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

Comparative Nutritional and Histological Analysis of Malabar Red Snapper (Lutjanus malabaricus) and Asian Seabass (Lates calcarifer)

This study offers a comprehensive morpho-histological analysis of the gastrointestinal tract (GIT) of the Malabar red snapper. A comparison of its GIT morphology with that of the Asian seabass reveals similarities and differences between the two species. Additionally, the moisture content, crude protein, and ash in the fillets of Malabar red snapper and Asian seabass were slightly different, with Malabar red snapper exhibiting higher levels of essential fatty acids. Furthermore, higher levels of the polyunsaturated fatty acid (PUFA)/saturated fatty acid (SFA) ratio and docosahexaenoic acid (DHA)/eicosapentaenoic acid (EPA) ratio, and a lower omega-6/omega-3 ratio, were observed in Malabar red snapper compared to Asian seabass. The Malabar red snapper's esophagus featured protective mechanisms such as simple columnar epithelial cells, mucous-secreting glands, and goblet cells that were predominantly stained for acid and neutral mucosubstances. Furthermore, its stomach, with mucus cells that were weakly stained for acid mucosubstances, exhibited distinct regions with varying glandular densities, with the pyloric region featuring few glands. The pyloric caeca of the fish were composed of five finger-like structures and few goblet cells. Several goblet cells gradually increased from the anterior to the posterior region of the intestine. These findings provide useful insights for the aquaculture sector, focusing on Malabar red snapper.

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.

Morphological and Molecular Functional Evidence of the Pharyngeal Sac in the Digestive Tract of Silver Pomfret, Pampus argenteus

The pharyngeal sac is a comparatively rare organ in the digestive tract among teleost fishes. However, our understanding of this remarkable organ in the silver pomfret (Pampus argenteus) is limited. In the present study, we examined the various morphological and histological characteristics of the pharyngeal sac using histochemical techniques and electron microscopy. The pharyngeal sac showed unique characteristics such as well-developed muscular walls, weakly keratinized epithelium, numerous goblet cells, and needle-like processes on the papillae. The porous cavity of the papillae contained numerous adipocytes and was tightly enveloped by type I collagen fibers. These structures might provide mechanical protection and excellent biomechanical properties for grinding and shredding prey. A comparison of gene expression levels between the pharyngeal sac and esophagus using RNA-seq showed that phenotype-associated genes (epithelial genes and muscle genes) were upregulated, whereas genes related to nutrient digestion and absorption were downregulated in the pharyngeal sac. These results support the role of the pharyngeal sac in shredding and predigesting food. Overall, these findings provide a clearer understanding of the pharyngeal sac morphology and explain the morphological adaptations of the digestive tract for feeding on gelatinous prey. To our knowledge, this is the first report on pharyngeal sac gene expression in P. argenteus.

The delimitation of intestine segments of koi carp (Cyprinus carpio var. koi) based on histological features

In this study, the delimitation of intestine segments of koi carp (Cyprinus carpio var. koi) was conducted using a histological approach with the measurements of height of mucosa folds (HF), width of mucosa folds (WF), thickness of muscularis (TM) and cross-sectional area (CSA). According to the change trends for these four parameters, the intestine of the koi carp was divided into anterior intestine, middle intestine and posterior intestine. The locations of the three intestine segments were defined, and their ratios along the entire intestine were accounted for 23.84 ± 1.18%, 46.77 ± 2.29% and 29.39 ± 1.65%, respectively. The anterior intestine had a significantly higher HF, compared with the middle (p < .01) or posterior intestines (p < .01). The muscularis became thin gradually from the anterior intestine to posterior part. TM was significantly different among the anterior, middle and posterior intestines (p < .01). The anterior intestine had a significantly higher CSA, compared with the middle (p < .01) and posterior intestines (p < .01), and the latter two segments had similar CSA values (p > .05). The procedure of the delimitation of the koi carp intestine segments can offer useful information for future studies on other fish species. The presented results are meaningful for studies on differential functions of the different intestine segments in fish.

