At Réunion Island (south-western Indian Ocean), artificial reefs were submerged in 2003 in a bay and were soon colonised by fish, among which were the highly abundant commercial species Lutjanus kasmira, Priacanthus hamrur and Selar crumenophthalmus. The high concentration and diversity of fish around the artificial reefs is surprising, considering the low abundance of potential benthic prey. We investigated the diet and food partitioning between the aforementioned species using stomach content and stable isotope analyses (δ13C, δ15N). Priacanthus hamrur and S. crumenophthalmus fed on a larger prey diversity and showed significant overlap in their diets, with crustacean larvae the dominant prey. Fish larvae dominated L. kasmira's diet, and δ15N values confirmed the species’ higher trophic level. Differences in δ13C between P. hamrur and S. crumenophthalmus indicated niche segregation, probably as a way to reduce competition, with P. hamrur being characterised by a smaller δ13C range and exhibiting a smaller isotopic niche than S. crumenophthalmus. There was a significant correlation between δ15N and fish standard length for the three species, suggesting that ontogeny partially explained the niche breadth. There was also a significant correlation between δ13C and length for L. kasmira, whereas individual specialisation was prevalent in S. crumenophthalmus.