Within low nutrient tropical oceans, islands and atolls with higher primary production support higher reef fish biomass and reef organism abundance. External energy subsidies can be delivered onto reefs via a range of physical mechanisms. However, the influence of spatial variation in primary production on reef fish growth and condition is largely unknown. It is not yet clear how variability in food delivery onto a reef interacts with reef depth and slope, and affects reef fish productivity. Here we test the hypothesis that with increased proximity to deep-water oceanic allochthonous nutrient sources, or at sites where transportation of these water bodies onto reefs is facilitated by shallower reef slopes, parameters of fish growth and condition will be higher, and this pattern will be further emphasised in areas naturally higher in primary production. Contrary to expectations, we found no association between fish growth rate and sites with higher mean chlorophyll values. There were no differences in δ¹⁵N or δ¹³C values in fish collected at greater depths across reefs, suggesting a homogeneous primary production resource. However, the relationship between fish condition and primary production was influenced by depth of collection, driven by higher fish condition at shallow depths within a study site which is a ‘hotspot’ of primary production. Carbon δ¹³C values were depleted at sites with increasing primary production, and this trend was reversed by an interactive effect with shallower reef slopes. Our results indicate that deep-water ocean nutrient influences did not translate into observable increases in overall population growth in planktivorous Chromis fieldi within the 10–17.5 m depth range, but show the importance of site specific variation in hydrodynamics and reef physical characteristics influencing fish carbon isotopic composition and condition.