An ultrastructural focus on the buccal cavity of the grey gurnard Eutrigla gurnardus (Linnaeus, 1758): Adaptative dietary implications

The current investigation represented the first anatomical description of the buccal cavity of the grey gurnard Eutrigla gurnardus. For the achievement of this study, 10 heads of mature fish were used for SEM examinations. The morphological characteristic appearance of the buccal cavity has shown several adaptations in relation concerning its feeding habits. The median fissure of the upper lip divided the upper lip into two halves, this fissure appeared to be formed from many micro-tubercles with numerous taste buds which aid in holding mucus secretion to the cell surface, help in mucus spread, and provide mechanical protection to the epithelium. Velum had two regions: median and peripheral region. The epithelium covering of the median region of the upper velum had dots-like epithelial protrusion that carrying numerous taste buds, meanwhile, the epithelium covering of the lower velum not carried taste buds but instead carried numerous small scales-like structures. The palate is divided into two semicircular regions by small region of microridges into the anterior and posterior region. The slightly bifid tongue had a median tubercle with numerous small taste buds on its dorsal surface. Concluded, these data were necessary to understand the adaptation of fish to its habitat and in developing a new and better method for fishing of this type of fish.

Activin A affects feeding by promoting the inner diameter and muscle development of the pharynx and oesophagus in zebrafish (Danio rerio) larvae

Activin A belongs to the superfamily of transforming growth factor-β and plays an important role in hormone regulation and tissue development. However, few research studies have been conducted on the effect of activin A on feeding organs in fish. In this study, the zebrafish (Danio rerio) larvae were treated with 1 ng ml^-1 activin A for 8 days continuously. The haematoxylin and eosin (H&E) staining section results revealed that the transverse inner diameter of the pharynx and oesophagus significantly increased on the third and eighth days after treatment compared with the control group (P < 0.05). On the eighth day, the cross-sectional area of the pharyngeal muscle increased by 8638 μm² compared to the control group (P < 0.05). The RNA in situ hybridization results also showed that the expression of skeletal muscle-specific genes (myog and myod) was significantly increased in pharyngeal muscle on the eighth day. Furthermore, the qRT-PCR results showed the expression of gh gene was significantly increased on the eighth day (P < 0.05). At the same time, more larvae in activin A group were able to feed larger brine shrimp (Artemia) than in the control group on the eighth day. In conclusion, activin A could affect feeding by promoting the inner diameter and muscle development of the pharynx and oesophagus in zebrafish larvae. This study is the first to report that the development of the pharynx and oesophagus can directly affect food intake in fish larvae, which provides a theoretical basis for the study of food intake of fish at an early stage.

Morpho-histochemical adaptations of the digestive tract in Gangetic mud-eel Ophichthys cuchia (Hamilton 1822) support utilization of mud-dwelling prey

Freshwater mud-eel, Ophichthys cuchia is nocturnal, carnivorous and economically important fish, yet its digestive physiology is unknown. We therefore studied the gastrointestinal (GI) tract of O. cuchia using morphological, osteological, histological and histochemical approach to understand how the structural adequacy of GI tract helps in acquisition of bottom and mud-dwelling prey and supports utilization of uncommon food resources. Morphologically the GI tract showed typical features of carnivorous fishes in the form of sub-terminal mouth, short muscular esophagus, expendable stomach, short intestine and rectum. Osteological investigation clearly showed that the specialized arrangement of teeth in the oral cavity and pharyngeal region helps in digging and manipulation of bottom and mud-dwelling prey. Longitudinal mucosal folds, stratified squamous epithelium with numerous goblet cells of esophagus protect mucosa from mechanical harm and also allow easy transit of prey into the stomach. Large-sized rugae of stomach are complemented with numerous gastric glands which together increase the transit time of carnivorous food stuff and ensure its complete digestion. The pylorus specifically allows only digested and finely ground food stuff into the intestine and thus avoids the intestinal blockage due to entry of undigested food. The enterocytes and goblet cells of intestine are absorptive and lubricative in their functions respectively. A significant increase in the number of goblet cells and thickness of muscularis from the intestine to the rectum was evident which facilitates the easier transit of food, protection for the epithelium from abrasion, and helps in defecation. Histochemistry revealed that the mucins are secreted throughout the GI tract and thus catalyze faster digestion of carnivorous food stuff, providing protection to mucosal membrane from abrasion, acts as a co-factor to support digestion, absorption of proteins, ions, fluids and helps in defecation. The outcome of this study clearly supports the notion that structural adaptations in the digestive tract of fishes can be effectively used as a blueprint to understand why and how particular fish species feed and use unique food. Additionally, the structural and functional adequacy of the digestive tract helps the fishes to acquire and utilize novel habitats and food resources. The results presented in this study will serve as a reference point for future studies, which focus primarily on understanding the evolution of carnivory in Synbranchids.

