Holotype.—MZB 28041, 46.7 mm SL (male), Lariang River near Lengkeka Village, Bada Valley, District Lore Barat, Poso Regency, Sulawesi Tengah, 01°52′38.05″S, 120°12′8.83″E, 752 m MSL, J. Möhring, F. K. Lakiu, and M. Mejía Estrada, 15 August 2023 (Figs. 1A, 2).

Paratypes.—MZB 28042–28048, 32.7–46.2 mm SL (4 males, 3 females), same metadata as holotype, except collected 14–15 August 2023; MZB 28049–28052, 34.8–39.5 mm SL (4 females), Malei River at Gintu Village, Bada Valley, District Lore Selatan, Poso Regency, Sulawesi Tengah, 01°53′13.95″S, 120°14′6.25″E, 760 m MSL, F. Herder and D. F. Mokodongan, 21 September 2023; ZFMK ICH-136000–136007, 35.3–52.5 mm SL (5 males, 3 females), same metadata as holotype, except collected 14–15 August 2023.

Non-type material.—MZB 28053–28054, 38.7–44.4 mm SL (2 males), Lariang River, Watutau Village, Napu Valley, District Lore Peore, Poso Regency, Sulawesi Tengah, 01°33′34.53″S, 120°20′16.96″E, 1,084 m MSL, J. Möhring, A. Gani, Z. Jusman, and D. F. Mokodongan, 30 September 2023; MZB 28055–28069, 35.8–45.3 mm SL (4 males, 11 females), Pembangu River, Watutau Village, Napu Valley, District Lore Peore, Poso Regency, Sulawesi Tengah, 01°33′51.41″S, 120°20′33.00″E, 1,085 m MSL, J. Möhring, A. Gani, Z. Jusman, and D. F. Mokodongan, 30 September 2023; ZFMK ICH-136008–136022, 37.7–49.3 mm SL (8 males, 7 females), same metadata as holotype, except collected 14 August 2023, pres. 96% ethanol; ZFMK ICH-136023, 39.3 mm SL, male, Lariang River, Watutau Village, Napu Valley, District Lore Peore, Poso Regency, Sulawesi Tengah, 01°33′34.53″S, 120°20′16.96″E, 1,084 m MSL, J. Möhring, A. Gani, Z. Jusman, and D. F. Mokodongan, 30 September 2023; ZFMK ICH-136024–136039, 32.2–47.1 mm SL (4 males, 12 females), Pembangu River, Watutau Village, Napu Valley, District Lore Peore, Poso Regency, Sulawesi Tengah, 01°33′51.41″S, 120°20′33.00″E, 1,085 m MSL, J. Möhring, A. Gani, Z. Jusman, and D. F. Mokodongan, 30 September 2023.

Diagnosis.—Oryzias polylepis is distinguished from all other known species of Oryzias, as well as all species of Adrianichthys except A. poptae, by its high number of scales in the lateral series (79–93 vs. <75; Parenti, 2008). It differs from A. poptae by its substantially smaller adult standard length (52 mm vs. 190 mm SL) and in having a substantially shorter snout (6.8–9.3 vs. 13.0–17.0) with superior and small mouth, vs. elongated snout with large terminal mouth in A. poptae.

Among the Sulawesi-endemic ricefish species, O. polylepis is further distinguished from O. asinua, O. celebensis, O. dopingdopingensis, O. hadiatyae, O. landangiensis, O. matanensis, O. soerotoi, O. wolasi, and O. woworae by the number of dorsal-fin rays (11–13 vs. <11; Parenti, 2008; Herder and Chapuis, 2010; Parenti and Hadiaty, 2010; Parenti et al., 2013; Mokodongan et al., 2014; Mandagi et al., 2018; Utama et al., 2022). From O. eversi, it differs in the number of anal-fin rays (19–23 vs. 17–18; Herder et al., 2012) and pectoral-fin rays (11–14 vs. 10). It is distinguished from geographically close endemic pelvic-brooding species of Lake Lindu, O. bonneorum and O. sarasinorum, by having fewer principal caudal-fin rays (i,4/5,i vs. i,5/6,i; Parenti, 2008) and a shorter head (23.1–26.4 vs. 29.0–32.0). It differs from sympatric O. kalimpaaensis by having a shorter head (23.1–26.4 vs. 30.6–33.2; Gani et al., 2022) and larger eyes relative to head length (32.6–40.7 vs. 26.3–29.6). Lacustrine species occurring in Lakes Mahalona, Lantoa, and Towuti, O. loxolepis, O. marmoratus, and O. profundicola, possess deeper bodies (15.2–21.4 vs. 24.8–35.2; Parenti, 2008; Kobayashi et al., 2023) and a truncate or round instead of lunate caudal-fin edge (Figs. 1–4). The Oryzias endemic to Lake Poso, O. nebulosus, O. nigrimas, and O. orthognathus, all differ from O. polylepis by their greater predorsal length (67.2–70.6 vs. 73.0–79.8; Parenti, 2008).

