The Japanese lanternfish, Notoscopelus japonicus (Tanaka, 1908), is for the first time recorded from Taiwan based on four specimens. This species has previously been known from temperate waters of the North and Central Pacific Ocean, therefore our specimens represent the southernmost record of this species. Fresh photographs and a detailed description are provided. Currently, 60 species in 17 genera of myctophids are known from Taiwanese waters, including three species representing Notoscopelus. A checklist of myctophids of Taiwan is provided and discussed.

Biodiversity, ichthyology, morphology, new record, photophores, taxonomy

The lanternfish genus Notoscopelus Günther, 1864 is a small group of fishes, with six species currently recognized as valid (Krefft and Bekker 1973; Nafpaktitis 1975; Fujii and Uyeno 1976; Paxton 1979). They are characterized by having: three or four precaudal photophores (Prc); procurrent caudal-fin rays stiff and spine like; caudal luminous glands absent or present only in adult males and forming a series of overlapping scale-like structures and not bordered by black pigments; second subpectoral photophore (PVO2) distinctly above level of pectoral-fin origin; postero-lateral photophores (Pol) two or three and arranged horizontally (Nafpaktitis 1975; Paxton and Hulley 1999).

One of the six species, Notoscopelus japonicus (Tanaka, 1908) was originally described based on a single specimen collected from Sagami Bay, Japan (Fujii and Uyeno 1976). It can be distinguished from congeners in having body covered by ctenoid scales (Nafpaktitis 1975), as well as other characters such as lateral-line scales 42–43, total vertebrae 40–42, Prc 2 + 2 = 4 (Fujii and Uyeno 1976). This species is widespread in the temperate waters of the North and Central Pacific Ocean, including Korea, Japan, Russia, Hawaii, and Alaska (Tanaka 1908; Peden and Hughes 1986; Sheiko and Fedorov 2000; Mundy 2005; Park et al. 2019).

The taxonomy of myctophid species in Taiwan was first reviewed by Mok (1993), who recognized five genera and 10 species. Subsequently, a comprehensive review by Wang and Chen (2001) recognized 40 species across 16 genera. Wang and Shao (2006) later expanded this list by adding ten new records. Shen and Wu (2011) reported 47 species in 17 genera, and no new records were reported. Kai and Nakabo included Taiwan as the distributional record of Ceratoscopelus townsendi (Eigenmann et Eigenmann, 1889) and Diaphus mollis Tåning, 1928 without reporting voucher specimens. Teramura (2019) documented 19 species and 9 genera from southwestern Taiwan, including Dasyscopelus orientalis Gilbert, 1913, Diaphus burtoni Fowler, 1934, and Diaphus nielseni Nafpaktitis, 1978 as new records, along with two potentially undescribed species of Lampanyctus Bonaparte, 1840. More recently, Ng et al. (2024a) reported Centrobranchus andreae (Lütken, 1892) and Dasyscopelus selenops (Tåning, 1928) from Taiwan. Ng et al. (2024b) reported 21 species and 9 genera from Dong-sha Island, though some specimens could not be identified to species level due to poor condition. Notably, two specimens of Diaphus adenomus Gilbert, 1905 represent the first record of this species from both Taiwan and the northwestern Pacific Ocean; and Diaphus perspicillatus (Ogilby, 1898), Diaphus problematicus Parr, 1928 are new records from Taiwan (Ng et al. 2024b). Currently, 59 species representing 17 genera of Myctophidae are known from Taiwan’s exclusive economic zone (EEZ).

Recently, four lanternfish specimens were collected from northeastern and southwestern Taiwan via commercial bottom trawling. After close examination, they are identified as N. japonicus based on the aforementioned characteristics. Our specimens represent the first record from Taiwan and the southernmost record in the northwestern Pacific Ocean. A detailed description of the specimens is provided and compared to other specimens.

Taxonomy and classification of genera follow Martin et al. (2018). Specimens were fixed in 4% formaldehyde and transferred to 70% ethanol for permanent preservation. The specimens were deposited at the Pisces Collection, National Museum of Marine Biology and Aquarium, Pingtung, Taiwan (NMMB-P) and the Laboratory of Aquatic Ecology, Department of Aquaculture, National Taiwan Ocean University (TOU-AE).

