Histological structure of the digestive tract, liver, and pancreas of Ambassis nalua (Hamilton, 1822) with ultrastructural details of the gastric gland.

The scalloped perchlet Ambassis nalua is one of the dominant fishes in the Estuarine Pranburi River, Thailand. It is suggested that this fish is a secondary trophic level with the carnivorous nature. Studies on the digestive system will help us further identify the niche of this species in the food web/food chain. The present study hence aimed to report the detailed structure and ultrastructure of A. nalua digestive system. Fish samples (n = 30) with a total length of 5.7 ± 0.5 cm were obtained by beach seines from the Estuarine Pranburi River. Their digestive tract length and intestine coeficient were 3.6 ± 0.07 cm and 0.91, respectively. Light microscopic observation showed that the digestive wall contained four layers including mucosa, submucosa, muscularis, and serosa. The prominent mucous-secreting cells were found in the mucosal esophagus. The stomach had many gastric folds, height and width of which were 649.76 ± 85.15 μm and 370.30 ± 68.56 μm, respectively. Gastric glands were found in the anterior stomach, but not in the posterior stomach. Each gastric gland was made up of a single type of columnar cells. The gastric cells were ultrastructurally characterized by numerous mitochondria and well-development of secretory granules with varying sizes. A few small vacuoles were also identified in the apical area of the gastric cells. The intestine had two regions (anterior and posterior intestines), and pyloric caecum was absent. The density of goblet cell was significantly higher in the posterior intestine. These results provide basic knowledge about the digestive system of A. nalua, and the low intestine coefficient and the absence of pyloric caecum suggest the carnivorous feeding habit of this species. This article is protected by copyright. All rights reserved.