Oryzias polylepis differs in life coloration from all other Oryzias, except O. sarasinorum, by the presence of a broad reflective silver lateral band extending from the pectoral fin to the end of the caudal peduncle. The presence of a series of dark blotches along the lateral line in males distinguishes O. polylepis from all other Sulawesi species except O. bonneorum, O. dopingdopingensis, O. landangiensis, and O. matanensis (Parenti, 2008; Mandagi et al., 2018; Utama et al., 2022).

Description.—A medium to large Oryzias, maximum length recorded 52.5 mm SL. Body cigar-shaped and elongated, anterior body section cylindrical, posteriorly more laterally compressed (Figs. 1–4). Mouth superior, lower jaw enlarged and protruding far beyond upper jaw. Mouth gape oblique and conspicuously deep (Fig. 2B). Jaws with villiform teeth which are largest in anterior two-thirds of dentary; males with large external conical teeth on upper and lower lips, especially near joints; frequently also with enlarged caniniform teeth on upper and lower jaw tips. Snout length short to medium (26.3–37.6 [32.4]), eyes relatively large (32.6–40.7 [35.9]), especially in relation to short head (23.1–27.3 [25.1]). Dorsal profile straight without arch, ventral profile moderately convex, no defined ventral concavity as in pelvic-brooding species. Caudal peduncle long (17.1 21.1 [18.8]). Pelvic-fin insertion between fourth and fifth pleural rib (Fig. 2B).

Scales are remarkably small and numerous; scale shape varies from cycloid to ellipsoid, with shape changing allometrically, i.e., largest specimens had most vertically stretched ellipsoid scales; not as deciduous as in other congeners. Males with elongated dorsal- and anal-fin rays, relatively small gaps between fin-ray tips and fin-membrane edges (Fig. 4). Long caudal peduncle creating a large gap between end of dorsal- and anal-fin tips and caudal base. Anal-fin shape in females obtuse trapezoid with rounded tips (Figs. 1B, D, 3B, C); males with disproportionally longer anterior anal-fin rays, giving fin edge a concave appearance (Figs. 1A, C, 2–4). Anal and dorsal-fin rays in females comparatively short. Median pelvic-fin rays connected to ventral body by a membrane along about one-fourth to one-third of its length. Caudal-fin edge lunate; pro-current caudal-fin rays long and numerous (5–10/7–11 [7/9]), extending relatively far back onto caudal peduncle, dorsally ending between spinae tips of second- and third-last and ventrally between third- and fourth-last vertebrae (Fig. 2B).

Dorsal-fin rays 11–13 [12]. Anal-fin rays 20–23 [21]. Pelvic-fin rays 6–7 [7]. Pectoral-fin rays 11–14 [13]. Principal caudal-fin rays i,4,5,i. Procurrent caudal-fin rays dorsally 5–10 [7], ventrally 7–11 [9]. Scales in lateral series 79–93 [85]. Vertebrae 30. Branchiostegal rays 5.

Color in life.—General body coloration grayish brown with slight olive-green hue (Figs. 2–4). Ventral body white–translucent. Eyes light blue. Three to nine grayish blotches along lateral line in males, also present in females, but generally fainter or absent (Fig. 3B, C). Dorsal-fin base yellowish-brown. Anal-fin base grayish to yellowish hyaline. Caudal-fin base and caudal-fin margins yellowish to orange. Pectoral fins translucent white in females, with grayish-black pigmentation in males. No vertical stripes along back (cf. O. kalimpaaensis). Prominent luminous band with blue-purplish reflections along the lateral line from pectoral-fin insertion until caudal peduncle. Similar reflective blue shine on operculum.

