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Histological features of the digestive tract of the adult European hake Merluccius merluccius (Pisces: Merlucciidae)

Abstract The digestive tract of five adult specimens of the European hake, Merluccius merluccius L., from Eastern Adriatic, were analysed histologically in 2011, using haematoxylin–eosin and Alcian blue/PAS (Periodic Acid Schiff) methods. The paraffin sections of oesophagus, stomach, intestines, liver, gall bladder and pancreas have been stained with a hematoxylin–eosin technique in order to elucidate the main histological features of the digestive tract. The wall of oesophagus and stomach is formed by four distinctive layers, while those of the intestines and gall bladder consist of three layers: the mucosa, the muscular and the outer layer. The mucosa is the innermost layer, which usually consisted of three different layers: epithelium, lamina propria and muscularis mucosae. The submucosa is a layer of connective tissue and it was not seen in the intestines and gall blader. In the oesophagus, stomach and intestines, as well as in the gall bladder, the muscular layer consists of two layers of muscle fibres: circular and longitudinal. The outermost layer of the upper parts of the visceral organs is adventitia consisting of connective tissue. In the caudal parts of digestive tract, this layer is replaced by serosa. The liver consists of hepatocytes containing a mass of lipid droplets. The pancreatic tissues contain serous acini. The present study suggests that histological features of the digestive tract of the hake Merluccius merluccius L. are mostly similar to those of other carnivorous fish, and according to its feeding habits.