Telmatherina is a genus of small sailfin silversides endemic to the Indonesian island of Sulawesi, grouped with the rainbowfish order even though its family sits apart from the true Australian-New Guinean Melanotaeniidae rainbowfish. The atlas covers 10 species, from about 2 in up to 3.5 in, all restricted to Sulawesi's streams, rivers, and, for several species, the ancient tectonic lakes of the Malili system, one of the world's classic natural laboratories for studying rapid, in-place species diversification. Males typically carry the elongated, sail-like dorsal and anal fins and bright iridescent color that give the group its common name.
Several species reach the aquarium hobby as Sulawesi rainbowfish or sailfin silversides, prized for their slender build, shimmering blue or yellow highlights, and the dramatic finnage of mature males in species such as Telmatherina bonti and T. sarasinorum, though most need harder, more mineral-rich water than typical rainbowfish to thrive and breed well. The conservation picture is serious: seven of the ten species are rated Near Threatened and two Endangered, consistent with a genus whose entire range sits inside a small, heavily pressured set of Sulawesi lake and river systems facing habitat disturbance and introduced fish.