Lanternfish are small, silvery denizens of the ocean’s twilight zone, named for the rows of light-producing photophores that stud their bodies. They are among the most abundant vertebrates on Earth, forming a critical link in the marine food web between the plankton they graze and the larger predators that hunt them at night. The genus Notoscopelus is a compact branch of this family, with only six species currently recognized as valid. Members of the group are distinguished by three or four precaudal photophores, stiff and spine-like procurrent caudal-fin rays, and a distinctive arrangement of light organs, including a second subpectoral photophore positioned distinctly above the level of the pectoral-fin origin.

Notoscopelus japonicus was originally described in 1908 from a single specimen collected in Sagami Bay, Japan. It can be separated from its close relatives by a combination of anatomical features: the body is covered in ctenoid scales, the lateral line carries 42 to 43 scales, the vertebral count totals 40 to 42, and the precaudal photophores are arranged in a two-plus-two pattern. Until this study, the species was known from temperate waters across a vast arc of the Pacific, including Russia’s Kamchatka Peninsula, Korea, the Japanese archipelago, the Hawaiian seamounts, the west coast of Canada, and Alaska. A mesopelagic species, it spends daylight hours below 300 meters and migrates upward to depths of 20 to 200 meters at night.

The four Taiwanese specimens were collected over a span of months from two geographically separate fishing grounds. One male, measuring 126.5 millimeters in standard length, came from off Dong-gang fishing port in Pingtung, southwestern Taiwan, in November 2024. The other three were taken by commercial trawler off Daxi fishing port in Yilan, northeastern Taiwan, in February and March of 2023 and 2024, ranging from 122.1 to 134.2 millimeters in standard length. Two of the specimens are males, one could not be sexed, and all were fixed in formaldehyde and preserved in ethanol for permanent curation at Taiwanese institutional collections.

Identifying lanternfish to species level is exacting work, because the family is defined largely by subtle differences in photophore placement, fin-ray counts, and scale characters. The researchers confirmed the identification through a detailed morphological examination supported by X-ray imaging. The Taiwanese specimens showed dorsal-fin rays of 20 to 21, pectoral-fin rays of 11, pelvic-fin rays of 9, anal-fin rays of 18 to 20, and gill rakers on the first arch totaling 23 to 26. Lateral-line scale counts of 42 to 44 and vertebral counts of 41 to 42 fell squarely within the published range for the species, as did the characteristic four precaudal photophores arranged in two pairs.

The photophore architecture matched the species diagnosis in every detail. The anterior anal organs numbered 8 to 10, the posterior anal organs 6 to 7, and the supraanal organs comprised three photophores all positioned ahead of the anal-fin origin. The dorsonasal organ was well developed and crescent-shaped, sitting at the ten o’clock position relative to the eye, while the smaller ventronasal organ sat at eight o’clock. In the males, both the infracaudal and supracaudal luminous glands were present but obscure, lacking the sharply defined borders seen in some related species. Fresh specimens displayed a pale body with scale pockets outlined in black, a uniformly black head, and dusky fin rays with a darker caudal base.

Not every measurement lined up perfectly with the historical descriptions, and the authors are candid about the discrepancies. The Taiwanese fish carry nine pelvic-fin rays rather than the eight reported in a recent Japanese study, along with proportionally longer eye diameters, wider interorbital spaces, and notably longer pectoral fins than their northern counterparts. The researchers suggest that additional specimens will be needed to determine whether these differences represent intraspecific geographic variation or something more significant. Minor deviations in body depth, prepelvic length, and caudal-peduncle proportions were judged to fall within normal variation for the species.

Beyond the range extension itself, the paper delivers a comprehensive checklist of Taiwan’s myctophid fauna, a tally that has grown considerably over three decades of incremental documentation. The first review in 1993 recognized just five genera and ten species; a 2001 synthesis raised that to 40 species across 16 genera, and subsequent additions have steadily expanded the list. With N. japonicus now included, 60 species in 17 genera are recognized from Taiwanese waters, three of them belonging to the genus Notoscopelus. The authors also flag inconsistencies in the historical record, including species reported without voucher specimens and several recent records that were new to Taiwan but never explicitly identified as such in the original publications.

Why a temperate lanternfish should appear in subtropical trawl nets is a question the record alone cannot answer. Deep-water mesopelagic species can be carried far from their usual haunts by currents, upwelling events, or the shifting thermal structure of the water column, and bottom trawlers sampling slopes and canyons routinely intercept animals that spend their days hundreds of meters down. Whatever the mechanism, the finding underscores how incompletely the twilight zone is surveyed even in heavily fished regions. Each new record refines the biogeographic map of a family that may account for a substantial share of the ocean’s total fish biomass, and the authors’ careful documentation, complete with fresh photographs, meristic tables, and museum-vouchered specimens, ensures that this southernmost outpost of the Japanese lanternfish can be verified and built upon by future surveys of the northwestern Pacific’s deep-pelagic fauna.

Subject of Research: First record and southernmost range extension of the Japanese lanternfish Notoscopelus japonicus in Taiwan

Article Title: A southward range extension of the Japanese lanternfish, Notoscopelus japonicus ( Actinopterygii , Myctophiformes , Myctophidae ), from Taiwan, northwestern Pacific Ocean, with a checklist of myctophids from Taiwan

Article References: Su, Y., Huang, J.-F., & Yang, F.-Y. (2025). A southward range extension of the Japanese lanternfish, Notoscopelus japonicus (Actinopterygii, Myctophiformes, Myctophidae), from Taiwan, northwestern Pacific Ocean, with a checklist of myctophids from Taiwan. Acta Ichthyologica et Piscatoria, 55, 123-131. https://doi.org/10.3897/aiep.55.151025

Image Credits: AI Generated

DOI: 10.3897/aiep.55.151025

Keywords: lanternfish, Notoscopelus japonicus, Myctophidae, Taiwan, range extension, deep-sea fish, mesopelagic, biogeography, taxonomy, new record, northwestern Pacific, ichthyology