We used stable isotope ratio and gut content analyses to determine and compare the feeding ecology of two commercially important predator species, Lophius piscatorius and Lophius budegassa in the Celtic sea, where data concerning their trophic ecology remain sparse. This study included two areas and two size-classes, showing that anglerfish in the Celtic sea are mainly piscivorous top predators as observed in other marine waters. However, a substantial part of the diet of the fish in the small size classes consists of benthic macro-invertebrates, mainly Crustaceans. Despite the common knowledge that they are opportunistic predators that display a low degree of prey selectivity, our results suggest that the two species have different trophic niches when they occur in the same area. In the shallow area, both small and large individuals of L. budegassa seemed to prefer Crustacean prey, whereas L. piscatorius showed a clear shift from Crustaceans to fish prey with increasing size-class in the two areas. Stable isotope data analysis support the common finding that trophic level increases with body size for L. piscatorius and that overlaps between the isotopic niche spaces are more pronounced in the deeper area. Ecosystem-based approaches to fisheries management requires the development of multi-species modelling based on food web structure and species interactions. Our results emphasize the importance of modelling the two species and size classes separately, as they indicate clear trophic segregation.