Lookdown fish have laterally flat, reflective bodies with a steep forehead and protruding lower jaw. The silvery coloring comes from guanine pigments. The pigmentation creates the mirror-like body but can be manipulated to highly reflect light or dim the light, depending on what will best camouflage them in the water. On the second dorsal fin, the first rays length extends to reach the deeply forked tail. The common name comes from its peculiar head structure. Juveniles have light, vertical stripes that disappear with age.
