Taxonomic Status of Nominal Species of the Long-Fin Herring Genus Ilisha Previously Regarded as Synonyms of Ilisha megaloptera (Swainson, 1839) (Teleostei: Clupeiformes: Pristigasteridae)

Numerous specimens of long-fin herrings (ilishas), previously identified as Ilisha megaloptera (Swainson, 1839) because of their asymmetrical swimbladder, deep body, and few ventral scutes, were examined and found to represent three valid species: Ilisha motius (Hamilton, 1822) (frequently treated as a nomen dubium; distributed in rivers flowing into the Bay of Bengal), true I. megaloptera (eastern coast of India to Andaman Sea), and Ilisha russellii (Bleeker, 1852) (previously regarded as a junior synonym of I. megaloptera; distributed from Malacca Strait to Borneo). Each species is redescribed in detail based on specimens collected from throughout the range of each taxon. Due to the highly diverse shape of its swimbladder, the phylogenetic position of I. motius is still unclear. Reference COI “barcode” fragments are currently only available for I. russellii, preventing molecular confirmation.