Oplopomops diacanthus about 5 cm long at Big Vicki's Reef, Lizard Island.
Doug Hoese was not able to identify this fish from the photo (iNaturalist, Feb 2019). He says it is a very good colour match for Hazeus diacanthus and also similar to an undescribed Favonigobius from Lizard Island. Hazeus has a thickened and stiff spine at the beginning of the first and second dorsal fin. The full resolution version of this photo shows that not to be the case and shows only 6-7 rays in the first dorsal fin. This rules out Hazeus and suggests Favonigobius. Thanks Doug and Amada Hay!
© Anne Hoggett