Scorpaena onaria Jordan & Snyder (Scorpaeniformes: Scorpaenidae), previously known only from the northwestern Pacific Ocean, is reported from the southwestern Pacific Ocean for the first time on the basis of 19 specimens. The southwestern Pacific specimens are regarded as a southern population of S. onaria, characterised by a shorter supraocular tentacle and larger body size compared with the northwestern Pacific specimens. The southern population is described in detail including comparisons with all known Indo-Pacific species of the genus Scorpaena. Analyses of 37 measurements of the southern population of S. onaria found that relative orbit diameter and second anal-fin spine length became significantly smaller with growth. Initially cycloid, the scales enclosed by the posterior tips of the upper and lower opercular spines and opercular mar-in change to ctenoid with growth at c. 160-170 mm standard length. A mature female differed from an immature female and males in having a longer upper jaw, steeper dorsal profile of the snout. and shorter nasal spine. As a consequence, the species previously reported as S. neglecta from the Andaman Sea and northwestern Australia was reidentified as S. onaria.
