Oryzias nebulosus, PARENTI & SOEROTO, 2004

Parenti, Lynne R., 2008, A phylogenetic analysis and taxonomic revision of ricefishes, Oryzias and relatives (Beloniformes, Adrianichthyidae), Zoological Journal of the Linnean Society 154 (3), pp. 494-610 : 576-577

ORYZIAS NEBULOSUS PARENTI & SOEROTO, 2004

NEBULOUS RICEFISH

FIGURE 49

Oryzias nebulosus Parenti & Soeroto, 2004: 10 , 14–17, figs 5, 7, 8 [type locality: Indonesia: Sulawesi, Lake Poso ].

Differential diagnosis: Oryzias nebulosus shares with O. nigrimas , also from Lake Poso, a unique sexual dichromatism in preserved specimens: adult males are dark grey to black, whereas females are a lighter greyish yellow to brown. Relative to O. nigrimas , O. nebulosus is a small (maximum size 33 mm as opposed to 51 mm SL), relatively deep-bodied species (body depth 20–25, as opposed to 18–22% SL), with fewer precaudal vertebrae (11–13 vs. 13–14). These last three characters are shared with the Malili Lakes buntingi, O. marmoratus , O. matanensis and O. profundicola , from which O. nigrimas is readily distinguished by colour pattern and by having a lunate, rather than truncate, caudal fin.

Description: Small, maximum size of specimens examined 33 mm SL. Body short, relatively deep; body depth 20–25 [25]. No pronounced abdominal concavity between pelvic fins and anal fin. Mouth terminal, jaws subequal, lower jaw projects slightly beyond upper jaw. Dorsal body profile relatively straight from head to dorsal-fin origin; ventral body profile convex from snout to anal-fin origin. Dorsal surface of head slightly concave just anterior to orbits. Head length 22–25 [23]; snout length 6–8 [6]; eye moderate, 7–9 [7], orbits meet dorsal surface of head. Basal portion of dorsal and anal fin project slightly beyond primary body profile. Scales of moderate size, cycloid and somewhat deciduous; 32–36 [34] in a lateral series. Elongate, filamentous dorsal- and anal-fin rays in males; anal-fin rays without bony contact organs. Medialmost pelvic-fin ray connected to body via a membrane along its proximal half. Caudal fin lunate, dorsal and ventral segmented caudal-fin rays just slightly longer than middle rays. Male with short, slightly conical, tubular urogenital papilla; female with small, bilobed urogenital papilla.

Premaxilla short and broad with distinct ascending process; premaxilla and dentary with two irregular rows of caniniform teeth; males with irregular row of external conical teeth on the upper and lower oral jaws, and one large and two small conical teeth on posterior ramus of the premaxilla. No preethmoid cartilage; ossified portions of mesethmoid discshaped; anterior border of ethmoid cartilage irregular. No flanges on the ventral surface of the palatine and the quadrate. Dorsal ramus of hyomandibula not distinctly bifid, single cartilage articulates with sphenotic and pterotic. Lacrimal sensory canal carried in open bony groove. First pleural rib on parapophysis of third vertebra (rudimentary rib on second vertebra in some specimens); first epipleural bone attaches to parapophysis of first vertebra dorsal to, and not in horizontal line with, posterior epipleural bones; lateral process of pelvic bone attaches to third pleural rib. Caudal skeleton with two epural bones; one ventral accessory bone. Procurrent caudal-fin rays hooked slightly at their base. Fifth ceratobranchial toothplates subtriangular, with pavement dentition anteriorly, followed by four to five discrete rows of unicuspid teeth; small, incomplete posterior row. Basihyal bone elongate, triangular, basihyal cartilage extremely elongate and rectangular. Epibranchial elements fully ossified; epibranchial 2 notably smaller than the other epibranchial elements.

Dorsal-fin rays 9–11 [10]. Anal-fin rays 21–22 [22]. Pelvic-fin rays 6 [6]. Pectoral-fin rays 9–11 [11]. Principal caudal-fin rays i,4/5–6,i. Procurrent fin-rays, dorsal 5, ventral 6. Vertebrae 30–32 (11–13 + 18–20). Branchiostegal rays 5.

Cytogenetic data: Unknown.

Colour in life: Live colour of O. nebulosus was not recorded at capture. As this species has been confused in collections with O. nigrimas , with which it shares a similar, unique preserved colour pattern, both species probably share general characteristics of colour in life (see Kottelat, 1990a: 53–54, and description of O. nigrimas , below).

Colour in alcohol: Ground colour yellowish-grey, belly pale yellow. Pigmentation variable in preserved specimens from pale yellowish overall in smaller specimens to dark brown to black in large males. Dorsal surface of head and dorsal and lateral surface of body with dense dark brown to black chromatophores. A diffuse row of melanophores from the dorsal surface of the head to the dorsal-fin origin, a midlateral black line from the head to base of the caudal fin. Females and lighter-coloured males with diffuse line of dark brown to black chromatophores dorsal from just posterior to anal-fin origin, along body just dorsal to anal-fin base to middle of caudal peduncle. Urogenital papilla heavily pigmented in gravid female, pale grey in other specimens. Fins dusky to dark brown or black, more heavily pigmented in males.

Distribution and habitat: Eastern shore of Lake Poso and its tributary stream, the Poso River, at Tentena, Sulawesi Tengah, Indonesia ( Parenti & Soeroto, 2004: fig. 1). Specimens were collected in the morning by seine and dip nets in clear water over a bottom of sand, pebbles and fallen branches, and at night using kerosene lamps and dip nets from a boat that travelled along the lake shore, including the mouth of the tributary stream. Many of the specimens are infested with parasitic copepods.

Remarks: The sexual dichromatism of O. nebulosus and O. nigrimas , in which males are dark brown to black and females are pale yellow to grey, is characteristic also of Nomorhamphus celebensis , from Lake Poso (see Kottelat et al., 1993), and N. towoetii , from lakes Poso and Towuti (see Meisner, 2001: 261). Data were augmented by those in Kottelat (1990a).

Material examined: 37 specimens (22.3–33 mm SL).

Holotype. INDONESIA. Sulawesi Tengah: Lake Poso at Peura , eastern shore of lake approx. 10 km S of Tentena, L. R. Parenti, K. D. Louie, P. Beta, et al., 13.viii.1995, MZB 11649 (adult male, 32.5 mm).

Paratypes. INDONESIA. Sulawesi Tengah: MZB 11650 22 (22.3–32.9 mm, 6 of which have been cleared and counterstained), collected with the holotype; Lake Poso , eastern shore approx. 17 km S of Tentena , USNM 367129 5 (27.5–33.0 mm, 1 of which has been cleared and counterstained), L . R. Parenti, K. D. Louie, P. Beta et al., 12.viii.1995; Lake Poso, west bank of Poso R. where it empties into lake at Pamona Caves , USNM 354692 , 9 (24.5–31.7 mm), L . R. Parenti, K. D. Louie, P. Beta, et al., 13.viii.1995 .

Figures

Figure 49. Oryzias nebulosus Parenti & Soeroto, 2004, Lake Poso, Sulawesi Tengah, Indonesia, MZB 11649, holotype, male, 32.5 mm SL.