Objective: Knowledge of diet composition and feeding habits are essential to our understanding of fish ecological adaptation and aquaculture studies. This study aims to gain knowledge on diet composition, feeding intensity and habits for Glossogobius giuris – a commercial goby residing in brackish to freshwater regions of the Vietnamese Mekong Delta.

Methods: A collection of 1,291 samples (632 males and 659 females) were caught monthly from January 2020 to December 2020 at four sites using trawl nets. A combined analysis of prey occurrence and weight was used to calculate the diet composition of this fish.

Results: This fish displayed high feeding intensity, and its diet composition was seen to be comprised of small fish, Acetes spp., Uca spp., molluscs, and others (e.g., detritus and fish scales). Although males and females of two fish size groups, two seasons and at the four sites displayed the same feeding trends as Costello graphical analysis showed, the diet composition was seen to vary with season and site. It suggested that the difference in salinity between seasons and the four sites regulated food composition within this fish.