Non-lethal muscle biopsy sampling for mercury biomonitoring in brook trout

Repeated monitoring of individual fish is increasingly important for understanding how environmental stressors influence contaminant exposure and physiological condition in wild populations. However, assessing mercury (Hg) concentrations in relatively small-bodied fishes often requires lethal sampling, limiting the ability to repeatedly sample individuals and increasing impacts on sensitive populations. We evaluated the utility of a minimally invasive, non-lethal muscle biopsy approach for monitoring total Hg concentrations in brook trout, Salvelinus fontinalis. In a 57-day laboratory study, we examined the effects of two biopsy sizes (4 and 8 mm in diameter) on survival, growth, and body condition of brook trout (n = 60; 160-200 mm fork length), and assessed whether Hg concentrations from biopsies predicted concentrations from whole-filet samples collected at the conclusion of the experiment. All fish survived the study, and we observed no differences in growth, condition, or Hg concentration among control and biopsy treatments. Hg concentrations from non-lethal biopsies were moderately correlated with whole-filet concentrations. Our findings suggest that minimally invasive muscle biopsies can provide representative Hg concentration data without detectable negative effects on fish performance, supporting their application in conservation physiology, longitudinal biomonitoring and contaminant studies involving small-bodied salmonids.