THE HISTOLOGY OF THE GASTROINTESTINAL TRACT OF POMADASYS JUBELINI

Histology of the Gastro-intestinal tract of Pomadasys jubelini

The alimentary canal, from oesophagus to the rectum, consist of the following layers

1. Serosa: the outermost layer of which connective tissue are superimposed.

2. Outer longitudinal muscle layer, a thin sheet of muscular bundle having longitudinal fibre.

3. Inner circular muscle layer: a thick layer of striated and smooth muscle fibre

4. Submucosa: This layer is made up of connective tissue embedded with blood vessels, ducts and fibers

5. Muscularis mucosa: A thin layer of fibre separating the submucosa from the mucosa

6. Mucosa: A membrane of variable thickness usually from folds of different lengths depending on the region to which it belongs

The oesophagus

The outer longitudinal layer is represented by irregular bundles of fibre which permits distention while the inner circular muscle layer is of enormous thickness. These layers of tunica muscularis (longitudinal and circular muscle layers) account for the thickness of the oesophageal wall. The submucosa consists of compact connective tissue, blood vessels, fibres and gland ducts; this merges with the muscularis mucosa to extend as part of the large mucosal fold. Lots of goblet cells and oesophageal pits containing blood vessels are present.

The presence of numerous oesophageal folds and muscle layers (longitudinal and circular) observed in P. jubelini allows for the expansion of the oesophagus hence the swallowing of large substances is made possible. The goblet cells /mucus secretory pits observed along the entire length of the gut secrete mucus and perform different functions in different regions of the gut. It takes the place of the salivary gland in the buccal cavity and oesophagus. The mucus aids digestive activities in the first part of the intestine and lubricates faecal material in the rectum as well as give protection to the intestinal epithelium against mechanical damage. The presence of numerous goblet cells is typical of carnivorous species.

Transverse Section of the Oesophagus of Pomadasys jubelini

s – serosa, lm= longitudinal muscle layer, cm – circular muscle layer,

sm – submucosa, m – mucosa, g= goblet cell, (Haemotoxylin and Eosin ×40)

Stomach

This is made up of four layers, the outer longitudinal muscle, inner circular muscle, the submucosa and mucosa. The circular muscle appears to be connected by lose connective tissues; it is wider and thicker than the longitudinal muscle layer. The submucosa is made up of loose connective tissue within which blood vessels occur. The mucosa is different from other parts of the GIT. It is thick due to presence of gastric glands which are round shaped. The mucosa is thrown into large longitudinal folds with many pits. The epithelium of the mucosa is made up of undifferentiated glandular and columnar cells. Goblet cells with uniform secretory cells and gastric ducts are also present.

The large mucosal folds in the stomachs of P. jubelini are associated carnivorous species. These large folds allow fishes to accommodate a large quantity of food items as a result of its ability to distend. The undifferentiated columnar epithelia cells and mucosal folds also provide large surface area for storage in the stomach.

Transverse Section of the Oesophagus of Pomadasys jubelini

s – serosa, lm= longitudinal muscle layer, cm – circular muscle layer,

sm – submucosa, m – mucosa, g= goblet cell,

(Haemotoxylin and Eosin ×40)

Pyloric caeca

The caeca have a thin layer of longitudinal muscle, a thick circular muscle layer, muscularis mucosa, the submucosa and mucosa which is filled with connective tissue. The epithelial lining is made up of columnar absorptive cells with goblet cells for mucus secretion. The mucosa is elaborated into numerous filiform folds with a basal columnar membrane which is closely packed and clearly visible

The large mucosal folds in the stomachs are associated with carnivorous species. These large folds allow fishes to accommodate a large quantity of food items as a result of its ability to distend. The undifferentiated columnar epithelia cells and mucosal folds also provide large surface area for storage in the stomach.

Transverse Section of a Pyloric caecum of Pomadasys jubelini

cm – circular muscle, m – mucosa, V – Villi, p – pits,

(Haemotoxylin and Eosin ×40)

Intestine

The intestine is lined by a simple columnar epithelium consisting of absorptive cells and mucus-secreting cells; the serosa is thin, the inner circular muscle layer is wider than a less well developed longitudinal layer which is loosely packed by connective tissue. The muscularis mucosa is not conspicuous. The mucosa is thrown into numerous elongated folds unlike those of the oesophagus and stomach which are made up of short, thick and few folds. The folds resemble villi.

Transverse Section of the Intestine of Pomadasys jubelini

lm – longitudinal muscle, cm – Circular muscle, m – mucosa,

(Haemotoxylin and Eosin, ×40).

Rectum

The muscle layer of the rectum is much thicker than that of the oesophagus, stomach, pyloric caeca and intestine. The mucosa is considerably folded, they appear shorter and wider. Goblet cells are also present in this region though fewer than in the intestine.

This region also revealed sparse, stunted and spaced folds with the presence of villi. This situation reveals that digestion and probably absorption takes place within the whole length of the gut (Clarke and Witcomb, 1979; Banan Khojasteh et al., 2009). The dense region of blood vessels and connective tissues in the sub mucosa is prominent and varies in thickness from one region of the gut to another.

10)

Transverse Section of the Rectum of Pomadasys jubelini

lm, longitudinal muscle: cm, circular muscle: sm, submucosa;

mf, mucosal fold; es, epithelial sheath;

(Haemotoxylin and Eosin, ×40).

11)

CONCLUSION

The length of the gut of a fish speies is related to its feeding habit and just like P. jubelini, the length of its gut is ralated to the feeding habit of the fish.. The intestine is short and not coiled and allows for faster digestion of carnivorous substances.

The striated muscularis in the oesophagus with smooth muscle in the stomach, pyloric caeca, intestine and rectum consist of inner circular muscle layer and an outer longitudinal layer. The circular muscle is more prominent.

The muscular layers of the gastro-intestinal tract of P. jubelini vary in thickness from one region to another. The outer longitudinal muscle and inner longitudinal muscle layer make up the muscular layers (tunica muscularis). The prominence of these muscle layers indicates the thickness of the gut of carnivorous fishes. Banan Khojasteh et al. (2009) stated that the muscles of the gut are striated and thick and the circular muscle is more prominent than the longitudinal muscle.

REFERENCES

Bana-Khojasteh, S.M. (2012). The morphology of the post gastric alimentary canal in teleost fishes: a brief review. International journal of Aquatic sciences, 3 (2) 71-88.

Clarke , A. J. and Witcomb, D. M. (1979). A study of the histology and morphology of the digestive tract of common eel (Anguilla anguilla) Journal of Fish Biology, 16: 159-170.

Lagler, K.F., Bardarch, J.E., Miller, R.K. and MayPassino, D. R. (1978). Ichthyiology. 2^nd edition. John Wiley and sins Inc. Florida, USA. Pp129 -163.

Osman, A.H.K. and Caceci, T. (1991). Histology of the stomach of Tilapia nilotica (Linnaeus 1758) from the River Nile. Journal of Fish Biology, 38: 212-223.

Pandey, K and Shukla, J.P. (2005). Fish and Fisheries. A text book for university students. Rastogic Publications. 500pp.

Srivastava, C. B. L. (1988). A Text Book of Fisheries Science and Indian Fisheries. Kitab Mahal, Allahabad, India.

Ugwumba, A.A. and Ugwumba, O.A. (2007). Food and Feeding Ecology of Fishes in Nigeria. JodetanVentures. Ibadan. (70pp).

Posted by:
Marian Onwude Agbugui
on April 03, 2017

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