2.1 Study area: The research was conducted at upper Meghna River and its associated tributaries of the coastal area of Chandpur district conjoint with Padma River (S1), Chittagong division, flowed downward to Mehendiganj Upazila of Barisal district Bangladesh. It is one of the most important rivers in Bangladesh which lies between the latitude 22° 38′ 35′′ N and longitude 90° 48′5 7′′ E in Bangladesh part by adjoining the Surma and Kushiyara Rivers originating from the hilly regions of eastern India as Barak River through different cities and municipalities. 2.2 Sample collection: A total of 72 fish specimens belonging to 9 species, namely Climbing perch (A. testudineus), Spotted snakehead (C. punctatus), Sisorid catfish (G. youssoufi), Stinging catfish (H. fossilis), Zig-zag eel (M. armatus), Tengara (M. tengara), Pabdah catfish (O. pabda), Ticto barb (P. ticto) and Asian fresh-water needlefish (X. cancila) were collected from 10 stations (S1 to S10) at the upper Meghna River and its associated tributaries during November 3–4, 2018. The stations S6, S7, S8 and S9 were located at the branch of Meghna River. A small mechanized boat was taken, and a cast net was thrown to collect fish species. Immediately after harvesting, fish specimens were washed thoroughly with freshwater to remove the muds or other fouling substances and put in the clean polythene bag and preserved in ice boxes at around − 1 °C. After that, specimens were brought for laboratory analysis and preserved at − 20 °C. Specimens were allowed to reach room temperature, and non-edible parts (fins, guts, scales, etc.) were removed by steam cleaned stainless steel knife. The edible portion of fish samples (muscle) was thoroughly rinsed with deionized water and chopped into thin chunks (1.5–3.0 cm) by a sharp knife on a sterilized polythene sheet. Then, the prepared samples were air-dried to remove the extra water.2.3 Sample preparation and analysis0.25 mg of muscle specimens were taken from each specimen and weighted using an electric balance. A digestion reagent was made by adding 5 mL of distilled water, 5 mL of nitric acid (HNO3, 65%) and 2 mL of hydrogen peroxide (H2O2, 30%). Then, the digestion reagent and balanced muscle specimens were kept in a Teflon vessel. Microwave (1000 W, Berghof-MWS2, Bergh of speed-wave, Eningen, Germany) was used to digest the specimens thoroughly overnight. After complete digestion, 0.42 μm pore-sized Whatman membrane filter paper was used to filter the solution pulp and kept in 50 mL poly-propylene centrifuge tubes (Nalgene, New York). Inductively coupled plasma mass spectrometer (ICP-MS, Agilent 7700 series) was conducted to analyze the selected trace metals. The calibration curve was prepared by using Multi-element Standard XSTC-13 (Spex Certi Prep, Metuchen, USA) solutions. A desired calibration precision (sdv < 20%) was used with certified reference materials to assure the analytical assessment.