Western Butterflyfish, Chaetodon assarius Waite 1905

Other Names: Assarius Butterflyfish, West Australian Butterflyfish

A Western Butterflyfish, Chaetodon assarius, at the Houtman Abrolhos islands, Western Australia. Source: Graham Edgar / Reef Life Survey. License: CC by Attribution

A pale silvery-brown butterflyfish with a dark band through the eye, five vertical lines of close-set spots on the upper 2/3 of the body, and a broad brown to blackish band crossing the caudal peduncle and extending forward along anal fin. Juveniles have a distinct white edged black ocellus at the angle of the soft dorsal fin, persisting in young adults.

The Western Butterflyfish is known mostly from trawls in the southern part of its range.

Cite this page as:
Bray, D.J. 2016, Chaetodon assarius in Fishes of Australia, accessed 17 Jun 2024, https://fishesofaustralia.net.au/Home/species/2373

Western Butterflyfish, Chaetodon assarius Waite 1905

More Info


Endemic to Western Australia, from SE of Israelite Bay, to Exmouth Gulf and the Northwest Shelf. Sometimes aggregates in small numbers on reefs. Unverified reports from Bali, Indonesia, are most likely misidentifications of Chaetodon guentheri (Allen et al. 1998).


Dorsal fin XII–XIII, 21–22; Anal fin III, 18–19; Caudal fin 17; Pectoral fin 14–15; Pelvic fin I, 5; Lateral line scales 37–43; Gill rakers ~17.

Body very deep (58-62% SL), short, strongly compressed; caudal peduncle shallow. Head small (30-31% SL); snout slightly produced and tapered; snout slightly produced and tapered; eyes large (34-36% HL); mouth very small; jaws with bands of bristle like teeth; gill rakers small, but normally developed.
Scales ctenoid, firmly attached, covering body, most of vertical fins and pectoral fin bases, those on body much larger than those on fins; lateral line following contour of back. 
Single elongate dorsal fin with little separation between spines and segmented rays, first spine small, second about twice length of first, third and subsequent spines progressively longer, rays in front half of soft portion becoming progressively longer, those in rear half becoming progessively shorter providing a vertical posterior edge; anal fin much smaller than dorsal, but similar and opposite posterior portion; caudal fin slightly rounded in juveniles, truncate in adults. Pectoral fins triangular with upper rays longest. Pelvic fins thoracic, large, with first ray extended.


To 13 cm


Silvery with a black band from first dorsal spine to top of eye, then angled to pelvic-fin origin; 5 lines of close set spots on upper 2/3 of body below dorsal-fin base; broad brown to black band crossing caudal peduncle and extending forward along anal fin. Juveniles with distinct white edged black ocellus at angle of soft dorsal fin, persisting in young adults.


Omnivore - feeds on algae and zooplankton.


Taken occasionally as incidental bycatch in commercial trawls in the south.


IUCN Red List of Threatened Species: Least Concern.

Species Citation

Chaetodon assarius Waite, 1905, Rec. Aust. Mus. 6(2): 66. Type locality: between Fremantle and Houtman Abrolhos, Western Australia.


Bray, D.J. 2016


Australian Faunal Directory

Western Butterflyfish, Chaetodon assarius Waite 1905


Allen, G.R. & Gomon, M.F. 2008. Family Chaetodontidae. pp. 608-609 in Gomon. M.F., Bray, D.J. & Kuiter, R.H (eds) Fishes of Australia's Southern Coast.Sydney : Reed New Holland 928 pp.

Allen, G.R., Steene, R. & Allen, M. 1998. A Guide to Angelfishes & Butterflyfishes. Cairns : Odyssey Publishing/Tropical Reef Research 250 pp. figs.

Allen, G.R., Steene, R.C., Human, P. &  DeLoach, N. 2003. Reef fish identification: Tropical Pacific. New World Publications Florida, USA

Allen, G.R. & Swainston, R. 1988. The Marine Fishes of North-Western Australia. A field guide for anglers and divers. Perth, WA : Western Australian Museum vi 201 pp., 70 pls.

Burgess, W.E. 1978. Butterflyfishes of the World. New Jersey : T.F.H. Publications Inc. 832 pp. figs.

Gloerfelt-Tarp, T. & Kailola, P.J. 1984. Trawled Fishes of Southern Indonesia and Northwest Australia. Jakarta : Dir. Gen. Fish. (Indonesia), German Tech. Coop., Aust. Dev. Ass. Bur. 406 pp.

Kuiter, R.H. 1994. Family Chaetodontidae. pp. 625-627, figs 550-551 in Gomon, M.F., Glover, C.J.M. & Kuiter, R.H. (eds) The Fishes of Australia's South Coast. Adelaide : State Printer 992 pp. 810 figs.

Kuiter, R.H. 1996. Guide to Sea Fishes of Australia. A comprehensive reference for divers and fishermen. Sydney, NSW, Australia : New Holland Publishers xvii, 434 pp.

Kuiter, R.H. 2002. Butterflyfishes, Bannerfishes and their Relatives. Chorleywood, U.K. : TMC Publishing 208 pp.

Pyle, R. & Myers, R. 2010. Chaetodon assarius. The IUCN Red List of Threatened Species 2010: e.T165710A6097937. http://dx.doi.org/10.2305/IUCN.UK.2010-4.RLTS.T165710A6097937.en. Downloaded on 24 November 2016.

Sainsbury, K.J., Kailola, P.J. & Leyland, G.G. 1985. Continental Shelf Fishes of Northern and North-Western Australia. Canberra : Fisheries Information Service 375 pp. figs & pls.

Steene, R.C. 1978. Butterfly and Angelfishes of the World. Australia. Sydney : A.H. & A.W. Reed Vol. 1 144 pp. 216 figs.

Waite, E.R. 1905. Notes on fishes from Western Australia. No. 3. Records of the Australian Museum 6(2): 55-82 fig. 23 pls 8-17

Quick Facts

CAAB Code:37365012

Conservation:IUCN Least Concern

Depth:1-40m (to 200m)

Fishing:Aquarium fish (rare)

Habitat:Reef associated

Max Size:13 cm TL


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CAAB distribution map