Rapa Nui (Easter Island) is the most isolated inhabited island in the Indo-Pacific, located approximately 3,700 km west of Chile and 2,000 km from the nearest inhabited island, Pitcairn. This isolation led to a very unique fauna surrounding the island. The likelihood of finding never before encountered and endemic species such as today's fish is very high.
Perchlets of the family Anthiadinae are small beautiful fish. Their relatives (e.g. genus Anthias) are very famous in the ornamental fish trade. The name of this new species was given in reference to the beautiful Rapa Nui sunsets. The language is Rapa Nui; the phrase ahiahi-ata means “the last moments of light before nightfall.”
For the experts: A new species of the perchlet genus Plectranthias is herein described from a single specimen found at Rapa Nui (Easter Island) in the South Pacific. Plectranthias ahiahiata sp. n. was collected at a depth of 83 m in a mesophotic coral ecosystem at Rapa Nui. The main difference between Plectranthias ahiahiata and other members of the genus is higher fin-ray counts (X, 18 dorsal; 18 pectoral) and its distinctive coloration. Compared to the three other known eastern South Pacific species, P. ahiahiata has more dorsal-fin rays, more pectoral-fin rays, fewer tubed lateral-line scales, fewer gill rakers, a longer head relative to SL, a very short first dorsal spine relative to SL, and a short third anal spine relative to SL. Plectranthias ahiahiata is distinguished from western Pacific species, by having more dorsal- and pectoral-fin rays. The closest relative based on genetic divergence (with 12.3% uncorrected divergence in the mitochondrial COI gene) is Plectranthias winniensis, a widely distributed species, suggesting important links between Rapa Nui and western Pacific islands. This new species adds to the high endemism of the Rapa Nui ichthyofauna, and is further evidence of the importance of mesophotic reefs as unique communities.