We present an alternative approach to understand and assess vulnerability of wild fish communities subjected to persistent heavy metal burdens from point-sources. The framework parameterized with some synthetic parameters have been coined as VAHMB (Vulnerability assessment for heavy metal bioaccumulation). Tissue metal concentrations (Cadmium, Lead, Mercury) in brown trout (Salmo trutta fario) and habitat metal signatures (sediment loads) was studied in six brooks inside Boletice Military Training Area (Boletice MTA), Czech Republic. Heavy metal burdens in the sediments of military area brooks were flagged safe. The tissue concentration of metals never touched critical limits but numerous cases of breaching Q3-ceilings (>75% of the critical limit) were recorded. Majority of vulnerable bioaccumulation cases were restricted to shooting area (large gears) brooks and observed for Hg. Highest bio-affinity was exhibited by Hg followed by Cd and Pb. Significantly strong, positive multicollinearity exists among heavy metals and between sediment-flesh metal concentrations. No morpho-biological dependency on heavy metal uptake was observed, however, negative implications on population fitness (Fulton’s condition factor) was apparent. A ‘nascent heavy metal exposure (NHME)’ at certain sediment metal concentrations was observed during which population fitness steeply deteriorates. It is followed by a ‘range of active adaptation (RAA)’ where deterioration of population fitness finally stabilizes. Under prevailing conditions in Boletice MTA, bioaccumulation of Cd and Pb up to critical levels seem difficult; even though Cd can bioaccumulate beyond Q3-ceilings. Prominent threat exists for reaching critical Hg bioaccumulation levels. Brooks adjacent to shooting areas should be subjected to periodic monitoring of Hg.