Diet and histological features of digestive tube from four discarded fish species by trawl bycatch in Northeastern Brazil

Abstract: Fish feeding habit associated to the morphology of their digestive tube can provide useful biological and ecological information. Between January and December 2012, we examined 16 fish species discarded by trawl in the Potiguar basin, northeastern Brazil, and classified them into four groups according to Alimentary Index - IAi. Our aims were to: (1) provide information on diet composition of one species represented by each group (Opisthonema oglinum, Conodon nobilis, Larimus breviceps and Sphoeroides testudineus), (2) examine the morphology of their digestive tube, and (3) associate ingested food items with the morphological features. Stomach contents were collected and classified according to IAi: main, accessory and secondary categories; fragments of esophagus, stomach, and small intestine were examined using paraffin section technique. Biometric data (total length-TL, standard length-SL and total weight-TW), stomach weight-SW, and gonadal weight-GW were recorded and applied in two indices: (1) the stomach Repletion Index - SRI (SRI = SW/TW × 100) and (2) the gonadosomatic index - GSI (GSI = GW/TW × 100) for the analyses of feeding and reproductive activities, respectively. The main food categories were (1) Teleostei for C. nobilis, (2) Crustacea for L. breviceps and O. oglinum, and (3) Mollusca for S. testudineus. The feeding activity was higher during the dry season, while the GSI was higher in the rainy season. The morphological analysis revealed a regular structure of the tissues analyzed. We highlight the presence of tubular gastric glands and strong muscular walls in the stomach (O. oglinum; L. breviceps); well-developed pyloric caecum in the intestine (O. oglinum; C. nobilis; L. breviceps); and presence of pseudo-stomach (S. testudineus). Our study confirms that the digestive tube of the examined species has morphological adequacy for carnivorous feeding habit, providing useful information on tissue structures associated to diet composition.

The digestive tube of Piaractus brachypomus: gross morphology, histology/histochemistry of the mucosal layer and the effects of parasitism by Neoechinorhynchus sp

The objective of the present study was to describe the histology and histochemistry of the mucosal layer of the digestive tube of Piaractus brachypomus, and the histopathology associated with parasitism by Neoechinorhynchus sp. The digestive tube of P. brachypomus consists of three macroscopically distinct portions: short, rectilinear and elastic-walled ooesophagus, J-shaped siphon stomach and a long intestine with rectilinear and curved portions, defined by patterns of villi as foregut, midgut, and hindgut. Histological and histochemical differences were observed in the mucosal layers of the different digestive tube regions, such as intense production of neutral and acidic mucous substances in the pseudostratified mucosal epithelium of the oesophagus; positive periodic acid Schiff reagent (PAS)reactions at the apex of the columnar epithelial cells of the stomach and increased intensity of histochemical reactions in the hindgut region. Neoechinorhynchus sp. was present in 85.7% of specimens examined, with a mean intensity of 7.4 ± 6.2 (±) and abundance of 6.33. Good health of the fish indicated by high relative condition factor values ( _Kn ) and occurrence of only mild to moderate alteration in the mucosal layer indicated that Neoechinorhynchus sp. exhibits low pathogenicity towards P. brachypomus hosts in farming environments, with low levels of infection.

