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Bluntsnout smooth-head
	Fresh specimen
Conservation status
	; Least Concern (IUCN 3.1)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Alepocephaliformes
Family:	Alepocephalidae
Genus:	Xenodermichthys
Species:	X. copei
Binomial name
	Xenodermichthys copei; (T. N. Gill, 1884)

The bluntsnout smooth-head, black slickhead, Cope's bluntsnout smooth-head, or Atlantic gymnast, Xenodermichthys copei, is a slickhead of the genus Xenodermichthys, found in the Atlantic, Indian, and Pacific oceans, and the Tasman Sea, at depths of 100 to 2,600 m (330 to 8,530 ft). This species grows to a length of 31 centimetres (12 in) TL.

Description

Xenodermichthys copei is a dark-coloured fish that is scaleless, aside from a series of ~60 small, easily missed ring-shaped scales along the lateral line.^[2] It possess 27–30 dorsal fin rays, 28–29 anal fin rays, 7 pectoral fin rays, 6 pelvic fin rays, and 55 caudal rays. It has 48–49 vertebrae.^[2]

The skin is studded with numerous nodular photophores (>500) which are more visible in preserved specimens where skin pigmentation has degraded over time.^[2] The skin of Xenodermichthys possess an unusual system of compartmented sub-dermal spaces filled with a dilute fluid (possibly lymph), thought to serve as a buoyancy aid, alongside scale loss and poor skeleton calcification.^[3] This species lacks a swim bladder.

The photophores of Xenodermichthys have a distinctive reddish-violet hue in fresh specimens under white light, and are underlain with a greenish-blue reflector that lacks guanine. While the greater size of the ventral photophores may indicate their use in counterillumination, the arrangement and structure of the photophores, as well as difficulties in observing bioluminescence in live individuals, means that the purpose of these photophores is poorly understood.^[3] The eyes, which are large and well developed, contain visual pigments indicative of maximum sensitivity in deep blue light (~480nm), as is common in mesopelagic fishes.^[4]

Trophic Ecology

Xenodermichthys copei is a predator that feeds on pelagic organisms, with a diet primarily composed of planktonic and micronektonic crustaceans, including natant decapod prawns, calanoid copepods, and both gammarid and hyperiid amphipods.^[5]^[6]^[7] X. copei also feeds on gelatinous zooplankton,^[6] including salps.^[8] However, on the Chatham Rise in New Zealand salps are fed upon by two other species of slickhead (Alepocephalus antipodianus and A. australis) and appear absent from the diet of X. copei; this appears to be an example of resource partitioning.^[5] Additionally, fragments of other fish, radiolarians^[6] and small cephalopods^[9] have been reported as parts of their diet. X. copei does not appear to forage on benthic organisms, regardless of whether the individual is caught in a pelagic or demersal setting.^[6]

A number of organisms prey upon Xenodermichthys copei, including the roundnose grenadier, Coryphaenoides rupestris, itself a benthopelagic predator.^[9] It is a very minor part of the diet of the black scabbardfish Aphanopus carbo,^[10] which is a generalist mesopelagic predator, and is present in the diet of the cut-throat eel Synaphobranchus kaupi.^[11] While it is also fed upon by cetaceans, including the striped dolphin Stenella coeruleoalba, it appears to be actively disregarded by common dolphins (Delphinus delphis) in the Bay of Biscay, which instead target high-energy food sources like the lanternfish Notoscopelus kroyerii.^[12]

Parasites

Xenodermichthys copei is host to a number of endoparasites, including trematodes (Paraccacladium jamiesoni,^[13] Steringophorus blackeri,^[14] Dinosoma ventrovesiculare^[15], and Helicometra sp.^[15]), and cestodes (Probothriocephalus alaini).^[16]

