Microscopic morphology and histochemistry of the digestive system of a tropical freshwater fish Trichomycterus brasiliensis (Lütken) (Siluroidei, Trichomycteridae)

Histological structure of the digestive tract, liver, and pancreas of Ambassis nalua (Hamilton, 1822) with ultrastructural details of the gastric gland

The scalloped perchlet Ambassis nalua is one of the dominant fishes in the Estuarine Pranburi River, Thailand. It is suggested that this fish is in the secondary trophic level with a carnivorous nature. Studies on digestive system will help us further identify the niche of this species in the food web/food chain. The present study therefore aimed to report the detailed structure and ultrastructure of A. nalua digestive system. Fish samples (n = 30) with a total length of 5.7 ± 0.5 cm were obtained using beach seines from the Estuarine Pranburi River. Their digestive tract length and intestine coeficient were 3.6 ± 0.07 cm and 0.91, respectively. Light microscopic observation showed that the digestive wall comprised four layers, namely mucosa, submucosa, muscularis, and serosa. The prominent mucous-secreting cells were found in the mucosal oesophagus. The stomach had many gastric folds, with height and width being 649.76 ± 85.15 and 370.30 ± 68.56 μm, respectively. Gastric glands were found in the anterior stomach but not in the posterior stomach. Each gastric gland was made up of a single type of columnar cells. The gastric cells were ultrastructurally characterized by numerous mitochondria and well-developed secretory granules of varying sizes. A few small vacuoles were also identified in the apical area of the gastric cells. The intestine had two regions (anterior and posterior intestines), and pyloric caecum was absent. The density of the goblet cell was significantly higher in the posterior intestine. These results provide basic knowledge of the digestive system of A. nalua, and the low intestine coefficient and the absence of pyloric caecum suggest the carnivorous feeding habit of this species.

Anatomy of the endocrine pancreas in actinopterygian fishes and its phylogenetic implications

The anatomy and organisation of the endocrine pancreas in ray-finned fishes vary widely. The two main morphoanatomical character states are diffuse versus compact pancreatic tissue. The latter are called Brockmann Bodies (BBs), or principal islets. The present study is the first comprehensive survey on the anatomy of the endocrine pancreas (diffuse versus compact) across 322 actinopterygian species in 39 orders and 135 families based on literature, specimen dissections, and Magnetic Resonance Imaging (MRI). The data obtained show that large endocrine pancreatic islets (BB) have appeared several times in teleost evolution: in some ostariophysian clades and within the Salmoniformes and Neoteleostei. Acanthomorpha (spiny-rayed fishes) is the largest clade of the Neoteleostei. Within this clade, an absence of BBs is only observed in flying fishes (Exocoetidae), parrotfishes (Scarinae), and some of the scarine relatives, the Labridae. The presence of BBs in examined jellynose fish species from the Ateleopodiformes indicates support for its sister-group relationship to the Ctenosquamata (Myctophiformes + Acanthomorpha). More investigations are still needed to corroborate the presence or absence of BBs as a putative synapomorphy for a clade comprising Ateleopodiformes and Ctenosquamata.

A Morphological and Ultrastructural Study of the Anterior Digestive Tract of Adult Nile Tilapia Oreochromis niloticus

Among the most-used fish species in aquaculture is the Nile tilapia, due to its rapid growth rate and its adaptation to a wide range of farming conditions. A careful description of the morphology of the digestive tract, particularly the esophagus and stomach, allows a better understanding of the relationship between structure and function. Combining scanning and light microscopy we highlighted the presence of five different zones in the stomach (1: esophagus-gastric lumen passage; 2: descending glandular portion; 3: fundic portion; 4: ascending glandular portion; 5: gastric-pyloric transition portion). Histochemical investigation showed a secretion of carboxylates mucopolysaccharides along the esophagus and sulphated complex carbohydrates in the stomach. These results suggest that mucins play a protective role of the epithelial lining, which is essential for a correct digestive process. Finally, the characterization of the main cellular structures may be inspiring for more advanced studies aiming to decipher the role of specific molecules, such as neuropeptides, involved in the physiological digestive process.

