The northern yellow-black triplefin (Enneapterygius gracilis), also known as the northern Australian yellow-black triplefin, is a species of triplefin blenny in the genus Enneapterygius. It was described by German Ichthyologist Ronald Fricke in 1994.[1] It is a tropical blenny, endemic to northern Australia, in the western Pacific and southeastern Indian Oceans.[2] It is a non-migratory species which dwells in shallow tidal pools on coralline rock and in seagrass, and has been recorded swimming at a depth range of 0-.[2] Male northern yellow-black triplefins can reach a maximum length of 2.8 centimetres (1.06 inches).[2]