Taxonomic study records large-eyed sackfish 1,200 km south in western Taiwan

A taxonomic study based on a single fish specimen reports a new western Taiwan record of the large-eyed sackfish Neoepinnula minetomai , extending its documented range about 1,200 km southward from southern Japan. The 322 mm standard-length fish was identified as N. minetomai through its body proportions, large eye, teeth, lateral-line morphology and other diagnostic characters. The study also provides previously unreported details about its lateral-line scales and otoliths.

A local fisherman had caught it and sold it as food, and the researchers bought it immediately after it had been gutted before sending it to the National Museum of Marine Biology and Aquarium in Pingtung for examination. Its standard length was 322 mm, compared with 327 mm for the holotype and 286 mm for the paratype. Counts and measurements followed the procedures used by Nakayama, Kimura and Endo in the 2014 description of N. minetomai , which generally followed Hubbs and Lagler.

The number of vertebrae was counted from a digital film of the museum specimen. The fish had 16 precaudal and 16 caudal vertebrae, for a total of 32. Its dorsal fin had 16 spines, one isolated spine and 20 soft rays; the pectoral fin had 15 rays, the pelvic fin one spine and five rays, and the anal fin three spines and 20 rays.

The deeply forked caudal fin had nine principal rays in each lobe. The body was relatively short, deep and moderately compressed, reaching its greatest depth at the pelvic-fin origin. Its body depth was 3.5 in standard length, meaning that standard length was 3.5 times the measured depth.

The head was large, with standard length 3.2 times head length. The orbit was large and circular, with a fleshy diameter of 3.4 in head length, so head length was 3.4 times the fleshy orbital diameter. These proportional measurements were consistent with the species’ compact form and conspicuous eye.

Dental and fin characteristics supported the identification. Three large fixed fangs occurred at the front of the roof of the oral cavity, accompanied by two small backward-depressed teeth. The premaxilla carried a single row of approximately 27 laterally compressed, slightly recurved teeth, with the middle teeth largest.

About 11 larger teeth occurred in the dentary, increasing in height toward the rear. The short, deep body, large eye and absence of enlarged canine teeth on the lower jaw were identified as readily recognizable features of N. minetomai . The lateral line formed a single canal extending along the dorsal profile, chiefly near the dorsal-fin base, and continued along the posterior margin of the head, pectoral-fin base, lower margin of the belly and anal-fin base before passing through the caudal peduncle.

The researchers counted 103 lateral-line scales in the upper horizontal portion, 39 in the anterior vertical portion and 111 in the lower horizontal portion. These scales were larger than neighboring body scales and had short canal openings that opened in different directions according to their position. The paired sagittal otoliths measured 10.12 mm and 10.21 mm in length.

Both were elliptical, with a pointed anterior rim, a deep notch and a large pointed rostrum, while the antirostrum was truncated and very short. Their length-to-height ratios were 1.72 and 1.77. The centrally positioned sulcus had an ostium deeper than the cauda, although the two regions were only slightly differentiated.

Crenulated or lobed margins and small fenestrations in the ventral area were also recorded. The authors added the scale arrangement and otolith morphology to the available diagnostic information for the species. When fresh, the specimen was generally silvery gray, with a slightly darker dorsum and gill cover.

Its fins were dusky, and the first dorsal fin had a black margin. Comparison with the type series showed a slightly smaller head in the Taiwanese fish, at 31.2% of standard length versus 33.4–34.8% in the holotype and paratype, and a slightly smaller eye, at 9.2% versus 10.6–10.9% of standard length. The researchers treated these differences as individual variation.

The record brings the number of gempylid species documented in Taiwan to 12, based on the study’s accompanying checklist. Its broader distributional significance remains uncertain because only the two Japanese type specimens and the Taiwanese fish are known. The authors suggested that N. minetomai may be very rare relative to its congeners and that its occurrence near small islands may indicate an insular association in the western Pacific.

However, the three known records do not establish population size, abundance or a distribution across the wider region, and the new Taiwan record is based on one market specimen.

Subject of Research: Taxonomic range record of Neoepinnula minetomai from western Taiwan based on one museum specimen

Article Title: New record of the large-eyed sackfish, Neoepinnula minetomai ( Actinopterygii , Scombriformes , Gempylidae ), from western Taiwan

Article References: Ho, H.-C., Cheng, Y.-N., Su, Y., Hsu, Y.-C., & Shyu, J.-F. (2025). New record of the large-eyed sackfish, Neoepinnula minetomai (Actinopterygii, Scombriformes, Gempylidae), from western Taiwan. Acta Ichthyologica et Piscatoria, 55, 341-347. https://doi.org/10.3897/aiep.55.172991

Image Credits: AI Generated

DOI: 10.3897/aiep.55.172991

Keywords: Neoepinnula minetomai, large-eyed sackfish, Gempylidae, Taiwan, taxonomic record, range extension, fish morphology, lateral-line scales, otolith morphology, Penghu Islands, record, large-eyed