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Species' niche depends on several ecological and evolutionary factors. Phylogenetically close species may present niche conservatism, retaining their ancestral ecological characteristics. Alternatively, in a situation of limited resources, species can differentiate themselves through changes in their ecological and morphological characteristics to reduce niche overlap, thus facilitating coexistence. In this study, we investigated the ecological niche of two phylogenetically closely related cryptobenthic reef fish species that co-occur in the southern Brazilian coast, Parablennius pilicornis and P. marmoreus. We examined possible overlap in three niche dimensions (thermal, spatial and trophic) to verify if species hold phylogenetic niche conservatism or are partitioning some niche dimension. For this, we studied their densities, microhabitat affinities and diets among four rocky reefs of southern Brazil. The two species presented differences in thermal distribution, and their abundance differed according to depth strata, but no differences were found for microhabitat preferences. They also presented a similar omnivorous diet, with crustaceans and algae as main prey types. The Pianka's niche overlap values did not differ from the values expected in the null model for thermal and depth, and it was higher than expected by chance for microhabitat and diet. Considering all the niche dimensions analysed together, the total niche overlap was greater than expected at random. These results suggest that the two species are successfully coexisting despite considerable niche overlap. Thus, their coexistence may not depend on the evolution of divergent patterns of resource use, but on the evolutionary history of the species., Author(s): Angela M. Canterle [sup.1] , Lucas T. Nunes [sup.1] , Luiz G. R. Oliveira-Santos [sup.2] , Sergio R. Floeter [sup.1] Author Affiliations: (1) grid.411237.2, 0000 0001 2188 7235, Marine [...]