Bony-eared assfish

{{Short description|Species of fish}}

{{Speciesbox

| fossil_range = Holocene

| name = Bony-eared assfish

| image = Acanthonus armatus.jpg

| image_caption = Specimen from north of New Guinea{{cite book|last1=Günther|first1=Albert|title=Report on the Deep-Sea Fishes collected by H.M.S. Challenger during the years 1873-1876|date=1887|pages=117–118; [https://www.biodiversitylibrary.org/page/15501399 Pl. 34], fig. A|chapter=Acanthonus armatus|series=Report on the Scientific Results of the Voyage of H.M.S. Challenger During the Years 1873–76|volume=Zoology—Vol. XXII|chapter-url=https://www.biodiversitylibrary.org/page/15501059}}

| image2 = Memoirs of the Museum of Comparative Zoölogy Vol 24 Plate F (Fig 3).jpg

| image2_caption = Specimen from south of Panama{{cite journal |last1=Garman |first1=S. |title=Reports on an exploration off the west coasts of Mexico, Central and South America, and off the Galapagos Islands, in charge of Alexander Agassiz, by the U. S. Fish Commission steamer Albatross, during 1891, Lieut. Commander Z. L. Tanner, U. S. N., Commanding. XXVI. The Fishes |journal=Memoirs of the Museum of Comparative Zoölogy, at Harvard College |date=1899 |volume=24 |pages=170–171; [https://www.biodiversitylibrary.org/page/28865385 Pl. F], Fig 3 |url=https://www.biodiversitylibrary.org/page/30644803}}

| status = LC

| status_system = IUCN3.1

| status_ref = {{cite iucn |author=Knudsen, S. |date=2015 |title=Acanthonus armatus |volume=2015 |page=e.T190201A60796787 |doi=10.2305/IUCN.UK.2015-4.RLTS.T190201A60796787.en |access-date=19 November 2021}}

| authority = Günther, 1878{{Cite journal |last=Günther |first=Albert |date=1878 |title=Preliminary Notices of Deep-Sea Fishes collected during the Voyange of H.M.S. 'Challenger' |url=https://www.biodiversitylibrary.org/page/25173090 |journal=The Annals and Magazine of Natural History |volume=2 |issue=7 |pages=22–23 }}

| genus = Acanthonus

| species = armatus

| synonyms = {{Species list

|Acanthonus spinifer|Garman, 1899

}}

| synonyms_ref = {{cite journal |last1=Nielsen |first1=Jørgen G. |title=On the genera Acanthomus and Typhlomus (Pisces, Brotulidae) |journal=Galathea Report |date=1965 |volume=8 |pages=32–48 |url=https://digit.snm.ku.dk/Documentsonline/GalatheaReports/galathea-vol.08-pp_032-048.pdf}}

}}

The bony-eared assfish (Acanthonus armatus) is a bathypelagic species of cusk-eel found in tropical and sub-tropical oceans at depths of from {{convert|1171|to|4415|m|ft}}. It has been found as far north as Queen Charlotte Sound off British Columbia's coast.{{Cite web |url=http://www.cbc.ca/news/canada/british-columbia/assfish-royal-bc-museum-display-1.3404806 |title=Assfish goes on display at the Royal B.C. Museum in Victoria |last=Fuhrmann |first=Mike |date=14 January 2016 |publisher=CBC News |access-date=15 January 2016}} This species grows to a length of {{convert|37.5|cm|in}} standard length.{{FishBase |genus=Acanthonus |species=armatus |year=2014 |month=January}} The larvae are similar in overall form to the related gargoyle cusk, but have elongated 3rd, 4th, and 5th pectoral-fin rays.{{Cite journal |last1=Girard |first1=Matthew G. |last2=Nonaka |first2=Ai |last3=Baldwin |first3=Carole C. |last4=Johnson |first4=G. David |date=2024 |title=Discovery and description of elaborate larval cusk-eels and the relationships among Acanthonus, Tauredophidium, and Xyelacyba (Teleostei: Ophidiidae) |url=https://doi.org/https://doi.org/10.7755/PP.24.3 |journal=Early Life History and Biology of Marine Fishes: Research Inspired by the Work of H Geoffrey Moser |language=en |pages=20–42 |doi=10.7755/pp.24.3|doi-access=free }}

The bony-eared assfish is by some sources believed to have the smallest brain-to-body weight ratio of any vertebrate.{{Cite journal |last1=Fine |first1=M. L. |last2=Horn |first2=M. H. |last3=Cox |first3=B. |date=23 March 1987 |title=Acanthonus armatus, a deep-sea teleost fish with a minute brain and large ears |jstor=36061|journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=230 |issue=1259 |pages=257–265 |doi=10.1098/rspb.1987.0018 |issn=0080-4649 |pmid=2884671|bibcode=1987RSPSB.230..257F |s2cid=19183523 }}{{Dubious|Introduction|reason=The vertebrate with the smallest brain to body mass ratio is the Ocean sunfish, not the Bony-eared assfish, which is even beaten by cetaceans like the blue whale.|date=January 2025}}

Like many other creatures that dwell in the depths of the sea, assfish are soft and flabby with a light skeleton. This is likely to have resulted from a lack of food and the high pressures which accompany living at such a depth, making it difficult to generate muscle and bone.{{cite web |last=Langley |first=Liz |date=2016-03-12 |title=What'd You Call Me? Meet the Bony-Eared Assfish |work=National Geographic |url=https://www.nationalgeographic.com/animals/article/160312-animals-assfish-weird-names-science-oceans |archive-url=https://web.archive.org/web/20220114164357/https://www.nationalgeographic.com/animals/article/160312-animals-assfish-weird-names-science-oceans |url-status=live |archive-date=January 14, 2022 |access-date=27 March 2025}}