Environmental Context. Surveys to assess the body burden of mercury in fish to support research or contamination advisory programs typically involve capturing and killing fish and analyzing muscle tissue for mercury. Lethal sampling may not be feasible in protected waters or in studies involving threatened or endangered species. We analyzed tail fin samples of two fish species for total mercury and compared results with muscle-tissue mercury and concluded that fin-Hg can be used as a predictor of muscle-Hg. This approach enables catch and release studies for mercury in fish. Abstract. The caudal (tail) fins from 17 walleye (Sander vitreus) and 12 northern pike (Esox lucius) from three northern Arizona lakes (Long Lake, Soldier Lake, and Upper Lake Mary) were analyzed for total-Hg by combustion–atomic absorption spectrometry. Results indicate that the fin contains measurable Hg that correlates with muscle-Hg concentrations. As the body burden of Hg increased, the concentration in the fin increased relative to the muscle. Mercury concentrations also increased with fish length and weight, although the relationship was lake- and species-dependent. Fish from Soldier Lake had the most efficient uptake of Hg, likely due to the trophic structure of the lake or the condition of the fish, but possibly due to an acute source of Hg. Overall, this study demonstrates that caudal fin clippings can be used as a non-lethal predictor of muscle-Hg concentrations, which can reduce the number of fish killed in routine monitoring programs.