Discovery of a colossal slickhead (Alepocephaliformes: Alepocephalidae): an active-swimming top predator in the deep waters of Suruga Bay, Japan

Yoshihiro Fujiwara,Genki Ozawa,Masaki Miya,Kazumasa Oguri,Naohiko Ohkouchi,Yoshito Chikaraishi,Shinpei Gotoh,Jan Yde Poulsen,Hitoshi Ida,Masaru Kawato,Katsunori Kimoto,Tetsuya Sado,Takashi Toyofuku,Sho Tanaka,Shinji Tsuchida

doi:10.1038/s41598-020-80203-6

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.

Highlights

A novel species of the family Alepocephalidae, Narcetes shonanmaruae, is described based on four specimens collected at depths greater than 2171 m in Suruga Bay, Japan
Four individuals of an alepocephalid species were collected from Suruga Bay using a bottom longline installed on the training vessel Shonan maru (SH) belonging to the Kanagawa Prefectural Marine Science High School
The first two individuals were collected at depths of 2171 m and 2179 m on 4th February 2016 during the cruise SH16-01, and the other two specimens were captured at depths of 2572 m and 2551 m on 23rd November 2016 during the cruise SH16-02 (Fig. 1, Table 1)

Summary

Introduction

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. Marine environments are increasingly being affected by global climate change and anthropogenic activities, leading to oceanic warming, acidification, and deoxygenation even in deep-sea r egions[1] Such global changes are assumed to initially affect large, predatory consumers and subsequently have repercussions for organisms at lower trophic levels[2]. The genus Narcetes Alcock, 1890, is a member of the family Alepocephalidae (slickheads), consisting of three named species, i.e., N. erimelas, N. lloydi, and N. stomias[10]. The members of this genus are bathypelagic, inhabiting depths between 700 and 2600 m, and are distributed globally. The members have 26–33 precaudal vertebrae and 18–25 caudal vertebrae (48–56 in total), with 3–14 more precaudal than caudal vertebrae, relatively large centra spaces for the spinal cord, 8–14 long pyloric caeca, generally 8 branchiostegal rays, and 3–6 + 1 + 10–17 gill rakers on the first a rch11. Sazonov[10] reviewed all species of the genus and synonymized Bathytroctes alveatus Garman, 1899 with N. erimelas Alcock, 1890 and N. kamoharai Okamura, 1984 and N. wonderi Herre, 1935 with Narcetes lloydi Fowler, 1934

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