During courtship, males present a continuous blackish stripe on head and back that becomes progressively narrower posteriorly, similar to related species of Oryzias. The area of the reflective lateral band on lateral body also becomes darker during courtship. Between this band and dorsal stripe, base color brightens up yellowish to greenish golden. Further, dorsal and anal fins become dark gray to blackish, yellow to orange color of caudal-fin margins becomes more brilliant, and blotches along the lateral line become darker and more visible. Blotches are especially prominent in sparring males.

Color in alcohol.—Base color pale brown (Fig. 1). Scales on dorsal flanks and back with blackish pigmentation in posterior half, giving the back a darker brown appearance. A dark gray-brown dorsal stripe progressively narrowing down in width from upper lip until anterior dorsal-fin insertion in males, but also less prominently visible in some females. Narrow blackish mid-lateral stripe from pectoral-fin base to hypural plate. Three to nine round to oval dark brown to blackish lateral blotches in males. Despite being visible in living specimens, blotches are mostly absent in females; only one to two visible in some of the specimens. Ventral body cream to light brown, slightly brighter than base color. Male with very sparse light brown pigmentation along anal-fin base. Dorsal head and snout blackish brown. Throat and ventral snout cream to light brown. Fins translucent; dorsal, anal, and caudal fins with light grayish-brown pigmentation in males, much more vanished in females. Caudal-fin margins and caudal-fin-ray insertion light brown.

Sexual dimorphism.—Similar to other ricefishes, males have elongated, filamentous dorsal- and anal-fin rays (Figs. 1–4). Larger males have a fleshy extension of the dorsal-fin base with a row of larger cycloid scales. Males with more prominent dark blotches along the lateral line and more pronounced pigmentation on the dorsal, anal, and pelvic fins; translucent in females. Both sexes with yellow to orange caudal-fin margins in life, but more prominently in males (Figs. 2A, 3). Adult males with prominent external teeth on the lips; tooth expression most prominent in largest specimens. Body depth is greater in males (16.0–18.4 vs. 18.4–21.4), while females possess longer pelvic fins (10.4–13.8 vs. 9.2–11.7).

Distribution.—Oryzias polylepis is so far known only from the Lariang River drainage, Central Sulawesi, Indonesia that drains westward into the Strait of Makassar. The majority of the watershed is located in remote upland regions, with the upstream half of the Lariang River's main channel situated at altitudes between 1,200 and 400 m MSL (Fig. 5).

At present, this species is known from five sites in two remote highland valleys: three sites in Bada Valley, with two at the Lariang River main channel near Lengkeka Village and Bomba Village (latter uncatalogued specimens; 01°51′10.37″S, 120°16′46.44″E) and one at lower Malei River near the Gintu Village; two sites in Napu Valley at Watutau Village, namely Lariang River and lower Pembangu River, a main tributary of the former in the southern part of the valley (Fig. 5). The species was not recorded in Wuasa River at Wuasa Village (01°25′32.12″S, 120°19′2.23″E), northern Napu Valley, or the Malei River near Runde Village (01°54′12.74″S, 120°14′26.93″E) in southern parts of Bada Valley. We assume that the species is more widespread in the Lariang River drainage, but additional sampling is required for confirmation.

Habitat and ecological notes.—Lariang River near Lengkeka Village, Bada Valley (Fig. 6A, B): This is a large river (width up to 80 m) with moderate to fast flow; ∼200 km upstream of river mouth. The type locality is a narrow pass of the Lariang River (15–25 m wide, >2 m deep) west of the main Bada Valley plain through a short ravine with stronger water current, between two stretches of rapids (Fig. 6A); substrate heterogenous, consisting of light-colored sand, stones, and boulders (Fig. 6B). Abundant driftwood, partial canopy cover, only minor human use in form of small cocoa tree plantations. Underwater visibility <20 cm. Water temperature 27.1°C, pH 8.2, conductivity ∼600 µS. Sympatric native fish species collected are Oryzias kalimpaaensis (Fig. 7) and Lentipes mindanaoensis. Not collected but reported by locals are Anguilla spp., Belobranchus belobranchus (“Bou Ebe”), and two larger fish, known locally as “Patoga” and “Bangkoko,” identified preliminarily herein as Lates calcarifer and Mesopristes cancellatus, respectively. Introduced species include Barbodes binotatus, Osteochilus vittatus, Oreochromis sp., Aplocheilus armatus, Gambusia sp., Poecilia reticulata, and Trichopodus trichopterus.

