The Mirror Butterflyfish or Oval-spot butterflyfish, Chaetodon speculum, is a species of butterflyfish (family Chaetodontidae). It is found in the Indian and Pacific Oceans from Indonesia to Japan and south to the Great Barrier Reef and Papua New Guinea. The species has also been reported from Madagascar, Mauritius and Reunion.
It grows to a maximum of 18 cm (7 in) in length. The body color is a bright to orange-yellow with a big black blotch below the dorsal fin and a vertical black bar running through the eye.
Like the other butterflyfishes with angular yellow bodies with black eyestripes and a single differently-colored patch (except in the quite basal Blue-lashed Butterflyfish, C. bennetti), it belongs in the subgenus Tetrachaetodon. Among this group it seems to be particularly close to the Zanzibar Butterflyfish (C. zanzibarensis) which has a smaller black blotch and traces of horizontal stripes on the flanks. If Chaetodon is split up, the subgenus Tetrachaetodon would be placed in Megaprotodon.
The Mirror Butterflyfish is found in coral reefs at depths between 3 and 30 m. It favors coastal reef slopes rich in hydroids and sea anemones. Small juveniles hide in coral thickets. Usually, this species is solitary and relatively uncommon. They feed on coral polyps and invertebrates.