Morphological study of the digestive tract of the cardinal tetra, Paracheirodon axelrodi (Characiformes: Characidae)

Abstract The cardinal tetra Paracheirodon axelrodi is a species of the family Characidae of great interest as an ornamental fish. Many aspects of the biology of this species are still unknown. The present work presents a complete description of the different components of the digestive tract of P. axelrodi, analyzing its global anatomical arrangement, the adjacent glands (liver and pancreas) and the previously ignored pyloric caeca, using histological and histochemical techniques with light microscopy and scanning electron microscopy. Three levels of analysis were performed: macroscopic anatomy, histology of the gastrointestinal tract and scanning electron microscopy of mucosal surfaces. The intestinal coefficient (Ci) of P. axelrodi calculated here (0.94) is within the expected range for a carnivorous species. The anatomy of the alimentary and the resulting Ci is consistent with carnivorous diet in line with dietary studies in the wild in this species. The digestive tract, including adjacent glands (liver and pancreas), presented a relatively conserved general pattern within that described for other species of the family Characidae, especially at the histological level.

Morphological and histochemical features of the digestive tract of Leiarius marmoratus (Gill, 1870)

Leiarius marmoratus, a freshwater catfish from Pimelodidae family, shows great biological and commercial relevance because of its geographic distribution and adaptation to fish-farm. The knowledge of the morphological characteristics of the digestive tract is fundamental to the understanding of fish physiology and nutrition, which helps in the planning of diets to provide better management and success in fish farming. Thus, this work described the morphology and histochemistry of the digestive tract of L. marmoratus adults. After euthanasia, the animals were dissected for analysis of the digestive tract. The oesophagus is a short and distensive organ with longitudinal folds that allow the passage of large food, e.g., other fishes. Oesophageal mucosa layer shows a stratified epithelium with goblet cells and club cells. The secretion of goblet cells is composed of neutral and acidic mucins that are anchored in the epithelium luminal face by epithelial cells fingerprint-like microridges, lubricating the surface to facilitate the food sliding. Club cells have protein secretion that can be involved in alarm signals when epithelium is damaged and in immunological defence. The saccular stomach is highly distensible to store large food. Gastric mucosa layer is composed of epithelial cells with intense secretion of neutral mucin to protect against self-digestion of gastric juice. Cardiac and fundic regions of stomach show well-developed gastric glands composed of oxynticopeptic cells. These cells have numerous mitochondria, highlighting their intense activity in the synthesis of acid and enzymes. The intestine is divided into three regions: anterior, middle and posterior. Although it is a short tube, intestine shows longitudinal folds and microvilli of enterocytes to increase the contact surface. These folds are higher in the anterior region of the intestine, highlighting their function in digestion and absorption. Intestinal goblet cells have acidic and neutral mucins that lubricate the epithelium and aid in digestive processes. These cells increase in number towards aboral, and they are related to the protection and lubrication to expulsion of faecal bolus.

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.

Preliminary Assessment on the Histological Changes in Juvenile Siganus guttattus (Bloch, 1787) Exposed to Plastic Debris

Plastic debris is ubiquitous in the marine environment and many of this is polyethylene based plastic bags. Its potential effect on marine organisms is still understudied. Hence, this study determined the histological changes induced in the intestine and liver of the juvenile rabbit fish, Siganus guttatus. S. guttatus (N = 150) were sub chronically exposed to plastic bag debris suspensions (0, 0.01, 0.1, 1.0 and 10 mg L^-1) for 10 days. In addition to histological changes, the condition factor (CF) index of the fishes were assessed. Results showed that there was no significant difference in the CF index of the fishes exposed to varying concentrations of plastic suspensions, there was however histological changes in fishes exposed to 10 mg L^-1. The histological changes in the intestine were hyperemia, necrosis, goblet cells hyperplasia, and shortening of the villi. Histological changes in the liver were hyperemic blood vessels and vacuolization. Fishes exposed to 10 mg L^-1 exhibited a higher proximal, distal, liver and total organ index as compared to those unexposed (p < 0.05).

