Nesiarchus nasutus, the Black gemfish, is a species of snake mackerel found in tropical and subtropical waters in most parts of the world, though not in east Pacific and north Indian waters. It occurs at depths of from 200 to 1,200 metres (660 to 3,940 ft) though they make diel vertical migrations from benthopelagic to mesopelagic depths at night. This species can reach a length of 130 centimetres (51 in) SL though most do not exceed 80 centimetres (31 in) SL. It is of minor importance to local commercial fisheries. This species is currently the only known member of its genus, Nesiarchus. That genus is thus considered monotypic.