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.

Study on the morphology, histology and enzymatic activity of the digestive tract of Gymnocypris eckloni Herzenstein

The present research was conducted to study the morphology, histology and enzymatic activities of the digestive tract of Gymnocypris eckloni by light and transmission electron microscopes as well as by enzyme assays. The digestive tract of G. eckloni consisted of the oropharyngeal cavity, oesophagus and intestine. The wall of the digestive tract was composed of mucosa, submucosa, muscularis and serosa but lacked muscularis mucosa and glands. The stratified epithelium of the oropharyngeal cavity and oesophagus contained numerous mucous cells. Taste buds were found in the epithelium of the oropharyngeal cavity. A large number of isolated longitudinal striated muscular bundles were present in the submucosa of the oesophagus. The mucosal epithelium of the intestine was composed of simple columnar cells containing absorptive, goblet and endocrine cells. Numerous mitochondria and endoplasmic reticulum were observed in the absorptive cells, especially in the anterior intestine. From the anterior to the posterior intestine, the number and length of mucosal folds and microvilli decreased, but the number of goblet cells increased. The intestinal coefficient was 2.38. Maximum trypsin activity was measured in the anterior intestine, while the lowest lipase and amylase activities were tested in the middle and posterior intestines, respectively. The results provided experimental evidence for evaluating physiological condition of G. eckloni digestive tract, which will be useful for improving current rearing practices and diagnoses of digestive tract diseases.

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.

Morpho-histological characterisation of the alimentary canal of an important food fish, Asian seabass (Lates calcarifer)

Asian seabass (Lates calcarifer) is a food fish of increasing aquaculture importance. In order to improve our understanding on the digestive system and feeding of this species, morphological and histological features of the gut were studied. Morphologically, the Asian seabass gut is defined by a short and muscular esophagus, well-developed stomach and comparatively short intestine. Mucous secreting goblet cells reactive to PAS (Periodic Acid Schiff) and AB (Alcian Blue) stain were present throughout the esophagus. The stomach was sac-like and could be distinguished into the cardiac, fundic and pyloric regions. Gastric glands and mucus cells were predominately present in the cardiac and fundic regions. Five finger-like pyloric caeca were present between the stomach and intestine. The intestine was a short, tubular structure with no morphological differences between the various regions. Histologically, the intestinal regions were similar, the main difference being in the number of goblet cells that increased from anterior to posterior intestine, with 114 ± 9, 153 ± 7 and 317 ± 21 goblet cells in the anterior, mid and posterior regions, respectively. The intestinal epithelium stained positively for PAS, but the staining was stronger for acidic glycoproteins. The rectum was similar to intestine, except for increased goblet cell numbers (anterior rectum: 529 ± 26; posterior rectum: 745 ± 29). Gut morpho-histology did not respond to salinity changes, however, there was a significant reduction of mucosal height, goblet cell numbers and muscularis thickness upon food deprivation.

Ultrastructure of the digestive tract in neotropical carnivorous catfish Hemisorubim platyrhynchos (Valenciennes, 1840) (Siluriformes, Pimelodidae)

The surface of the digestive tract of Hemisorubim platyrhynchos was analyzed by scanning electron microscopy. Morphometric studies by transmission electron microscopy were performed to analysis the intestinal microvilli. H. platyrhynchos is a Neotropical carnivorous freshwater catfish featuring a short digestive tract composed of a short esophagus, saccular stomach, and intestine with four regions: anterior, middle, posterior, and rectal. The esophageal surface is constituted by fingerprint-like microridges that anchor the mucosubstances secreted by goblet cells facilitating the passage of food. Goblet cells present the opening to the esophageal lumen, between the microridges. Club cells are in basal epithelium and they do not present the opening to the lumen. The gastric luminal surface shows polygon-shaped epithelial cells which secrete granules by exocytose to protect the gastric surface. The intestinal luminal surface reveals folds that are thicker in the anterior intestine than in the posterior intestine, increasing the absorptive surface area. The intestinal surface presents the microvilli of enterocytes and the opening of goblet cells. The morphometric analysis showed that the microvilli are longer in the anterior intestine, significantly decreasing towards the posterior intestine. The microvilli surface area significantly is greater in the anterior and middle intestine than in the posterior intestine. Numerous openings of goblet cells were observed in the posterior intestine acting in epithelial protection and lubrication. SCANNING 38:336-343, 2016. © 2015 Wiley Periodicals, Inc.

