Digestive tract microstructure characteristics and dietary analysis of Mastacembelus armatus

【Objective】This study aimed to investigate digestive tract microstructure characteristics and dietary chara-cteristics of Mastacembelus armatus， providing theoretical reference for artificial propagation and domestication， population resource conservation and restoration， and appropriate utilization of wild Mastacembelus armatus.【Method】Hematoxylin-eosin （HE） staining was used to observe the digestive tract microstructure of Mastacembelus armatus， and DNA metabarcoding technology was utilized to analyze its dietary characteristics.【Result】The digestive tract of Mastacembelus armatus composed of four layers: the mucosal layer， submucosa， muscular layer， and serosal layer. The longitudinal folds of the mucosal layer in the esophagus were well-developed with branches， and the surface was covered with stratified squamous epithelium， with goblet cells interspersed among the epithelial cells. The stomach was the most expanded organ of the digestive tract， with the mucosal layer protruding inward to form mucosal folds， consisting of the lamina propria and simple columnar epithelium， with no goblet cells observed. The intestinal villi were well-developed， and the fold height in the foregut was significantly higher than that in the midgut and hindgut （P<0.05）. A total of 409 species belonging to 24 phyla were identified from the stomach contents using 18S rDNA metabarcoding sequencing. At phylum level， the dominant groups were Arthropoda， Annelida， and Chlorophyta. At species level， the dominant species included Phyllomacromia nyanzana， Amynthas sp. GZ201102-03， and Macrobrachium superbum. The feeding selectivity analysis revealed that Mastacembelus armatus exhibited a strong preference for Annelida and Arthropoda， while showing a distinct avoidance tendency toward Chlorophyta， Bacillariophyta， and Gastrotricha， which were relatively abundant in the aquatic environment. No fundamental shift in the major dietary components was observed across different body length groups of Mastacembelus armatus， with Annelida and Arthropoda as the dominant groups at phylum level.【Conclusion】The digestive tract structure of Mastacembelus armatus exhibits typical morphological adaptations of carnivorous fish， characterized by a lubricating esophagus-expanded stomach-absorption dominated by foregut pattern. Mastacembelus armatus is a euryphagous carnivorous fish， and its feeding selection conforms to the optimal foraging theory， showing strong active selectivity for Arthropoda and Annelida at both phylum and species levels， while exhibiting avoidance toward low-trophic-level phytoplankton. With individual development， the limitations of mouth gape and energy metabolism demands drive its dietary preference to shift toward arthropod groups.