Lower Malei River at Gintu Village, Bada Valley: Water clear, tea-like stain, underwater visibility >2 m. 25–45 m wide. Substrate diverse, including sand, gravel, and mud-stone boulders. Water temperature 24°C, pH 8.1, conductivity ∼200 µS. Sympatric native fish species recorded are O. kalimpaaensis, L. mindanaoensis, Sicyopterus sp. aff. erythropterus (likely the same species identified as S. erythropterus in Jamonneau et al., 2024), and Anguilla sp. Introduced species were abundant and include Barbodes binotatus, Osteochilus vittatus, Oreochromis sp., Aplocheilus armatus, Gambusia sp., and Poecilia reticulata.

Lariang River at Watutau Village, Southern Napu Valley: 15–30 m wide, up to 2 m deep, ∼270 km upstream of the river mouth. Water visibility <0.5 m. Moderate water flow. Substrate mostly sand, partly muddy in shallower water, riverbank with gravel, rocks, or mudrocks. Abundant crustaceans, including Caridina spp. (especially C. clandestina), Macrobrachium spp., and several species of freshwater crabs. Plenty of overhanging riparian vegetation (e.g., Phragmites karka). The only other native fish species observed was O. kalimpaaensis. Introduced fish species present were Barbodes binotatus, Osteochilus vittatus, Oreochromis sp., Aplocheilus armatus, Gambusia sp., Poecilia reticulata, Channa striata, and Trichopodus trichopterus.

Pembangu River at Watutau Village, Southern Napu Valley (Fig. 6C, D): Major tributary of Lariang River in southern Napu Valley, 5–15 m wide, up to 1 m deep, strongly meandering in its lower course. Moderate to fast waterflow. Substrate heterogeneous, consisting mostly of sand and gravel on mudrock bed. Plentiful overhanging riparian vegetation (e.g., P. karka). Oryzias polylepis was mostly collected close to steeper banks and underneath overhanging reeds (Fig. 6D), often in stronger current. Underwater visibility ∼0.5 m. Co-occurring fish and crustacean species as described for Lariang River in Napu Valley.

Rather atypical for ricefishes, O. polylepis is a strong active swimmer and was always collected in microhabitats with moderate to strong current, usually in deeper waters (water depth >0.5 m). Moreover, it was primarily collected in waters with reduced underwater visibility and, unlike the sympatric O. kalimpaaensis, was consistently absent from smaller tributary streams with clear and cool water. Due to this, fish could not be observed underwater in situ. Aquarium observations revealed a fast and often restless swimming behavior, regularly favoring high current velocity spots. Feces of freshly collected specimens contained remains of phytoplankton. However, under aquarium conditions, they are not selective and were fed on aquatic invertebrates and fish larvae.

Reproductive biology.—Unlike all other endemic Oryzias known from western Central Sulawesi, O. polylepis is a transfer brooder (i.e., it does not carry its eggs connected to the body until hatching of larvae as in pelvic-brooding ricefishes). Traits typically associated with pelvic brooding in females of related species are partially present but less pronounced in O. polylepis. Most prominently, the pelvic fins of female O. polylepis are only slightly enlarged (Figs. 1, 3). The ventral body does not form the distinct concavity seen in pelvic-brooding species. Extended egg-carrying was not observed in females collected in nature or under aquarium conditions. In the aquarium, females carry a cluster of up to ∼15 eggs on the genital pore post-mating and deposit them inside spawning mops (submersed synthetic yarn bundles) after a few hours at most. Eggs are rather large, with diameters of approximately 1.6–1.8 mm. Spawning substrate in nature is unknown. In a typical mating event, males approach females by swimming beside or underneath them; males then briefly tilt their body to the side, which causes the reflective lateral band to flash, possibly signaling conspecifity to the female, before attempting the typical mating clasp also seen in other ricefishes.