Histological features of the gastrointestinal tract of wild Indonesian shortfin eel, Anguilla bicolor bicolor (McClelland, 1844), captured in Peninsular Malaysia

This study was conducted to record the histological features of the gastrointestinal tract of wild Indonesian shortfin eel, Anguilla bicolor bicolor (McClelland, 1844), captured in Peninsular Malaysia. The gastrointestinal tract was segmented into the oesophagus, stomach, and intestine. Then, the oesophagus was divided into five (first to fifth), the stomach into two (cardiac and pyloric), and the intestine into four segments (anterior, intermediate, posterior, and rectum) for histological examinations. The stomach had significantly taller villi and thicker inner circular muscles compared to the intestine and oesophagus. The lamina propria was thickest in stomach, significantly when compared with oesophagus, but not with the intestine. However, the intestine showed significantly thicker outer longitudinal muscle while gastric glands were observed only in the stomach. The histological features were closely associated with the functions of the different segments of the gastrointestinal tract. In conclusion, the histological features of the gastrointestinal tract of A. b. bicolor are consistent with the feeding habit of a carnivorous fish.

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.

Morphological study of the asymmetrical buccal cavity of the flatfish common solea (Solea solea) and its relation to the type of feeding

OBJECTIVE

To investigate the surface architecture of the asymmetrical buccal cavity of Solea solea which are considered one of the most important predators in benthic communities.

METHODS

Adult Solea solea were obtained from Mediterranean Sea near Damietta. The heads were removed and processed for scanning electron microscopy. Its buccal cavity is asymmetrical and divided into roof and floor and the tongue for histological studies.

RESULTS

The buccal cavity roof is formed from upper jaw, velum and the palate. The upper jaw has several wing like processes with teeth arranged in several rows which may help in cutting and pushing the food to the entrance of the digestive canal while the floor is formed from the lower jaw and the tongue. The tongue is divided into apex, body and root. There is a gradual decrease of goblet cells in the tongue from anterior to posterior. These goblet cells function in protection of the epithelium.

CONCLUSIONS

Teeth in the floor of the buccal cavity and taste buds can be considered adaptive changes of the oral cavity related to the feeding habits and was a source to identify new and better methods of nutrition in aquaculture of Solea solea.

Histological assessments of intestinal immuno-morphology of tiger grouper juvenile, Epinephelus fuscoguttatus

Histological assessments on the intestinal morphology and immunity of tiger grouper juveniles, Epinephelus fuscoguttatus help in determining the earliest age to start an oral vaccination. This study describes the morphological development of the intestinal immunity of tiger grouper of various ages. Clinically healthy tiger groupers were selected and divided into 4 groups of 20 fish per group. Groups 1, 2, 3 and 4 consisted of juveniles of 30, 60, 90 and 120 days old, respectively. The whole intestine was collected and divided into three regions, the anterior, mid and posterior intestine and fixed in 10% buffered formalin before slides were prepared for microscopic examinations. It was found that the histological structures of the anterior intestine were for absorption of nutrient from digested food particles. The significantly (p < 0.05) higher number and length of the intestinal villi and smaller gap between villi were observed in the anterior intestine, which were structures for absorption. Structures of the posterior intestine were for immunity especially the adaptive immunity with included significantly (p < 0.05) higher numbers of the lymphoid and goblet cells, and significantly (p < 0.05) thicker lamina propria, which were structures for immunity. The mid intestine was the transition structure that involved in both absorption and innate immunity. The results also revealed that leukocytes existed in the lamina propria of 30-days old tiger groupers, an indication that the immune system was present at that particular age.