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| Narcetes shonanmaruae Poulsen, Ida, Kawato & Fujiwara in Fujiwara, Kawato, Poulsen, ... et Tsuchida, 2021. |
Abstract
A novel species of the family Alepocephalidae (slickheads), Narcetes shonanmaruae, is described based on four specimens collected at depths greater than 2171 m in Suruga Bay, Japan. Compared to other alepocephalids, this species is colossal (reaching ca. 140 cm in total length and 25 kg in body weight) and possesses a unique combination of morphological characters comprising anal fin entirely behind the dorsal fin, multiserial teeth on jaws, more scale rows than congeners, precaudal vertebrae less than 30, seven branchiostegal rays, two epurals, and head smaller than those of relatives. Mitogenomic analyses also support the novelty of this large deep-sea slickhead. Although most slickheads are benthopelagic or mesopelagic feeders of gelatinous zooplankton, behavioural observations and dietary analyses indicate that the new species is piscivorous. In addition, a stable nitrogen isotope analysis of specific amino acids showed that N. shonanmaruae occupies one of the highest trophic positions reported from marine environments to date. Video footage recorded using a baited camera deployed at a depth of 2572 m in Suruga Bay revealed the active swimming behaviour of this slickhead. The scavenging ability and broad gape of N. shonanmaruae might be correlated with its colossal body size and relatively high trophic position.
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| Figure 2: Narcetes shonanmaruae. (a), (b), (d), (e) holotype (SH8-69). (c) paratype 3 (SH12-14). (f) paratype 2 (SH12-1). (a) Lateral view. (b) Computed tomography image of the endoskeleton. (c) Lateral view. Scale rows indicated. Lateral line scales not shown. (d) Lateral view of head. (e) Tooth pattern of upper jaw. mx: maxillary, pal: platine, pmx:premaxillary, vom: vomer. (f) Gill raker. Right side of first arch. (g) In situ video grab of active swimming individual recorded using a baited camera. |
Systematics
Family Alepocephalidae Bonaparte, 1846.
Genus Narcetes Alcock, 1890.
Narcetes shonanmaruae sp. nov. Poulsen, Ida, Kawato & Fujiwara
(proposed English name: Yokozuna Slickhead,
proposed Japanese name: Yokozuna Iwashi).
Species diagnosis: Anal fin entirely behind the dorsal fin. Teeth on premaxillary, maxillary, and dentary multiserial. Predorsal scale rows greater than 70. Longitudinal scale rows greater than 110. Dorsal to lateral line scale row greater than 15. Anal to lateral line scale rows greater than 17. Branchiostegal rays 7. Dorsal-fin rays less than 15. Precaudal vertebrae less than 30. Epurals 2. Lengths of head, snout, upper and lower jaws, orbit diameter, dorsal and anal fin bases relatively short against standard length (SL).
Remarks: Narcetes shonanmaruae sp. nov. is similar to N. erimelas in anal fin position being entirely behind the dorsal fin. However, our species differs from all the other Narcetes species based on the following morphological characters: length of dorsal fin base less than 13% SL; upper jaw length less than 14% SL; lower jaw length less than 15% SL; number of dorsal-fin rays less than 15; number of predorsal scale rows greater than 70; number of dorsal to lateral line scale rows greater than 16; number of anal to lateral line scale rows greater than 17.
Etymology: The species epithet shonanmaruae is a feminine noun in Latin, referring to the ship ‘Shonan maru’ from which the type materials were caught, honouring the vessel’s considerable contribution to deep-sea fish research in the area. The proposed Japanese vernacular name is ‘Yokozuna Iwashi’. This species belongs to the family Alepocephalidae, which is referred to as ‘Sekitori Iwashi’ in Japanese: ‘Sekitori’ meaning a sumo wrestler and ‘Iwashi’ meaning a sardine, thereby implying a massive sardine. The term ‘Yokozuna’ refers to the highest rank in sumo wrestling in Japan. Accordingly, we propose the name ‘Yokozuna Iwashi’ as being indicative of the large body size and the high trophic position of the newly described species. English vernacular name: Yokozuna Slickhead.
Distribution: Currently only known from Suruga Bay at depths deeper than 2100 m.
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| Figure 1: Research area and location of each longline and baited camera deployment. This map was created using QGIS software version 2.14.10 (https://qgis.org/) and bathymetric data M7001 supplied by the Japan Hydrographic Association (https://www.jha.or.jp/en/jha/). Solid line: longline tracks of SH8 and SH12; S and E represent the start and end locations of longlines, respectively. Solid star: deployment location of baited camera (AT2-04). This map is under copyright © 2018 Yoshihiro Fujiwara. |
Yoshihiro Fujiwara, Masaru Kawato, Jan Yde Poulsen, Hitoshi Ida, Yoshito Chikaraishi, Naohiko Ohkouchi, Kazumasa Oguri, Shinpei Gotoh, Genki Ozawa, Sho Tanaka, Masaki Miya, Tetsuya Sado, Katsunori Kimoto, Takashi Toyofuku and Shinji Tsuchida. 2021. Discovery of A Colossal Slickhead (Alepocephaliformes: Alepocephalidae): An Active-swimming Top Predator in the Deep Waters of Suruga Bay, Japan. Scientific Reports. 11, 2490. DOI: 10.1038/s41598-020-80203-6
