Eumecichthys

Unicorn crestfish
Eumecichthys fiski, conventional and X-ray images
Conservation status
Least Concern  (IUCN 3.1) [1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Order:	Lampriformes
Family:	Lophotidae
Genus:	Eumecichthys Regan, 1907
Species:	E. fiski
Binomial name
Eumecichthys fiski (Günther, 1890)
Synonyms
Lophotes fiskiGünther, 1890

Eumecichthys fiski, the unicorn crestfish or unicornfish, is a very rare, little-known species of crestfish in the family Lophotidae, and the only member of the genus Eumecichthys. It likely has a worldwide distribution, having been first discovered offshore of Kalk Bay, South Africa, and subsequently reported from the Sea of Japan, southwest Florida, Clarion Island off Mexico, Hawaii, and India. Reports from the Bering Sea are likely erroneous. It is found in the bathypelagic zone, at depths around 1,000 m (3,300 ft). ^{[2] [3]}

Description

This species has a highly elongate, ribbon-like body reaching up to 150 cm (59 in) in length. ^[2] Its common name derives from a horn-like supraoccipital process projecting forward above the eyes. ^[4] The upper jaw is protrusible, with small conical teeth adapted for seizing small fishes and pelagic invertebrates. ^[5] The dorsal fin extends the full length of the body with 310–392 soft rays, the first three to five rays forming an elongated pennant at the cranial ridge. The pectoral fins contain 13–15 rays, while pelvic fins are absent. The anal fin contains 5–9 rays and is split in adults to form two rows of nubbins. The caudal fin has 12–13 rays, the lowermost being enlarged and bony. Coloration is silvery with 24–60 dark subvertical bands; dorsal and caudal fins are crimson. ^[6]

Juveniles are smaller, with less developed cranial horns, fewer subvertical bands, and shorter dorsal-fin pennants, reflecting ontogenetic development. The flexible dorsal-fin pennants may be raised or lowered, potentially serving as a defensive mechanism. Compared with other lampriforms such as Lophotus lacepede and Zu cristatus, E. fiski is distinct in its horn, crimson fins, and unusually high dorsal-ray count. Its laterally compressed, ribbon-like body is adapted for efficient swimming in the bathypelagic zone. Like other lampriforms, it lacks a swim bladder, relying on lipid-rich tissues for buoyancy. ^[7]

Eumecichthys is one of three lampriform genera with ink tubes that expel black fluid from the cloaca as a defense. The ink tube, derived from a primitive gut, runs above the intestine. ^[3] Predators include the longnose lancetfish (Alepisaurus ferox), with specimens found that had ingested unicorn crestfish. ^[8] An extinct relative, Babelichthys , is known from the Eocene of Iran. ^[9]

Phylogenetic studies place Eumecichthys at the base of Lampriformes, suggesting early divergence in acanthomorph evolution. Fossil records, including Babelichthys, support long-term morphological conservation of dorsal-fin pennants and cranial horn. Molecular analyses show shared evolutionary history with other lampriforms, reflecting adaptive radiation in pelagic ecosystems. ^{[10] [11]}

Geographical distribution

Distribution map of the Lophotidae family occurrence in the Mediterranean Sea, 80 in this case, of the unique species reported in the basin, Lophotus lacepede.

Eumecichthys fiski is recorded worldwide in deep pelagic waters, including South Africa, the Sea of Japan, southwest Florida, Clarion Island, Hawaii, and India. Recent captures in the Canary upwelling zone indicate preference for nutrient-rich midwater habitats where vertical migrations of prey occur. ^[12] The species is naturally rare, mostly collected as bycatch, indicating low population density despite broad geographic range.

