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Climate-driven decreases in body size have been documented for a variety of taxa and proposed as a universal response to climate change. However, empirical support among taxa, including fishes, has been mixed, with some fishes growing larger at higher temperatures, and causal mechanisms for faster or slower growth under debate. We simulated effects of climate warming on bluegill (Lepomis macrochirus) growth and consumption and used linear regression and boosted regression trees (BRTs) to model length-at-age for bluegill from Michigan lakes from 1945 to 2019. Bioenergetics models showed bluegill growth and consumption both increase under climate warming. In contrast, linear regression revealed that bluegill ages 1–4 decreased (–0.20 to –0.55 mm/year) in mean length-at-age and that ages 5–8 increased or did not statistically change. BRTs demonstrated that growth had a unimodal relationship with surface water temperature and degree days, peaking at intermediate values. This mismatch between simulations and empirical data may be from increased recruitment leading to increased food limitation at higher temperatures. Future research should empirically test this hypothesis and assess the consequences for ecosystem functions and services.