Pupil shape plays a pivotal role in visual ecology. In taxa such as mammalian herbivores, anurans (frogs), and snakes, previous research has established linkages between pupil shape and ecological niche. However, systematic assessment of pupil shape diversity and their association with niches in freshwater fish is limited. This study investigates interspecific variation in pupil shape and its niche relationship of freshwater stream fish, encompassing over 20 families, 90 genera, 500 species, and approximately 1500 photographic records of individual fish specimens. This study surveyed image-based records from online platforms (e.g., iNaturalist, Joel Sartore’s Photo Ark, state and federal agency sites), field guides, and primary literature. In addition, feeding group assignments were made using the open source FishTraitsDatabase. For each species, a minimum of three and a maximum of five individual images were assessed. Species-level pupil shape was assigned using a majority rule, whereby a shape was recorded if at least two of three individuals shared the same form. A total of six pupil shapes were identified such as circular, anteriorly elliptical (oval & almond shape), dorso-ventrally elliptical, antero-posteriorly elliptical, etc., with the oval shape occurring at the highest frequency. Stacked bar plots showed greater pupil-shape diversity in species preferring moderate current speeds compared to fast or slow currents. Species exhibiting egg-guarding behavior predominantly had almond-shaped pupils. Pearson’s Chi-square and Monte Carlo Fisher’s Exact tests confirmed significant associations between pupil shape and trophic ecology, habitat preference, and reproductive ecology. Additionally, Multiple Correspondence Analysis indicated that specific pupil shapes clustered with particular ecological niches. Notably, pupils with vertices in the anterior position (almond shape) tended to be associated with fast current stream predators. This study shows that the pupil shape categories provide a useful framework for characterizing ecological niches in freshwater fish. Results suggest that pupil shape is functionally associated with habitat preference and trophic ecology in fishes.