Research Article |
Corresponding author: Mohd Y. Bhat ( myousufpp@yahoo.com ) Corresponding author: Irfan A. Rather ( rather@ynu.ac.kr ) Academic editor: Carolina Arruda Freire
© 2019 Mohd Y. Bhat, Ashok Channa, Bilal A. Paray, Mohammed K. Al-Sadoon, Irfan A. Rather.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Bhat MY, Channa A, Paray BA, Al-Sadoon MK, Rather IA (2019) Morphological study of the gastrointestinal tract of the snow trout, Schizothorax esocinus (Actinopterygii: Cypriniformes). Zoologia 36: 1-7. https://doi.org/10.3897/zoologia.36.e31791
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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.
Buccopharynx, esophagus, intestinal tract
Ultrastructural studies are important to understand the relationship between physiological and biochemical functions and molecular mechanisms of an animal (
The snow trout, Schizothorax esocinus Heckel, 1838 (Cypriniformes: Cyprinidae), is a native freshwater teleost fish that inhabit cold streams, rivers, and lakes (
All procedures were carried out according to the ethical principles of animal experimentation adopted by the Ethics Committee on Animal Use of the University of Kashmir, India. Live specimens of snow trout, S. esocinus, weighing 300 to 350 g (total length ranging from 25 to 32 cm) were collected from different freshwater sources of Kashmir valley. After being anesthetized with tricaine methanesulfonate, MS 222, solution by using a dosage of 100 mg L−1, the fishes were euthanized via a longitudinal incision through their ventral side. After dissection, various segmental tissue fragments of the alimentary tract viz. buccopharynx, esophagus, intestinal bulb, intestine and rectum of 2 cm long were removed and immediately processed for scanning electron microscopic studies. The esophagus, intestinal bulb, intestine, and rectum were incised and split longitudinally to expose the mucosal surface and rinsed in normal saline to remove excess mucus and other adhered particles. The tissues were then fixed in 2.5% glutaraldehyde buffered with 0.1 M sodium cacodylate at pH 7.3 for 18–48 hours. Following this primary fixation, the samples were then thoroughly rinsed three times in 1 M cacodylate buffer and post-fixed for two hours at room temperature in 1% osmium tetraoxide buffered at pH 7.3 with 0.1 M cacodylate (secondary fixation). The post-fixed tissues were washed three times in buffer, dehydrated in ascending grades of ethanol and transferred to a 100% amyl acetate bath. The tissues were then critical-point dried through liquid CO2 in Hitachi HCP-2 dryer and mounted on aluminum stubs with silver paint. These were sputter-coated with gold in a Hitachi HUS-5GB high vacuum evaporator. The coated specimens were examined in a Hitachi S-3000H scanning electron microscope.
Scanning electron microscope observations of the mucosal surface of the buccopharynx, esophagus, intestinal bulb and intestine of snow trout, S. esocinus reveal prominent longitudinal mucosal folds or major mucosal folds which left deep furrows in between (Fig.
The primary longitudinal and secondary mucosal folds in the epithelium of the esophagus are visible along with goblet cells (Figs
The SEM observation on the anterior intestine shows the organization of longitudinal mucosal folds (Fig.
Scanning electron micrograph of intestinal bulb showing: (6) primary or major (MF1) and secondary mucosal folds (MF2), covered with thin film of Mucin (M). The zig-zag arrangement of primary folds is clearly visible in this region (←); (7) microridges (MR); (8) primary or major mucosal folds (MF1) and the zig-zag invagination (←); (9) secondary folds (MF2). Scale bar: 6 = 500 µm, 7 = 10 µm, 8 = 100 µm, 9 = 20 µm.
The morpho-anatomical features of the digestive tract of Indian freshwater teleosts, in relation to their feeding habits, are well documented (
Fine anatomical features of the mucosal surface of the intestinal tract in S. esocinus as revealed by present SEM study correlated with the other teleosts (
The rectum reveals irregular mucosal foldings that increase the surface area of the rectal mucosa. The rectum plays a very little role in food storage, digestion and absorption as evidenced by the low mucosal folds as well as the absence of well-defined cavities and the minor mucosal folds, thereby bearing a close relationship with its functional aspects. A thin film of mucous secretion has been observed in the rectal mucosa, which aids in easy defecation. The occurrence of few mucous cells in between the epithelial cells of the various regions of the digestive tract of various teleosts has been reported by different authors (
On the basis of our results, the surface architecture of the mucosa of the digestive tract of S. esocinus throws light on the modifications of the mucosal epithelium and morphological characteristics of the various cells lining the alimentary canal which are useful in correlating the morphological features with function. These findings provide insights into the structure and functioning of the digestive system in this fish. Further detailed studies should be conducted on the ultrastructure level of the gastrointestinal tract of S. esocinus.
The authors would like to express their sincere appreciation to the Deanship of Scientific Research at the King Saud University, Riyadh, Saudi Arabia for funding this Research Group project no RG-1437-005.