ABSTRACTDespite the critical conservation status of the endemic gudgeon Gobio insuyanus, its feeding ecology remained unstudied. This research addresses this gap by investigating the diet of G. insuyanus in the Insuyu spring–stream system of Central Anatolia (Turkey) analyzing spatial, temporal, and intraspecific variations. We compared two distinct habitats: a stable spring and its continuum, a fluctuating stream. Results indicate that G. insuyanus is an omnivore, consuming primarily detritus, Gammarids, and Diptera larvae. Feeding intensity was higher in the spring habitat, particularly in summer, possibly related to its stable temperature and lower turbidity. Dietary diversity was higher in the stream, potentially reflecting its greater habitat complexity, but decreased in both habitats in autumn, suggesting a seasonal decline in prey availability. A significant ontogenetic shift in diet was observed; mature individuals exhibited a narrower niche and preferred larger prey, probably due to increased gape size, improved foraging ability, and higher energy requirements. No significant dietary differences were found between the sexes. The results have conservation implications, emphasizing the need to maintain the integrity of both habitats. Future research incorporating fish movement data with feeding ecology will further improve our understanding and inform more targeted conservation strategies.