Abstract Intraspecific niche variation shapes the structure and function of food webs, but we still know little about the magnitude and drivers of trophic variation within species in species‐rich communities. Here, we examined how intrinsic (sex and life stage) and extrinsic (locality and season) factors affect the diet composition and trophic niche width of tropical fish species. Specifically, we studied co‐occurring species with benthopelagic ( Stellifer ericymba , S. melanocheir , S. zestocarus , and Larimus argenteus ) and benthic feeding habits ( S. strabo , Cathorops manglarensis , Notarius troschelii , and Urotrygon rogersi ) on the central Pacific coast of Colombia. Overall, we observed strong spatial and seasonal effects driving variation in the consumption of (i) amphipods, copepods, and decapods for benthopelagic species and (ii) mollusks and polychaetes for benthic species. As expected, we observed little sexual diet variation; however, surprisingly, most species showed little ontogenetic diet variation. Seasonality strongly shaped the trophic niche width for most species, but effects were species‐specific, suggesting no general pattern of seasonal niche expansion across species. In turn, spatial effects on the trophic niche width were congruent across species, which might be related to differences in the diversity of available resources between bays. Our results reveal the complex interplay between intrinsic and extrinsic factors in shaping resource exploitation by coastal fish. This high level of trophic plasticity may be a critical component for both the persistence of marine populations and the stability of local food webs. Abstract in Spanish is available with online material.