West Australian butterflyfish (Chaetodon assarius)

Classification (WoRMS)

Full classification as recorded by WoRMS: Kingdom: Animalia · Phylum: Chordata · Class: Teleostei · Order: Acanthuriformes · Family: Chaetodontidae · Genus: Chaetodon.

Accepted name: Chaetodon assarius · Authority: Waite, 1905 · Taxonomic status: accepted · AphiaID: 273325.

Source: World Register of Marine Species (WoRMS) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=273325 (CC BY 4.0). Accessed 2026-09-25.

Biology and life history (FishBase)

Measured values published by FishBase for Chaetodon assarius. Only fields the database actually holds for this species are shown; these are database values, not aquarium guidance.

Maximum length: 13 cm · Depth range: 1–40 m · Habitat zone: reef-associated · Body shape: short and / or deep · Vulnerability index: 10 of 100 · Aquarium trade: never/rarely.

FishBase notes: Inhabits rocky reefs and sandy-weed flats (Ref. 3132). Occurs in aggregations (Ref. 9710). Feeds on algae and zooplankton.

Oviparous (Ref. 205). Form pairs during breeding (Ref. 205). Recently discovered in deep water in cold upwelling areas of Bali (Ref. 9710). Unknown to American and European aquarists although can easily be maintained in a tank according to Australian aquarists.

Source: FishBase species summary (SpecCode 6516) — https://www.fishbase.se/summary/Chaetodon-assarius.html (CC BY-NC 3.0 — non-commercial use only). Accessed 2026-09-25.

Distribution and occurrence records (GBIF)

406 georeferenced occurrence records for Chaetodon assarius are published through GBIF from 1 countries or marine areas. The map above plots 45 distinct locations from a sample of 406 records, omitting 5 inland records that carry an institution's coordinates rather than a collection site; it shows where the species has been observed and reported, not a modelled range.

Most records by country or area: Australia (406).

Source: GBIF Occurrence Search (taxonKey 2385498) — https://www.gbif.org/occurrence/search?taxon_key=2385498&has_coordinate=true (records CC0 / CC BY); WoRMS distribution records (MarineRegions) — https://www.marinespecies.org/aphia.php?p=taxdetails&id=273325 (CC BY 4.0); Natural Earth 110m basemap — https://www.naturalearthdata.com/ (public domain). Accessed 2026-09-25.

Conservation status (IUCN Red List)

The IUCN Red List assesses Chaetodon assarius Waite, 1905 as Least Concern (code LC). No trend, population estimate or threat analysis is given here, because none is available from this source without the Red List API; follow the source link for the full assessment, including its date.

Source: IUCN Red List of Threatened Species (taxon 165710) — https://www.iucnredlist.org/species/165710/0; GBIF IUCN Red List category endpoint (taxonKey 2385498) — https://api.gbif.org/v1/species/2385498/iucnRedListCategory. Accessed 2026-09-25.

Description and natural history (Wikipedia)

The West Australian butterflyfish has a pale silvery-brown coloured body with a vertical dark band running through the eye. The upper two thirds of the body are marked with 5 vertical lines of close-set dots. There is a wide brown to blackish vertical band running across the caudal peduncle and then horizontally along the anal fin.

The juveniles have an obvious black ocellus with white margins at the corner of the soft rayed part of the dorsal fin, this is retained in young adults but is lost as they age. The spiny part of the dorsal fin holds 12–13 spines while the soft-rayed part has 21–22 rays and the anal fin has 3 spines and 18–19 soft rays. This species attains a maximum total length of 15 cm.

The West Australian butterflyfish is endemic to Western Australia where it is found along the southern and western coast from southeast of Israelite Bay to Exmouth Gulf and the North West Shelf. it has recently been claimed to have been found in deep water in cold upwelling areas off Bali, but this is thought to be based on misidentified Chaetodon guentheri.

The West Australian butterflyfish is found over rocky reefs and sandy flats with growth off weed. It occurs in aggregations and feeds on algae and zooplankton. It is an oviparous species which forms pairs to spawn.

The West Australian butterflyfish was first formally described in 1905 by the Australian ichthyologist Edgar Ravenswood Waite (1866–1928) with the type locality given as between Fremantle and Houtman Abrolhos. The specific name assarius means "browned", a reference to the colour and the griddle like markings. Some authorities make this species incertae sedis within the genus Chaetodon but others place it in the subgenus Exornator.

Source: Wikipedia: West Australian butterflyfish — https://en.wikipedia.org/wiki/West_Australian_butterflyfish (CC BY-SA 4.0). Accessed 2026-09-25.