Grammonus opisthodon, the bighead brotula, is a species of fish known from South Africa.

The dorsal, anal and caudal fins are translucent and continuous with many fine rays.

[4] This fish is known from two nearby sites off the coast of the Eastern Cape of South Africa.

It has been found at a depth of 22 m (72 ft) at Port Alfred and the Storms River Mouth.

[2] Only two specimens have been collected - one prior to 1934 and a second in the early 1980s.This species is currently listed as data deficient by the IUCN as very little is known about it.