cell density was lower in P. mesopotamicus in all segments. However, the volume of these cells was higher in the anterior and middle anterior segments. Our data demonstrated that intestinal structural plasticity is associated with the difference in feeding habits. Here, we used quantitative standardized histometric criteria to understand the morphophysiological diversity of the fish digestive tract, and this technique can be applied in future studies to evaluate changes in the digestive tracts of vertebrates.

Prejuveniles of Mugil liza (Actinopterygii; Fam. Mugilidae) show digestive and metabolic flexibility upon different postprandial times and refeeding

Many animals face periods of feeding restrictions implying fasting and refeeding. The determination of digestive/metabolic and body condition parameters at different times of food deprivation and after refeeding allows to evaluate the postprandial dynamics, the transition from feeding to fasting and the capacity to reverse digestive and metabolic alterations. In spite of its physiological importance, studies on estuarine-dependent detritivore fish are lacking. We determined total mass (TM), relative intestine length (RIL), hepatosomatic index (HSI), digestive enzymes activities in the intestine and energy reserves in liver and muscle at 0, 24, 72, 144 and 240 h after feeding and at 72 h after refeeding in prejuveniles of Mugil liza (Mugilidae) as a model species. After feeding, a decrease occurred in: TM (144 h, 25%), RIL (144 h, 23%); amylase and maltase (72 h, 45 and 35%), sucrase (24 h, 40%) and lipase (24 h, 70%) in intestine; glycogen and free glucose (72 h, 90 and 92%) in liver. In muscle, glycogen (72-144 h) and free glucose (144 h) (170% and 165%, respectively) peak increased; triglycerides decreased at 24-240 h (50%). After refeeding TM, RIL, carbohydrases activities in intestine, glycogen and free glucose in liver were recovered. In muscle, glycogen and free glucose were similar to 0 h; lipase activity and triglycerides were not recovered. Trypsin and APN in intestine, triglycerides in liver, protein in liver and muscle and HSI did not change. The differential modulation of key components of carbohydrates and lipid metabolism after feeding/refeeding would allow to face fasting and recover body condition. Our results improve lacking knowledge about digestive and metabolic physiology of detritivore fish.

Evaluation of secretory activity in carp pancreatocytes (Cyprinus carpio L.) when using lactobacillus-based chelate and probiotic supplemental feed complexes

The experimental research was carried out on the juvenile carp (Cyprinus carpio L.). The impact from supplemental feeds consisting of variable concentrations of chelate compounds, biogenic trace elements and probiotic lactobacillus-based product Bacillus subtilis VKPM B-2335 was evaluated. Optical and qualitative parameters of the lactobacillus base were studied in order to identify the major group of substances potentially able to influence the end result. The purpose of this research was to identify changes in the structure of the zymogen granules and their dimensions at which supplemental feeds produce a stimulating effect on the synthesis of zymogens in exogenous cells of the secretory part of pancreas. At the outcome of the study, for the first time, it was possible to prove that the integrated action of chelates and lactobacillus-based probiotics complemented each other. Metal chelate compounds contributed to enlargement of the zymogen granules, if compared to the control values. The bacterial products accelerated production of the zymogen granules in acinar cells diffusely located in carp hepatopancreas.

Can a biopesticide based on Bacillus thuringiensis affect the physiology and histomorphology of Arapaima gigas?

The use of biopesticides based on Bacillus thuringiensis (Berliner 1915) in agriculture has been considered harmless for non-target organisms such as fish. The present study aimed to investigate the effects of a biopesticide based on B. thuringiensis on the physiology and histology of the liver, kidney and intestine of Arapaima gigas (Schinz, 1822), via exposure to water (0.13 g/L) and in the diet (0.13 g), after 24 and 48 h. Fish subjected to B. thuringiensis in the water of their breeding and feeding tanks exhibited mortality due to changes in erythrogram (hematocrit, hemoglobin, erythrocytes), thrombogram and leucogram blood parameters, and plasma (sodium, chloride, potassium, cholesterol, glucose, triglycerides, cortisol and total proteins) and enzymatic (Aspartate Amino Transferase and Alanine Amino Transferase) biochemistry. Histopathological alterations in the liver and kidney ranged from mild to severe and were characterized by the presence of cytoplasmic vacuolization, nuclear hypertrophy and atrophy, melanomacrophage centers and necrosis, and in the intestine by changes to the number of villi and goblet cells. Therefore, these physiological and histopathological alterations indicate that care should be taken with the dispersion of biopesticides based on agricultural B. thuringiensis in fish farming.

