Bovictus diacanthus, the Tristan klipfish, is a species of marine ray-finned fish, a temperate icefish or thornfish, belonging to the family Bovichtidae.

Bovichtus diacanthus was first formally described in 1819 as Callionymus diacanthusby the Scottish botanist and officer in the British Army Dugald Carmichael with the type locality given as Tristan da Cunha in the South Atlantic,[2] When Achille Valenciennes described the genus Bovichtus in 1832 the only species he classified within the new genus was Carmichael's C. diacanthus which is therefore the type species of Bovichtus.

They have a single lateral line and the anterior dorsal fin is spiny and starts above the operculum.

[5] They are normally mottled in colour and their gill membranes direct the exiting water upwards, an adaptation for a sedentary benthic lifestyle.

[7] Bovichtus diacanthus is restricted to the waters around Tristan da Cunha and Gough Island in the South Atlantic Ocean.