Atherinops affinis, the topsmelt silverside or simply topsmelt, is a species of Neotropical silverside native to the eastern Pacific Ocean. This fish is found along the west coast of North America from southern British Columbia to Baja California. It is marine and it often schools in relatively shallow water such as estuaries, bays, rocky intertidal zones and kelp forests, where it feeds on zooplankton. This is a common fish of the San Francisco Bay and Sacramento-San Joaquin River Delta in California. The topsmelt is silver, with a shiny silver lateral band running its length, and blue or green coloration dorsally.. Their gills are a golden-yellow. The eyes of the topsmelt are small and beady. Its top lip is folded down. Topsmelts have long pectoral fins compared to other fish. On the jaw of the topsmelt are pointy, small teeth. It is edible and may be fished recreationally. It is the only known member of its genus.