Digestive tube of an herbivorous fish (Rhytiodus microlepis) from the Amazonian floodplain lakes: A morphological and histochemical study

This study describes the morphology and histochemistry of the digestive tube of the herbivorous fish Rhytiodus microlepis, which is commonly found in the Amazonian floodplain lakes, Brazil. Thirty-eight fish were used in this study. The digestive tube was measured and dissected for anatomical description, and stained with (i) haematoxylin and eosin, for histological analyses; (ii) periodic acid-Schiff, for detected neutral mucins; and (iii) Alcian Blue (AB) pH 1.0 and 2.5 for acid and sulphated acid mucins. The oesophagus, with its secretory cells and taste buds, is adapted for lubrication of vegetable matter, resistance to friction and reception of stimuli. The stomach is U-shaped and rich in gastric glands, particularly in cardiac and fundic regions, which are adapted to receive large amounts of food, and promotes the digestion. The intestine comprises more than 70% of the digestive tube. All portions of the intestine, except the rectum, have the same pattern of mucosal folds, and the goblet cells reacted positively to all histochemical methods (PAS, AB 1.0 and 2.5), while rodlet cells reacted only to periodic acid-Schiff (PAS) staining. Neutral mucins and sulphated acid mucins predominated in the anterior portion of the intestine and a high concentration of carboxylated acid mucosubstances were present in the other portions. The rectum showed a strong reaction to all histochemical methods. The muscular layer of the intestine consists of three layers, which showed features presumably related to the rigid nature of the food. A simple squamous epithelium constitutes the serous layer over the entire length of the tube.

Developmental events and cellular changes occurred during esophageal development of quail embryos

The current study focused on the histogenesis of the esophagus in quail embryos. Formation of the gut tube occurred on the 4th day of incubation. Development of the muscular layers occurred in a sequential manner; the inner circular layer on the 7th day, the outer longitudinal layer on the 8th day and the muscularis mucosae on the 9th day. Glandular development began on the 13th day of incubation. The epithelium was pseudostratified columnar that consisted of mucous cells, dendritic cells, and keratinocyte precursors. Epithelial stratification occurred on the 15th day of incubation. We used Mallory trichrome, Weigert-Van Gieson, and Gomori silver stains to visualize fibrous components. Scanned samples showed formation of endoderm and mesoderm on the 5th day of incubation. A layer of myoblasts developed on the 8th day of incubation. Formation of mucosal folds, which contained glandular openings, occurred on the 14th to 17th days of incubation. On the 5th to 8th days of incubation, CD34 and vascular endothelial growth factor (VEGF) positive-mesodermal cells, and telocytes (TCs) were detected. On the 15th day of incubation, CD34 and VEGF positive-telocytes, and fibroblasts, were identified. The current study described the correlations between functional morphology and evolutionary biology.

Description of the unusual digestive tract of Platax orbicularis and the potential impact of Tenacibaculum maritimum infection

Background

Ephippidae fish are characterized by a discoid shape with a very small visceral cavity. Among them Platax orbicularis has a high economic potential due to its flesh quality and flesh to carcass ratio. Nonetheless, the development of its aquaculture is limited by high mortality rates, especially due to Tenacibaculum maritimum infection, occurring one to three weeks after the transfer of fishes from bio-secure land-based aquaculture system to the lagoon cages for growth. Among the lines of defense against this microbial infection, the gastrointestinal tract (GIT) is less studied. The knowledge about the morphofunctional anatomy of this organ in P. orbicularis is still scarce. Therefore, the aims of this study are to characterize the GIT in non-infected P. orbicularis juveniles to then investigate the impact of T. maritimum on this multifunctional organ.

Methods

In the first place, the morpho-anatomy of the GIT in non-infected individuals was characterized using various histological techniques. Then, infected individuals, experimentally challenged by T. maritimum were analysed and compared to the previously established GIT reference.

Results

The overlapped shape of the GIT of P. orbicularis is probably due to its constrained compaction in a narrow visceral cavity. Firstly, the GIT was divided into 10 sections, from the esophagus to the rectum. For each section, the structure of the walls was characterized, with a focus on mucus secretions and the presence of the Na⁺/K⁺ ATPase pump. An identification key allowing the characterization of the GIT sections using in toto histology is given. Secondly, individuals challenged with T. maritimum exhibited differences in mucus type and proportion and, modifications in the mucosal and muscle layers. These changes could induce an imbalance in the trade-off between the GIT functions which may be in favour of protection and immunity to the disadvantage of nutrition capacities.

