Anatomical, histological and histomorphometric study of the intestine of the northern pike (Esox lucius)

BACKGROUND: The northern pike Esox lucius is a fresh water species belonging to the Esocidae family. It is a carnivorous fish which mostly feeds on invertebrates and fishes. The morphology of its intestine is very useful for understanding the fish’s digestive physiology, diagnosing some intestinal diseases and formulating suitable feeds. OBJECTIVES: This study was designed to determine the anatomical, histological and histomorphometric properties of the intestine of E. lucius. METHODS: The intestines of five E. lucius were examined in this study. After anatomical dissection, the histological specimens were taken and fixed in 10% formalin. Then, tissue passages were stained with hematoxylin-eosin, and Masson’s trichrome. RESULTS: The anatomical examination showed the short intestine with intestinal coefficient 0.68±0.09 in E. lucius which is a characteristic of the carnivorous species. The histological study revealed that the intestinal wall of E. lucius is composed of tunica mucosa, submucosa, muscularis, and serosa. The muscularis mucosa was not visible in the intestine. The stratum compactum is present between tunica mucosa and tunica submucosa. The histomorphometric results differentiated between three parts in the intestine of E. lucius namely anterior, middle and posterior. The maximum height of mucosal folds was observed in the anterior intestine due to its role in nutrient absorption. The mucosal fold’s height then decreased towards the posterior intestine. The tunica muscularis is significantly thicker in the anterior intestine, and the circular muscle layer is thicker than the longitudinal muscle layer throughout the entire length of the intestine. The posterior intestine possessed large numbers of goblet cells in comparison with other parts of the intestine, to promote elimination of unabsorbed particles. CONCLUSIONS: The results of this study revealed adaptation for the species feeding habits, so as to protect the intestine and increase absorptive processes.