Ecology and life history

Little is known about reproduction; it is presumed to be a pelagic spawner, releasing eggs into open water. Juveniles are paler, with shorter dorsal-fin pennants and smaller cranial horns. Growth rates, lifespan, and age at maturity remain unknown but likely moderate to long, as in other deep-sea pelagic fishes. ^{[7] [3]}

E. fiski is carnivorous, feeding on small fishes and pelagic invertebrates. Diel vertical migrations likely move individuals from bathypelagic to mesopelagic zones to feed while avoiding predators. Observed stomach contents show diverse mesopelagic fish, cephalopods, and crustaceans. Juveniles likely follow similar feeding behavior. The ink tube provides a unique defense against predators in low-light pelagic conditions. ^{[3] [13]}

Conservation

The IUCN classifies Eumecichthys fiski as Least Concern due to wide but sparse distribution and lack of targeted fisheries. ^[1] Threats are mainly indirect: climate-driven changes in deep-water temperature and oxygen, shifts in prey availability, and deep-sea trawling. Fossil evidence suggests the lineage has persisted tens of millions of years, indicating resilience. Continued research is needed on ecological roles, population trends, and vulnerability to anthropogenic impacts. ^[14]

Unicorn crestfish

References

1. Knudsen, S. (2015). Eumecichthys fiski. The IUCN Red List of Threatened Species doi:10.2305/IUCN.UK.2015-4.RLTS.T190107A60791470.en
2. Froese, Rainer; Pauly, Daniel (eds.). "Eumecichthys fiski". FishBase . March 2009 version.
3. Honma, Yoshiharu; Ushiki, Tatsuo; Takeda, Masaei (Feb 1999). "Histology of the ink tube and its associated organs in a unicornfish, Eumecichthys fiskii (Lampridiformes)". Ichthyological Research. 46 (1): 19–25. Bibcode:1999IchtR..46...19H. doi:10.1007/BF02674944. S2CID   25284408.
4. Richards, W.J. (2006). Early stages of Atlantic fishes: an identification guide for the western central North Atlantic. CRC Press. ISBN   978-0-8493-1916-7.
5. Olney, J.E. (1998). "Lophotidae". In Carpenter, K.E.; Niem, V.H. (eds.). FAO species identification guide for fishery purposes. The living marine resources of the Western Central Pacific. Food and Agricultural Organization of the United Nations. ISBN   92-5-104302-7.
6. Smith, J.L.B.; Smith, M.M.; Heemstra, P. (2003). Smiths' Sea Fishes. Struik. ISBN   1-86872-890-0.
7. Albano, Marco; D’Iglio, Claudio; Spanò, Nunziacarla; De Oliveira Fernandes, Jorge Manuel; Savoca, Serena; Capillo, Gioele (2022). "Distribution of the order Lampriformes in the Mediterranean Sea with notes on their biology, morphology, and taxonomy". Biology. 11 (10): 1534. doi: 10.3390/biology11101534 . PMID   36290437.
8. Fujita, K. & Hattori, J. (1976). "Stomach Content Analysis of Longnose Lancetfish, Alepisaurus ferox in the Eastern Indian Ocean and the Coral Sea". Japanese Journal of Ichthyology. 23 (3): 133–142. doi:10.11369/jji1950.23.133. S2CID   89359106.
9. Davesne, Donald (2017-06-28). "A fossil unicorn crestfish (Teleostei, Lampridiformes, Lophotidae) from the Eocene of Iran". PeerJ. 5 e3381. doi: 10.7717/peerj.3381 . PMC   5493034 . PMID   28674642.
10. Wang, Jin-fang (2023). "Phylogenetic and evolutionary comparison of mitogenomes reveal adaptive radiation of lampriform fishes". International Journal of Molecular Sciences. 24 (10): 8756. doi: 10.3390/ijms24108756 . PMID   37240101.
11. Brownstein, Chase D. (2024). "Evolutionary origins of the lampriform pelagic radiation". Zoological Journal of the Linnean Society. 201 (2): 422–430. doi:10.1093/zoolinnean/zlad142.
12. Kukuev, E. I. (2020). "First capture of unicorn crestfish Eumecichthys fiski (Lophotidae) in the Canary upwelling zone". Journal of Ichthyology. 60 (5): 791–796. doi:10.1134/S0032945220040098.
13. Falsone, Fabio (2017). "Occurrence of two rare species from order Lampriformes in northern Sicily, Italy". Acta Adriatica. 58 (1): 137–146. doi:10.32582/aa.58.1.11.
14. Brownstein, Chase D. (2024). "Evolutionary origins of the lampriform pelagic radiation". Zoological Journal of the Linnean Society. 201 (2): 422–430. doi:10.1093/zoolinnean/zlad142.