Museum drawers yield a first for Taiwan: Hasselt’s rainbow sardine confirmed far north of its known Pacific range

Three slender fish, catalogued decades apart in the collection of the National Museum of Marine Biology and Aquarium in Taiwan, have turned out to be something no one had formally documented before: the first specimen-based records of Hasselt’s rainbow sardine, Dussumieria hasseltii, from Taiwanese waters. The specimens, collected from fishing ports in Pingtung and Kaohsiung in southwestern Taiwan, also mark the northernmost record of the species anywhere in the western Pacific Ocean, extending its confirmed range well beyond the Philippines where it had never previously been recorded north of Luzon.

The discovery, published in the journal Acta Ichthyologica et Piscatoria, matters far beyond a simple range extension. The genus Dussumieria, a group of small pelagic herrings known as rainbow sardines distributed widely across the Indo-west Pacific, has been in a state of taxonomic flux for decades. When the genus was first reviewed in 1963, it was treated as monospecific, with all specimens assigned to a single valid species, Dussumieria acuta. Later assessments recognized two species, D. acuta and D. elopsoides. But recent research has revealed that several distinct taxa were hidden within specimens previously identified under those broad names, and the genus now comprises nine valid species, including D. hasseltii, D. modakandai, D. productissima, and three species described only recently from the eastern coast of Africa, Fiji, and Australia.

That taxonomic churn explains why records of Dussumieria species from Taiwanese waters have long been ambiguous. Much of the published work on regional ichthyofaunas, including Taiwan’s, was last undertaken decades ago and relied on the classifications accepted at the time. Mid-twentieth-century authors did include Taiwan in the distributional range of D. hasseltii, but their reported counts of scale rows in longitudinal series, spanning 52 to 58, overlap with the counts of D. acuta, D. hasseltii, and D. modakandai alike, meaning those specimens could represent individuals of different species. One author even concluded that D. hasseltii was a synonym of D. elopsoides, making the basis of the identification extremely vague. Later accounts of D. elopsoides in Taiwan were too brief to determine which species had actually been collected, and a color photograph of an individual from the Penghu Islands was published without any morphological description at all.

The newly recognized specimens were collected at the Dong-gang fishing port in Pingtung in December 2003 and at the Ke-tzu-liao fishing port in Kaohsiung in March 2017. Two of the three fish measure 143.4 and 144.5 millimeters in standard length, while the Dong-gang specimen measures 138.6 millimeters. All three sat catalogued in the museum’s fish collection until the recent re-examination revealed their true identity, underscoring how voucher specimens preserved in institutional collections can settle questions that field notes and photographs cannot.

Identifying the specimens required careful attention to characters that earlier generations of researchers had overlooked. The Taiwanese fish are assignable to Dussumieria based on established diagnostic features, including 14 to 16 branchiostegal rays, rectangular premaxillae, 15 or 16 total anal-fin rays, a pointed isthmus, pelvic fins originating just below the dorsal-fin base, and the absence of keeled scutes on the abdomen. Within the genus, D. hasseltii can be distinguished from all congeners except D. elopsoides by having broad teeth bands on the palatine and pterygoid bones, where other species bear only a few sparsely distributed conical teeth. The critical separation from D. elopsoides lies in the pre-dorsal-fin length, which ranges from 57.5 to 60.6 percent of standard length in D. hasseltii but only 54.6 to 55.9 percent in D. elopsoides.

The Taiwanese specimens closely matched the diagnostic profile of D. hasseltii in every essential respect. Their bodies are slender, with depth less than 22 percent of standard length; the pre-dorsal-fin length exceeds 58 percent of standard length; the teeth on the palatine and pterygoid are dense, forming broad bands; no teeth are present on the parasphenoid; the longitudinal scale rows are numerous, at 57 to 59; and the total gill rakers on the first gill arch are few, below 39. The only deviation was a slightly higher count of pectoral-fin rays bearing melanophores, the dark pigment cells scattered along the fin rays that give the fish their characteristic coloration in preservation.

