Freshwater mussels (Bivalvia, Unionida) play a crucial role in freshwater environments as benthic ecosystem engineers, providing essential ecosystem services. Their sedentary, filter-feeding life history also makes them valuable indicators of environmental change. Despite their benefits, mussels are among the most imperiled taxonomic groups globally, making investigations into poorly understood mussel necessities like diet imperative for conservation efforts. Natural history collections represent an underutilized resource for addressing long-term ecological questions. Molecular analyses of archived mussel collections offer a unique opportunity to compare past and present dietary patterns, providing valuable insights into long-term ecological change and historical environmental conditions. However, the effects of tissue preservation method on dietary tracers such as fatty acids (FA) remain unknown. In this study, we assess how common preservation methods affect FA profiles in two freshwater mussel species. Specifically, we identify and quantify baseline FA signatures, evaluate FA differences among preservation techniques, and explore approaches for developing preservation-specific FA correction factors. Preliminary results show FA composition and retention time differences between three preservation methods relative to the recommended freeze-dry baseline. The oven-dry method deviated the least from the baseline, ethanol preservation deviated further from the baseline, and formalin preservation deviated the most from the baseline. Results also suggest differences in FA profile composition between the two species at one site. This work provides the needed baseline information to improve the reliability of FA-based dietary analyses in preserved mussel specimens. By addressing methodological uncertainty associated with archived tissues, this study enhances the potential for historical collections to be used in reconstructing mussel diets and ecological change through time.