Counts follow Nafpaktitis and Nafpaktitis (1969) and Nafpaktitis (1975). Paired fins and lateral-line scales are presented as left/right whenever available. Vertebral counts were determined by X-ray filming in the National Taiwan Ocean University or a digital X-ray machine at NMMB. Terminology of photophores follow Nakabo (2002) and abbreviated as follows: Ant, antorbital organ; AOa, anterior anal organs; AOp, posterior anal organs; Cp, cheek photophores; Dn, dorsonasal organ; INGL, infracaudal luminous gland; Op, opercular organs; PLO, suprapectoral organ; PO, thoracic organs; Pol, posterolateral organ; Prc, precaudal organs; PVO, subpectoral organs; SAO, supraanal organs; So, suborbital organ; SUGL, supracaudal luminous gland; Suo, supraorbital organ; VLO, supraventral organ; Vn, ventronasal organ; VO, ventral organs.

Measurements generally follow Hubbs and Lagler (1958), with the following additions: preadipose length, measured from the anterior most margin of maxilla to adipose-fin origin; dorsal fin–adipose-fin length, distance between end of dorsal-fin base and adipose-fin origin; and adipose-fin length, base of adipose fin. Measurements were made with digital calipers and rounding to the nearest 0.1 mm. Morphometric data were presented as percentages of standard length (SL) and/or head length (HL), unless otherwise stated.

The presently reported specimens are identified as Notoscopelus japonicus based on the following characteristics: body scales ctenoid (as observed from remaining scales); lateral-line scales 42–44; Prc 2 + 2 = 4; and vertebrae 16–17 + 24–26 = 41–42 (Nafpaktitis 1975; Fujii and Uyeno 1976; Nakabo and Kai 2013). Compared to data of other specimens, several major differences were noted. Our specimens exhibit more pelvic-fin rays (9, vs. 8 in Nakagawa and Motomura 2020; Table 1), longer eye diameter (5.2%–6.2%SL, vs. 4.7%–5.1%SL; Table 2), longer interorbital width (6.2%–7.1%SL, vs. 5.3%–6.0%SL), longer pectoral fin (10.2%–10.5%SL, vs. 7.0%–7.9%SL). We suggest that more specimens are needed to determine if these differences are intraspecific variations or not. Other minor differences (e.g., slightly shorter body depth, prepelvic length, and caudal-peduncle length) are herein considered intraspecific variations.

Checklist of myctophids from Taiwan. Table 3 provides a total list of species recorded from Taiwan, and their revised Chinese names. The species recorded in the literature are somewhat inconsistent and confusing. For example: Diaphus taaningi Norman, 1930 recorded by Mok (1993) was not mentioned in the review by Wang and Chen (2001) but later recorded by Shen and Wu (2011); Di. mollis is currently only known from Nakabo and Kai (2013) and no voucher specimens are provided; and several species, such as Da. orientalis and Di. nielseni reported by Teramura (2019), and Di. perspicillatus and Di. problematicus reported by Ng et al. (2024b), are actually new records but not mentioned in the text.

With the addition of N. japonicus, a total of 60 myctophid species across 17 genera are currently recognized from Taiwanese waters. Of which, three species belong to the genus Notoscopelus: N. japonicus, Notoscopelus caudispinosus (Johnson, 1863), and N. resplendens (Richardson, 1845). Additionally, C. andreae, Da. orientalis, Da. selenops, Di. adenomus, Di. burtoni, Di. nielseni, Di. perspicillatus, Di. problematicus are reported recently (Teramura 2019; Ng et al. 2024a, b).

We thank H.-C. Ho (NKUST) for providing facilities and resource materials; K.-S. Wu (NSYSU) for collecting one of the specimens; Y.-C. Hsu (NSYSU) for taking photographs; and P.-N. Lee (NMMBA) for curatorial assistance. This study was supported by the National Science and Technology Council, Taiwan and National Penghu University of Science and Technology, Taiwan.