Detailed counts and measurements, taken with digital calipers to the nearest 0.1 millimeter and expressed as percentages of standard length or head length, generally aligned with those of reference specimens from across the Indo-west Pacific. The meristic characters of the Taiwanese fish, including dorsal-fin rays totaling 19 to 21, anal-fin rays totaling 15 to 16, and gill rakers on the first gill arch totaling 36 to 38, fell squarely within the ranges observed in 49 comparative specimens spanning from the Persian Gulf to Southeast Asia and the Philippines. The preserved coloration, with a uniformly pale brown lateral surface, a dark brown dorsum, pale yellow fins, and melanophores scattered on the eighth to fourteenth pectoral-fin rays from the uppermost, matched the species’ known appearance.

The recognition of D. hasseltii as a valid species is itself a recent development. Although Bleeker described the species in 1851, it had long been regarded as a junior synonym of D. acuta or D. elopsoides following the assessments of 1963 and 1985. Only in 2022 was it revalidated as a distinct species based on both diagnostic morphological features and divergence in COI barcode sequences, with its distributional range then understood to span the Indo-west Pacific from the Persian Gulf to the Philippines and Indonesia west of Lombok. A specimen subsequently reported from the Gulf of Papua in Papua New Guinea extended the range further, but no record had placed the species north of Luzon in the Pacific until now.

How did a sardine whose confirmed Pacific records stop at the Philippines turn up in Taiwanese waters? The authors point to oceanography. The main Kuroshio Current and a branch flow northward from Luzon to the east and west sides of Taiwan, respectively, and the Taiwanese specimens could have been transported by these currents from the Philippines. A similar pattern is known for Sardinella hualiensis, a dorosomatid fish belonging to the same order, Clupeiformes, which migrates between the Philippines and Taiwan. The finding suggests that the pelagic fish fauna of southern Taiwan is at least partially shared with that of the Philippine Islands, where D. hasseltii has been recorded from Luzon, Panay, Palawan, and Jolo, indicating the species may be commonly distributed throughout the archipelago.

There is also a conspicuous gap in the species’ mapped range along the continental coast. Although D. hasseltii has been recorded from the Gulf of Thailand, it has never been reported from the coastal areas of Vietnam or China, leaving a stretch of shoreline between its Thai and Taiwanese records where the species has not yet been documented. Whether that gap reflects genuine absence or simply a lack of recent survey work based on the latest classification remains unclear. The authors suggest that additional dussumierid species distributed in the Philippines, such as Dussumieria albulina, may also occur in Taiwanese waters through the same oceanographic connections. With three species of Dussumieria now confirmed from Taiwan, D. acuta, D. modakandai, and D. hasseltii, the island’s rainbow sardine fauna is only beginning to be understood, and museum collections in the region may hold further surprises for anyone willing to look closely at the fine details of teeth, scales, and pigment.

Subject of Research: First specimen-based Taiwanese records of the rainbow sardine Dussumieria hasseltii from Pingtung

Article Title: First specimen-based Taiwanese records of Dussumieria hasseltii ( Actinopterygii , Clupeiformes , Dussumieriidae ) from Pingtung

Article References: Hata, H., Sallan, L., & Ho, H.-C. (2025). First specimen-based Taiwanese records of Dussumieria hasseltii (Actinopterygii, Clupeiformes, Dussumieriidae) from Pingtung. Acta Ichthyologica et Piscatoria, 55, 167-173. https://doi.org/10.3897/aiep.55.156276

Image Credits: AI Generated

DOI: 10.3897/aiep.55.156276

Keywords: Dussumieria hasseltii, rainbow sardine, Taiwan, Pingtung, Dussumieriidae, Clupeiformes, taxonomy, voucher specimens, Kuroshio Current, Indo-west Pacific, First, specimen-based