ABSTRACT: We provide the first assessment for a coral reef fish population of a potentially threatened endemic species from a remote and isolated oceanic island. Based on a 3-dimensional (3D) numerical field model of the reef habitat and underwater visual censuses conducted by 2 different teams in February and May 2016, we show that the 3.7 km$^\textrm2$ of the Clipperton Atoll reefs shallower than 30 m host >50000 ind. (average density of 0.02 ind. m$^\textrm-2$) of the endemic Clipperton angelfish \textitHolacanthus limbaughi. Based on limited submersible observations to 150 m, the population likely extends below the 30 m depth stratum, resulting in an even larger population size and providing a potential depth refuge against expected warming ocean temperatures.