Conservation status.—At the time of collection, O. polylepis was abundant at all sites where it was recorded. However, despite its remoteness, the Lariang River watershed is impacted by numerous potentially harmful human activities. These include the release of toxic tailings from gold mining, as reported by locals for several areas in the Lariang River watershed (e.g., by locals from the Bada Valley for areas downstream of the Bada Valley) and by locals in the southern Napu Valley. There are also plans for hydroelectric dam construction along the river (PT Nusantara Infrastructure Tbk, 2015; PT Indonesia Hydro Consult, 2020; Power Technology, 2021) with unknown impacts for O. polylepis, but certain detrimental impacts on diadromous species. The latter are target species for local fishers, and some, like the eleotrid goby Belobranchus belobranchus, also have local cultural importance (Yuniati et al., 2020).

Around one-tenth of the specimens of O. polylepis collected were infested with Lernaea sp., a widespread parasite also seen on other wild Sulawesi ricefishes species (Kottelat, 1990b; Parenti and Soeroto, 2004; Möhring et al., pers. obs., 2019, 2023; Schwarzer et al., pers. obs., 2019; Gani et al., 2022; Herder et al., 2022). Although supporting data are lacking, it appears likely that this parasite was introduced to Sulawesi by stocking of non-native fish species (Kottelat, 1990b; Whitten et al., 2001). The abundance of parasitized specimens in many species all over Sulawesi suggests that ricefishes are particularly susceptible to infestation from Lernaea.

Despite the remoteness of the area, introduced fish species are numerous and widespread in the Lariang basin. Anabas testudineus (“Kosa/Koha”) and Channa striata (“Gabus”) were already reported by Kruyt (1938) from the Besoa Valley, also located within the drainage basin southwest of Napu Valley (Fig. 5), and appear to represent ancient introductions (Whitten et al., 2001). The cyprinid Barbodes binotatus, which was perhaps introduced accidentally with stocking of the larger, co-occurring cyprinid Osteochilus vittatus, or potentially on purpose for mosquito control, is extremely abundant and at many sites (such as the Malei River at Runde Village, and all smaller streams less than 5 m wide visited in Bada Valley) comprised most of the fish biomass. Oreochromis sp. is also widespread, as are Gambusia sp., Poecilia reticulata, and Aplocheilus armatus. Trichopodus trichopterus and Clarias sp. were recorded multiple times. The presence of nationally banned Pterygoplichthys sp. in the Lariang River at Tuare Village, Bada Valley is also worrisome, as this popular ornamental catfish species is known to cause ecological and economic damage when introduced (Page and Robins, 2006; Orfinger and Goodding, 2018; Patoka et al., 2020).

Etymology.—Polylepis—from ancient Greek “polus” (= many), an adjective, and “lepis” (= scale), a noun, in reference to its small and plentiful scales, reflected in high scale counts in lateral series. Compound noun, indeclinable.

Local names: Napu Valley (Bahasa Napu)—“Antowo.” Mainly for Oryzias kalimpaaensis, but no distinction made between species; our information from local villagers in Watutau Village indicate that Antowo is not Aplocheilus armatus (“Kepala Timah”), as was reported in Mondolu et al. (2011). Bada Valley (Bahasa Bada)—“Rono.” Identical to Lindu and Lake Poso (Pamona) areas for Oryzias spp. and smaller Adrianichthys spp.

Phylogenetic relationships.—Oryzias polylepis belongs to a clade of Oryzias restricted to western Central and Southern Sulawesi (Fig. 8A). It is closely related to the sympatric second ricefish species recorded from the Lariang drainage, O. kalimpaaensis, and both species were retrieved in a sister species relationship in the molecular phylogeny based on mitochondrial MT-ND2 sequences. Both species formed monophyletic groups, respectively, and no haplotype sharing was observed, suggesting complete reproductive isolation (Fig. 8B). Within O. polylepis and O. kalimpaaensis, haplotypes did not cluster according to geographic location, and numerous individual haplotypes were shared between specimens from collection sites in Napu and Bada Valleys.