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.

Morphology, histology and histochemistry of the digestive tract of the Banded tilapia, Tilapia sparrmanii (Perciformes: Cichlidae)

This study described anatomical, histological and histochemical features of the mucosal layer of the digestive tract of Tilapia sparrmanii Smith, 1840, an omnivorous freshwater fish endemic to Southern Africa. This species exhibited a short thick oesophagus with long deep longitudinal folds (466.68 ± 16.91 µm), and a thick (173.50 ± 10.92 µm) muscular layer that allow the passage of large food items. The mucosa was lined with stratified secretory epithelium rich in goblet cells that secreted neutral and acid mucins. The stomach was a sac-like structure with simple tubular glands surrounded by connective tissue. The mucosa was lined with simple columnar epithelium and the lamina propria exhibited a well-developed layer of gastric glands that occupied the entire length of the cardio-fundic region. The stomach mucosa consisted of epithelial cells with intense neutral mucin secretion which protects against gastric juice. Neck cells of gastric glands synthesized neutral and acid mucins. The intestine was highly coiled and presented a complex pattern of transversal folds internally (villi). Villi length decreased progressively from the anterior to the posterior intestine (p &lt; 0.0001). Tunica muscularis of the mid-intestine had the thinnest thickness among all parts of the intestine (p &lt; 0.0001). Goblet cells whose numbers increased towards the rectum secreted both acid and neutral mucins. The results indicate structural similarities of T. sparrmaniiGIT with other tilapia species and will be useful for understanding the physiology of the digestive systems as well as functional components of the GIT.

Ontogeny of the digestive tract of Brycon amazonicus (Teleostei, Bryconidae) under culture conditions: from hatching to juvenile stage

In the present study, the morphological development of the Brycon amazonicus digestive tract is described to provide basic knowledge for nutritional studies and, therefore, increase the survival of this species during larviculture. Samples were collected from hatching up to 25 days of age, measured, processed and observed under a stereomicroscope and light microscopy. Newly hatched larvae presented their digestive tract as a straight tube, dorsal to the yolk sac, lined with a single layer of undifferentiated cells. At 24 h post-hatching (hPH), the buccopharyngeal cavity was open, but the posterior region of the digestive tube remained closed. At 25 hPH, the digestive tube was completely open and could be divided into buccopharyngeal cavity, oesophagus and intestine. At 35 hPH, the intestine presented a dilatation in the proximal region, which had the function of storing food. Differentiation of the stomach started at 83 hPH, and mucous cells were observed in the epithelium. These cells are important in the production of mucus, whose function is to protect the organ against acidity, although the gastric glands began developing only from 171 hPH, when three stomach regions were observed: cardiac, fundic and pyloric. The gastric glands were observed in the cardiac region, indicating that this organ already had digestive functionality. From 243 hPH, the absorption and assimilation of nutrients were already possible but, only from 412 hPH, the digestive tract was completely developed and functional.

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 Larimichthys crocea (Acanthopterygii: Perciformes)

The present study aimed to investigate the macroscopic and histological structure of the gastrointestinal tract (GIT) of Larimichthyscrocea (Richardson, 1846). It consists of esophagus, stomach regions, pyloric caeca, intestinal regions, and rectum. Sixteen tubular light yellowish pyloric caeca of similar sizes were observed in all individuals. The digestive wall consists of mucosa, submucosa, muscularis, and adventitia. No major differences appeared in the structure of the tunica, epithelial cell types, connective tissues and musculature glands of L.crocea GIT. The mucosal epithelia in the oesophagus has longitudinal branched folds with frontward and hindmost zones. The gastric tunica mucosa has a characteristic folded structure and can be divided into three regions. The intestinal tunica mucosa is characterized by villi structures and numerous mucus-secreting cells. Mucus-secreting goblet cells were strongly positive to AB at pH 2.5 in the oesophagus (excluding gastro-oesophageal junction) and intestine mucosal regions, which indicates an abundance of carboxylate mucins. The surface epithelia of the gastric mucosa is PAS-positive and AB-negative. SEM examination revealed that cells in the epithelium of the esophagus have an unbroken apical layer and goblet cells. The intestinal coefficient (IC) of L.crocea was 0.80 ± 0.21, consistent with a carnivorous or omnivorous habit. Our study adds the knowledge of the digestive system of L.crocea and might be useful in the management of L.crocea stocks.

