The aim of this study was test whether maximum body length is a reliable predictor of trophic position in freshwater fishes world-wide, and to evaluate alternative models incorporating non-linear relationships and ecological and morphological traits. Using literature and online sources, we compiled a global database of the trophic position, maximum body length, phylogeny (order), biogeographic region, and seven ecological and morphological traits of freshwater fishes (n=2775). We used Bayesian linear mixed effects and Random Forest models, with ten-fold cross-validation, to evaluate whether maximum body size was a reliable predictor of trophic position, or trophic guild (herbivore; omnivore; secondary consumer; top predator). Jaw length was the most influential factor explaining variation in trophic position of freshwater fishes and non-linear models outperformed linear models. Body size-order interactions, caudal fin shape, position of the mouth and whether a species was freshwater obligate, or inhabited lakes or rivers were also significantly correlated with trophic position. However, none of the traits or most parsimonious models met the minimum criteria needed to reliably predict the trophic position, or trophic guild of freshwater fishes. In contrast to assumptions of some food web models, our results suggest that maximum body size alone is a weak predictor of trophic position in freshwater fishes world-wide. Trophic position of freshwater fishes is best described by non-linear relationships, jaw size and phylogenetic interactions with body size.