McGrouther's Cusk, <i>Diancistrus mcgroutheri</i> Click to enlarge image
The 36mm SL holotype (male) of McGrouther's Cusk, caught at a depth between 30m and 60m, Holmes Reef, Coral Sea. The fish is held in the fish collection of the Western Australian Museum (WAM P. 29627-047). Image: Peter Moller
© Peter Moller

Fast Facts

  • Classification
  • Size Range
    The species grows to about 6 cm in length.


McGrouther's Cusk is a small tropical species that lives deep within the coral. The species looks very similar to other cusks in the genus Diancistrus and separating usually requires the use of a microscope and specialist papers.


McGrouther’s Cusk was described in a 2005 paper by Schwarzhans, Møller & Nielsen. The authors described 26 new species in the paper, which reviewed the dinematichthyine fishes of the Indo-West Pacific.

Fishes in the genus Diancistrus all look very similar, with long-based dorsal and anal fins, and a free rounded caudal fin. They have uniform live coloration, primarily yellow, orange, red or brown.

McGrouther’s Cusk has small eyes (1.5% to 2.1% of SL), a slender head profile, no scales on the operculum but a narrow scale patch on the cheek. Additional characters that separate the species from other Diancistrus are the pseudoclaspers of the males. The inner pseudoclasper forms a sharp, forward-inclined thorn or lobe. The outer pseudoclasper has a short, ear-lobe shaped extension.

The species was named after Australian Museum fish collection manager, Mark McGrouther.


Fishes in the genus Diancistrus live deep within the recesses of coral reefs. They are less commonly found in lagoons and are rare in tide pools or rocky shores. Few specimens were registered in fish collections before the invention of scuba diving and the use of ichthyocides for the collection of fishes. Since then, large numbers of these fishes have been collected which suggests that they play an important role in the ecology of coral reefs.


McGrouther’s Cusk occurs in inshore and coral reef waters. It is known from the Coral Sea Islands of northern Queensland and Papua New Guinea.

The map below shows the Australian distribution of the species based on public sightings and specimens in Australian Museums. Click on the map for detailed information. Source: Atlas of Living Australia.


  1. Hoese, D.F., Bray, D.J., Paxton, J.R. & G.R. Allen. 2006. Fishes. In Beesley, P.L. & A. Wells. (eds) Zoological Catalogue of Australia. Volume 35. ABRS & CSIRO Publishing: Australia. parts 1-3, pages 1-2178.
  2. Schwarzhans, W., Moller, P.R. & Nielsen, J.G. (2005). Review of the Dinematichthyini (Teleostei: Bythitidae) of the Indo-West Pacific. Part I. Diancistrus and two new genera with 26 new species. The Beagle. Records of the Museum and Art Gallery of the Northern Territory. 21: 73–163 [129, figs 17, 45, 46].