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Revillagigedo Archipelago and Clipperton atoll are oceanic islands located in the eastern tropical Pacific. The composition and trophic structure of their fish assemblages have never been characterized in detail, and the aim of this study was therefore to analyse the community structure and assess the similarity of fish assemblages between these two areas. Underwater visual fish censuses were conducted using band transects at two depth levels in three islands of the Revillagigedo Archipelago (Socorro, San Benedicto, and Roca Partida) and at Clipperton atoll. We calculated ecological indices (density, richness, Shannon diversity, Pielou evenness, and taxonomic distinctiveness) for each transect. These were compared in order to determine quantitative differences among the islands and bathymetric levels. Qualitative analyses (ANOSIM, nMDS, and SIMPER) were also performed. Finally, we analysed the trophic structure of the assemblages and the functional diversity of the four studied sites. The results showed significant differences for all indices, except diversity (H′). Roca Partida was the site with greatest abundance and richness due to the presence of pelagic species in large numbers. No significant differences were found in functional diversity, suggesting a high degree of ecological redundancy. Lower‐level carnivores with mean trophic level values of between 3.3 and 3.8 dominated both areas. The ordination analysis did not show a clear difference in fish composition among the islands, although Clipperton atoll has a particular fauna characterized by endemic species (Thalassoma robertsoni and Stegastes baldwini). In conclusion, the fish communities of the studied areas seem quite similar, but their assemblage structure differs. In particular, Clipperton is differentiated by the influence of endemic species.

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This paper presents an updated checklist of cartilaginous and bony fishes from the Revillagigedo Archipelago reefs and nearby areas (Tropical Eastern Pacific). To compile this list, we gathered data from field surveys between 1994 and 2015, from an exhaustive literature review, and by consulting museum collections and databases. With these records we estimated the completeness of the local fish inventory using four non-parametric rarefaction methods. We report a total of 389 species in 102 families; 235 of these are reef fish that occur in the Eastern but also in the Central Pacific, and 13 species were identified as endemic to the archipelago. A non-parametric statistical model predicts that the expected number of reef fish present at Revillagigedo should be 244.3 ± 3.2 species, which is 9 species more than the observed richness, and this difference was statistically significant (p = 0.02). That predictive model estimates that about 96% of the total richness of reef fish from the archipelago is known. Comparisons of the completeness of the inventory at Revillagigedo to that reported for the fish fauna of the Eastern Pacific and worldwide, showed that the quality of the sampling effort is remarkably high, in spite of the geographic isolation of the archipelago.