There may be many ways to be an herbivorous fish, but it usually takes a lot of guts.

Classic examples of convergent trophic evolution in fishes have focused predominantly on adaptations in craniofacial morphology to piscivorous and durophagous diets. With the physiological demands of nutrient-poor, plant-based diets, adaptation to herbivory also significantly influences digestive physiology and morphology, so convergence onto similar herbivorous phenotypes in elements of postcranial morphology such as body shape and intestinal length might also be expected. Here, we integrate dietary and ecomorphological data, geometric morphometrics and phylogenetic comparative methods to investigate convergence in the body plan of Terapontoidei, an ecomorphologically diverse marine and freshwater fish radiation. We show that while diet has shaped morphology, herbivores have not converged towards distinct morphotypes, instead encompassing much of the broader body shape and size morphospace of Terapontoidei fishes. Significantly longer intestines have, however, remained a constant selective demand for adapting to plant-based diets.