References

^ Hulley, P. (2015). "Xenodermichthys copei". IUCN Red List of Threatened Species. 2015: e.T15149335A15149338. doi:10.2305/IUCN.UK.2015-4.RLTS.T15149335A15149338.en. Retrieved 7 October 2024.
^ ^a ^b ^c Carvalho, F. P.; Almeida, A. J. (1988). "Notes on Xenodermichthys copei (Gill, 1884) (Pisces: Alepocephalidae)" (PDF). Cybium. 12 (2): 161–166.
^ ^a ^b Best, A. C. G.; Bone, Q. (1976). "On the integument and photophores of the alepocephalid fishes Xenodermichthys and Photostylus". Journal of the Marine Biological Association of the United Kingdom. 56 (1): 227–236. Bibcode:1976JMBUK..56..227B. doi:10.1017/S0025315400020567.
^ Partridge, JC; Archer, SN; Lythgoe, JN (1988). "Visual pigments in the individual rods of deep-sea fishes". Journal of Comparative Physiology A (162): 543–550.
^ ^a ^b Jones, M. R. L.; Breen, B. B. (2013-09-01). "Food and feeding relationships of three sympatric slickhead species (Pisces: Alepocephalidae) from northeastern Chatham Rise, New Zealand". Deep Sea Research Part I: Oceanographic Research Papers. 79: 1–9. Bibcode:2013DSRI...79....1J. doi:10.1016/j.dsr.2013.04.011. ISSN 0967-0637.
^ ^a ^b ^c ^d Mauchline, J; Gordon, JDM (1983). "Diets of clupeoid, stomiatoid and salmonoid fish of the Rockall Trough, northeastern Atlantic Ocean". Marine Biology. 77 (1): 67–78. Bibcode:1983MarBi..77...67M. doi:10.1007/BF00393211.
^ Roe, HSJ; Badcock, J (1984). "The Diel Migrations and Distributions within a Mesopelagic Community in the North East Atlantic. 5. Vertical Migrations and Feeding of Fish". Progress in Oceanography. 13 (3): 389–424. Bibcode:1984PrOce..13..389R. doi:10.1016/0079-6611(84)90014-4.
^ Kashkina, AA (1986). "Feeding of fishes on salps (Tunicata, Thaliacaea)". Journal of Ichthyology. 26 (3): 57–64.
^ ^a ^b Markle, DF (1986). Smith's Sea Fishes; Alepocephalidae. Springer-Verlag. pp. 218–223.
^ Santos, AR; Trueman, CN; Connolly, P; Rogan, E (2013). "Trophic ecology of black scabbardfish, Aphanopus carbo in the NE Atlantic—Assessment through stomach content and stable isotope analyses". Deep Sea Research Part 1: Oceanographic Research Papers. 77: 1–10. Bibcode:2013DSRI...77....1S. doi:10.1016/j.dsr.2013.02.009.
^ Gordon, JDM; Mauchline, J (1996). "The distribution and diet of the dominant, slope-dwelling eel, Synaphobranchus kaupi, of the Rockall Trough". Journal of the Marine Biological Association of the United Kingdom. 76 (2): 493–503. Bibcode:1996JMBUK..76..493G. doi:10.1017/S0025315400030691.
^ Spitz, Jérôme; Mourocq, Emeline; Leauté, Jean-Pierre; Quéro, Jean-Claude; Ridoux, Vincent (2010-07-31). "Prey selection by the common dolphin: Fulfilling high energy requirements with high quality food". Journal of Experimental Marine Biology and Ecology. 390 (2): 73–77. Bibcode:2010JEMBE.390...73S. doi:10.1016/j.jembe.2010.05.010. ISSN 0022-0981.
^ Gaevskaya, AV; Aleshkina, LD (1983). "New finds of fish trematodes on the Atlantic coast of Africa". Parazitologiya. 17 (1): 12–17.
^ Bray, RA (1973). "Some digenetic trematodes in fishes from the Bay of Biscay and nearby waters". Bulletin of the British Museum (Natural History), Zoology. 26 (2): 151–183.
^ ^a ^b Strona, Giovanni; Palomares, Maria Lourdes D.; Bailly, Nicolas; Galli, Paolo; Lafferty, Kevin D. (February 2013). "Host range, host ecology, and distribution of more than 11 800 fish parasite species: Ecological Archives E094‐045". Ecology. 94 (2): 544–544. doi:10.1890/12-1419.1. ISSN 0012-9658.
^ Scholz, Tomáš; Bray, Rodney A. (2001-11-01). "Probothriocephalus alaini n. sp. (Cestoda: Triaenophoridae) from the deep-sea fish Xenodermichthys copei in the North Atlantic Ocean". Systematic Parasitology. 50 (3): 231–235. doi:10.1023/A:1012214932377. ISSN 1573-5192.

"Xenodermichthys copei". Integrated Taxonomic Information System. Retrieved 18 April 2006.
Froese, Rainer; Pauly, Daniel (eds.). "Xenodermichthys copei". FishBase. February 2012 version.
Tony Ayling; Geoffrey Cox (1982). Collins Guide to the Sea Fishes of New Zealand. Auckland, New Zealand: William Collins Publishers Ltd. ISBN 978-0-00-216987-5.