engleski

Histology of the digestive tract in the European hake (Merluccius merluccius)

The European hake (Merluccius merluccius) is a predatory demersal fish widely distributed in the Mediterranean. The adult European hake feeds mainly on fish and less frequently on crustaceans and mollusks. The aim of this study was to investigate and describe the histology of the digestive tract in the European hake. For this purpose, tissue samples of the esophagus, stomach, intestine and rectum were taken from five European hakes. The tissue samples were fixed in 10% neutral buffered formalin, embedded in paraffin and sectioned with microtome into 6 µm sections. The sections were stained using five different methods: hematoxylin and eosin, Mallory trichrome, Verhöeff-Van Gieson, Alcian blue-PAS kit and the seven-reagent kit for determining reticulin fibers. The histology of the investigated parts was analyzed by an Olympus BX41 microscope. The wall of the digestive tract was composed of mucosa, submucosa, muscularis and adventitia or serosa. According to the anatomy, thickness of the wall, length of mucosal folds and thickness of muscularis, intestine was subdivided into three parts: anterior, middle and posterior. The mucosa of the esophagus was lined by stratified squamous epithelium. The stomach and intestine were lined by simple columnar epithelium. The rectum was lined with epithelium that resembles pseudostratified columnar. Microvilli were present on apical surface of the epithelial cells in all parts of the digestive tract except in the esophagus. Mucous cells were present in all investigated parts except in the stomach. The lamina propria was composed of loose connective tissue, except in the esophagus, where it contained dense connective tissue. Abundant gastric glands were present in the cardiac part of the stomach. The muscular layer of the mucosa was identified only in the stomach. The submucosa was composed of dense connective tissue, except in the esophagus, where it contained loose connective tissue. The muscularis was composed of inner circular and outer longitudinal layers of smooth muscle cells, except in the esophagus, where it was made of striated muscle fibers. Adventitia was found to be the outermost layer of the esophagus, while serosa was present in all other parts. Melanocytes were found in different layers of the esophagus, stomach and in the serosa of the rectum. In further histochemical research the focus will be placed on defining enzyme activities along the digestive tract in the European hake.

European hake ; digestive tract ; histology

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