Megalampris keyesi is an extinct opah from the late Oligocene of New Zealand about 26 million years ago.

The species is named in honour of the New Zealand palaeontologist Ian Warwick Keyes (1938-2004).

It is the largest fossil teleost fish from New Zealand, the spectacular remains comprise three large limestone blocks containing mostly caudal skeleton.

Comparison with the skeletons of living Lampris species suggest the giant fish was around 4 metres (13 ft) in length when alive, which is twice the length of the largest living opah species, Lampris guttatus.

[1] The cleithra in the fossil are significantly enlarged to suggest that Megalampris used the pectoral swimming mode characteristic of moonfishes.