The common silver-biddy (Gerres oyena), also known as the blacktip silver biddy, Darnley Island silverbelly, longtail silverbiddy, oceanic silver biddy, shining silver-belly or slender silver belly, is a species of mojarra native to marine and brackish waters of coastal waters of the Indian Ocean and the western Pacific Ocean. It inhabits estuaries, coastal waters and lagoons. This species can reach a length of 30 cm (12 in), though most do not exceed 20 cm (7.9 in). This species is important to local commercial fisheries.