Identifying the sources of methylmercury (MeHg) and tracing the transformations of mercury (Hg) in the aquatic food web is an important component of effective strategies for managing fish Hg concentrations. In our previous work we measured stable isotopes of Hg (δ202Hg, Δ199Hg, and Δ200Hg) in the Laurentian Great Lakes and estimated source contributions of Hg to bottom sediment. Here, we identify isotopically distinct Hg signatures for Great Lakes predatory fish. Fish reflect high values for odd-isotope mass independent fractionation (MIF) that span a large range in Δ199Hg (2.27 - 6.73‰). With the exception of Lake Erie, temporal variability and intralake specific signatures were not evident. The large range in odd-MIF reflects variability in the depth of the euphotic zone where Hg is most likely incorporated into the food web. Even-isotope MIF, a potential tracer for Hg from precipitation, appears both disconnected from lake sedimentary sources and comparable in magnitude among the lakes. When comparing isotopic Hg signatures in sediment and MeHg in fish, bioaccumulated MeHg isotopic signatures are more reflective of atmospheric precipitation than sediment. We also conclude that the degree of photochemical processing of Hg is controlled by phytoplankton uptake rather than by dissolved organic carbon quantity among lakes.