Structure of the alimentary tract in the Atlantic mudskipper Periophthalmus barbarus (Gobiidae: Oxudercinae): anatomical, histological and ultrastructural studies

The alimentary tract of oxudercine gobies is characterized by a lack of an anatomically distinct stomach, owing to which they are classified as stomachless. Since the environment, food requirements, and feeding habits have a significant impact on the anatomy of the alimentary tract of fish, it was assumed that predominantly carnivorous, semi-terrestrial mudskippers would have a stomach. In order to verify this hypothesis, anatomical, histological, histochemical and ultrastructural analysis of the alimentary tract of the Atlantic mudskipper Periophthalmus barbarus was performed. The results revealed that despite a lack of clear anatomical distinction within the alimentary tract, there were four well-distinguished sections visible at the histological level: oesophagus, stomach, intestine, and rectum. The division was enhanced by the presence of a pyloric sphincter and an ileorectal valve. The stomach contained tubular glands composed of oxynticopeptic cells. Gland cells had pepsinogen granules and a well-developed tubulovesicular network of smooth membranes, which indicates the secretion of gastric juice. The presence of neutral mucus in the apical region of surface epithelial cells as protection against hydrochloric acid as well as the presence of active pepsin also confirm gastric function. However, low pepsin activity seems to implies low protein digestion. The results of this study indicate that the Atlantic mudskipper P. barbarus has a functional stomach.

Histomorphological Description of the Digestive System of Pebbly Fish, Alestes baremoze (Joannis, 1835)

Histomorphological studies of the digestive system of Alestes baremoze captured from Lake Albert, Uganda, were done using standard procedures. These revealed that A. baremoze has a fleshy-lipped terminal small mouth, large molar, short oesophagus, a three-lobed liver, pouch-like stomach, a nine-fingered caeca, and a long tubular intestine. A stratified squamous epithelium with numerous mucus-secreting cells lined the lips with no taste buds. Stratified squamous epithelia lined the oesophagus in the anterior portion which turned into a columnar epithelium towards the stomach. The lamina propria had numerous tubular glands throughout the entire oesophageal length. The stomach consisted of three distinct regions (cardiac, fundic, and pyloric) with distinguished lamina propria glands. The intestinal mucosa was thrown into villi of varying heights, with the tallest in the anterior part, lined with a simple columnar epithelium with numerous lymphocytes-like infiltrations. Numerous goblet cells appeared in the intestinal lamina epithelialis; these increased uniformly towards the anal opening. The liver was divided into lobules, with a central vein. Hepatocytes were visibly arranged closely, forming irregular cords, and the scattered tubular acinar glands formed the exocrine pancreas (hepatopancreas). Stomach content analysis indicated that the fish eats plankton, mollusks, crustaceans, and insects as the main proportion of its diet.

Histological, histochemical and ultrastructural analysis reveals functional division of the oesophagogastric segment in freshwater tubenose goby Proterorhinus semilunaris Heckel, 1837

Histological and histochemical features of the oesophagogastric segment of the alimentary canal as well as ultrastructure of gastric gland cells of freshwater tubenose goby Proterorhinus semilunaris were examined. The studies revealed that despite the lack of anatomical distinction, the oesophagogastric segment is histologically divided into the oesophagus, oesogaster and stomach, which provides evidence for the functional compartmentation of this organ. The oesophagus was characterised by the presence of numerous goblet cells secreting mainly a mixture of neutral and acid mucopolysaccharides. In the stomach, the apical zone of the surface epithelial cells contained neutral mucopolysaccharides. Numerous proliferating cells were scattered throughout the surface epithelium. In the lamina propria of the stomach, a well-developed layer of gastric glands was observed. The glands were of the alveolar type and occupied nearly the entire length of the stomach except the pyloric region. The gastric gland cells were varied into light and dark; however, their ultrastructure was identical. All cells had numerous mitochondria and a well-developed tubulovesicular system typical for the oxynticopeptic cells, but pepsinogen granules were not present in the cytoplasm of these cells. These findings contribute new evidence to literature reports that not all gobiid fish are stomachless. Moreover, they suggest higher adaptation of the species to utilise protein-rich food compared to stomachless fish, and its ability to adjust the alimentary canal quickly to changing diet. How this may facilitate establishment of P. semilunaris in invaded environments remains an open question.