Development of the digestive system of Argentine hake, Merluccius hubbsi, larvae

The Argentine hake Merluccius hubbsi is an important fishery resource of the Southwestern Atlantic Ocean and it is also a potential species for cultivation. In this work, the digestive system development in field-caught hake larvae was studied using histological and histochemical approaches. The digestive tract of larvae was divided into: oropharyngeal cavity (OPC), esophagus, stomach (that develops in the preflexion stage), and intestine. The annexed digestive glands consisted of the liver and the exocrine pancreas. At the beginning of the preflexion stage, teeth were developed in the OPC. There were mucous cells in the esophagus secreting different glycoconjugates from hatching. The enterocytes in the posterior intestine exhibited supranuclear vesicles associated with protein absorption. Mucous cells were observed in the posterior intestine in the preflexion stage and, in the anterior region, ending the flexion stage. Each type of glycoconjugates has a specific role. Acidic mucins lubricate and protect from mechanical damage, sialomucines protect from bacterial infections and neutral mucins regulate the acidity of mucus secretion, protect against abrasion and participate in the formation of the chyme, indicating a pregastric digestion. The liver was present since hatching with pancreatic tissue inside and increased in size acquiring the typical structure with hepatocyte cords, sinusoids, vacuoles, and hepatic duct. The hepatocytes vacuolization increased with larval development. The pancreas became extra-hepatic, with basophilic acinar cells and acidophilic zymogen granules. Throughout the ontogeny, the increased structural and functional complexity of the digestive system reflected the transition to exogenous feeding and nutritional increasing needs.

Morphological and histochemical characterisation of the mucosa of the digestive tract in matrinxã Brycon amazonicus (Teleostei: Characiformes)

This study describes anatomical, histological and histochemical features of the digestive tract mucosal layer of the matrinxã Brycon amazonicus, an omnivorous freshwater fish endemic from the Amazon basin. This species presents short thick oesophagus with longitudinal folds, that allow the passage of large food items. The mucosa is lined with a stratified secretory epithelium rich in goblet cells that secrete neutral and acid mucins. The two mucin types provide different viscosity in anterior and posterior oesophagus related to the protective and lubricant functions, respectively. The stomach is a highly distensible Y-shaped saccular organ. Here, it is proposed that this anatomical shape plays an essential role in food storage when food availability is abundant. The stomach mucosa is composed of epithelial cells with intense neutral mucin secretion to protects against gastric juice. The intestine is slightly coiled and presents internally a complex pattern of transversal folds that increases the absorption surface and the retention time of food. Goblet cells in the intestine secrete acid and neutral mucins that lubricate the epithelium and aid in the digestive processes. In the rectum, an increase in goblet cells population occurs that may be related to better lubrication.

Morphological study of the gastrointestinal tract of the snow trout, Schizothorax esocinus (Actinopterygii: Cypriniformes)

The present study aimed to investigate the macroscopic structure of the gastrointestinal tract (GIT) of Schizothorax esocinus Heckel, 1838. The surface architecture of the buccopharynx, oesophagus and the entire intestinal tract of S. esocinus has been examined under scanning electron microscope (SEM) after fixing in 2.5% glutaraldehyde buffered with 0.1 M sodium cacodylate at pH 7.3 for 18–48 hours and post-fixation for two hours at room temperature in 1% osmium tetra oxide buffered at pH 7.3 with 0.1 M cacodylate. The mucosal surface of buccopharynx, esophagus, intestinal bulb, and intestine reveal prominent longitudinal major or primary mucosal folds which are further subdivided into the series of irregular and well-circumscribed folds called minor or secondary folds. However, in the intestinal bulb and intestine, the longitudinal major or primary folds themselves form wavy or zigzagging patterns along the mucosal surface. The fine structure of the surface epithelium further shows that the apical surfaces of the epithelial cells are ped with finger-print like microridges, arranged in various patterns and regularly spaced. The rectal mucosa, on the other hand, displays a highly irregular type of major mucosal folds. The separation can’t be seen between major mucosal folds. A thin film of mucous spread over the mucosal folds and the numerous pores through which mucous cells release their content has also been noted along the rectal mucosa. This investigation suggests the possible role of different digestive organs in relation to feeding, digestion, storage, absorption, and various other physiological processes, thereby providing a knowledge necessary to the understanding of pathological or physiological alterations in both aquaculture and natural environment.