Comparative Histomorphological and Histochemical Studies on the Oesophagus of Nile Tilapia Oreochromis niloticus and African Catfish Clarias gariepinus

The present work aimed to describe and compare both gross and microscopic structure of the oesophagus of Nile tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus). For this purpose, 60 specimens of oesophagus of Nile tilapia (omnivorous fish) and African catfish (carnivorous fish) were collected and processed. Anatomically, the oesophagus of both species appeared as a short tube with longitudinal mucosal folds. Using scanning electron microscope, the epithelial surface of the esophagus showed primary and secondary mucosal folds in both species while tertiary folds were observed in that of tilapia only. Histologically, the oesophagus consisted of four distinct layers: mucosa, submucosa, muscularis, and serosa. The oesophageal mucosa consisted of stratified epithelium with few mucous secreting cells in catfish and many mucous secreting cells in tilapia. Two types of mucous secreting cells reacted positively with both periodic acid shiff (PAS) and alcian blue (AB); rounded and elongated cells that were recognized in the esophageal epithelium of tilapia and only elongated oval cells were observed in that of catfish. In conclusion, the obtained histomorphological differences in esophagus of both fish species may be attributed to their different feeding habits and type of food.

Gross morphology and histology of the alimentary tract of the convict cichlid Amatitlania nigrofasciata

The primary objectives of this study were to document the macroscopic and histological structure of the alimentary tract (AT) of the convict cichlid Amatitlania nigrofasciata, because there are no data available for this omnivorous freshwater fish of the family Cichlidae. The morphology of the AT of A. nigrofasciata resembles that of related species. While having morphological criteria of the AT typical of most omnivorous fishes, such as a blind sac stomach and medium length intestine, A. nigrofasciata also has some structural peculiarities: the oesophagus is lined by a uniform stratified squamous epithelial layer with interspersed goblet cells along its entire length. Additionally, it has well-developed layers of the tunica muscularis including muscle fibre bundles that ascend into its mucosal folds. Occasionally, taste buds are present. In the transitional area between oesophagus and stomach, a prominent torus-like closure device is present. The mucosa of the stomach cannot be divided into different regions according to mucosal and morphological properties. The simple pattern of intestinal loops of A. nigrofasciata has few variations, irrespective of sex, mass and length of the individual fish. The first segment of the intestine is characterized by the largest mucososerosal ratio and the most complex mucosal surface architecture. A distinction of midgut and hindgut was not possible in A. nigrofasciata due to lack of defining structural components as described for other fish species.

Morphohistology of the digestive tract of the damsel fish Stegastes fuscus (Osteichthyes: Pomacentridae)

This study investigated the morphohistology of the digestive tract and the mean intestinal coefficient of the damsel fish Stegastes fuscus captured from the tidal pools of Northeastern Brazil. The wall of the digestive tract of S. fuscus is composed of the tunica mucosa, tunica muscularis, and tunica serosa. The esophagus is short with sphincter and thick distensible wall with longitudinally folded mucosa. Mucous glands are predominant, and the muscular layer of the esophagus presented striated fibers all along its extension. The transition region close to the stomach shows plain and striated muscular fibers. Between the stomach and intestine, there are three pyloric caeca. The intestine is long and thin with four folds around the stomach. The anterior intestine presents folds similar to those of pyloric caeca. The estimated mean intestinal coefficient and characteristics of the digestive system of S. fuscus present morphological adequacy for both herbivorous and omnivorous feeding habits.