Oryzias uwai, ROBERTS, 1998

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 : 591-592

ORYZIAS UWAI ROBERTS, 1998

UWA’ s MEDAKA

FIGURES 16A , 20B , 58

Oryzias minutillus .- Uwa et al., 1988: 332–339 [in part, Rangoon; distribution, comparison with O. minutillus and specimens of O. latipes referred here to O. sinensis ].

Oryzias uwai Roberts, 1998: 218–219 , fig. 2c [type locality: Myanmar: Rangoon, Irrawaddy and Sittang basins].

Differential diagnosis: Oryzias uwai is a miniature ricefish (largest specimen known is just 16.1 mm SL), hypothesized to be closely related to Oryzias minutillus and O. setnai with which it shares i,3/4,i rather than i,4/5,i principal caudal-fin rays, a medial extension of the ethmoid cartilage, and anterior anal-fin rays elongate, set off from the rest of the fin, and from which it differs by having larger pelvic fins, with six rather than five rays in most specimens. Oryzias uwai and O. setnai share an interrupted, horizontal dark brown bar that runs from the eye to the lower jaw; a mesethmoid that is uniquely subrectangular, rather than round or oval; and a first epibranchial that is cartilaginous, not ossified. Four miniatures, O. uwai , O. pectoralis , O. setnai and O. minutillus , have a pigmented anal or urogenital region and an elongate, rounded caudal fin, a character also of O. hubbsi and O. mekongensis .

Description: Miniature, maximum size of specimens examined 16.1 mm SL. Body compressed laterally, slender, body depth 21–24 [24]. No pronounced abdominal concavity between pelvic fins and anal fin. Mouth terminal, lower jaw projecting slightly beyond upper jaw. Dorsal body profile relatively straight from head to dorsal-fin origin; ventral body profile slightly convex from head to anal-fin origin. Dorsal surface of head slightly convex just anterior to orbits. Head length 29–30 [30]; snout length 9–10 [10]; eye moderate to large, 8–10 [10], orbits meet dorsal surface of head. Basal portion of dorsal fin projects slightly beyond primary body profile. Scales relatively large, cycloid; 26–27 [27] in a lateral series (scale count approximate). Dorsal and pectoral fins elongate, anal fin slightly rounded; anal-fin rays without bony contact organs. Medialmost pelvic-fin ray connected to body via a membrane along its proximal half; pelvic fins large, extend to or beyond anal fin origin in females. Caudal fin with elongate middle rays. Male with short tubular urogenital papilla; female with bilobed urogenital papilla.

Premaxilla short and broad with barely distinct ascending process; premaxilla and dentary with a single irregular row of caniniform teeth; no large canine teeth on lateral ramus of the premaxilla or dentary of males. No preethmoid cartilage; mesethmoid cartilaginous or weakly ossified, when ossified, mesethmoid small and suboval; ethmoid cartilage rectangular with anterior projection. 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 second vertebra; first epipleural bone attaches to second vertebra; lateral process of pelvic bone in close association with third or fourth pleural rib. Caudal skeleton with two epural bones; one ventral accessory bone. Anteriormost dorsal and ventral procurrent rays hooked at base. Fifth ceratobranchial toothplate triangular, with teeth in irregular rows anteriorly, followed by two discrete rows of unicuspid teeth, and no incomplete posterior row. Basihyal bone triangular, basihyal cartilage extremely elongate and rectangular. Epibranchial 1 cartilaginous; epibranchial 2 notably smaller than the other epibranchial elements.

Dorsal-fin rays 6–7. Anal-fin rays 18–21. Pelvic-fin rays 6. Pectoral-fin rays 7–8. Principal caudal-fin rays i,3/4,i. Procurrent fin-rays, dorsal 4, ventral 5. Vertebrae 25–28 (9–10 + 16–18). Branchiostegal rays 4.

Cytogenetic data: Karyotype data for O. minutillus from Thailand were reported by Uwa et al. (1988). Although they referred the now type specimens of O. uwai (then all CAS-SU 40208) to O. minutillus , they had no fresh Myanmar specimens from which karyotype data could be obtained.

Colour in life: Unknown.

Colour in alcohol: Ground colour pale straw. 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, continues faintly onto the caudal fin on the membrane just dorsal and ventral to the first ray above and below the midline, respectively. An interrupted, horizontal dark brown stripe from the eye to the tip of the lower jaw, faded or indistinct in larger specimens. A faint black line along the anal-fin base. Dorsal and anal fin interradial membranes with faint scattered melanophores or hyaline. Perianal region with dense brown to black spot. Pectoral and pelvic fins hyaline. Body with small melanophores.

Distribution and habitat: Irrawaddy, Rangoon and Sittang basins, Myanmar.

Material examined: 118 specimens (8.6–16.1 mm SL). Holotype. MYANMAR. Rangoon: CAS-SU 40208 , holotype (male, 16.1 mm), A. W. Herre, xi.1940.

Paratypes. MYANMAR. Rangoon: CAS-SU 69787 19 (12.2–15.9 mm), collected with the holotype ; Sittang R. drainage, Dayame Chaung, 1.5 km. N of Daik-U., T. R. Roberts , 9.iii.1985 ; Pegu Div., CAS 60739, 6 (12.4–13.8 mm) ; Mandalay rice paddies, T. R. Roberts, 20–24.iv.1993, CAS 92309, 20 (8.6–13.5 mm, 7 of which, 9.3–11.6 mm, have been cleared and stained solely with alizarin) ; Sittang basin, backwater of Bai Nar Chaung near Dabeinzu, K. E. Witte, 4.iv.1996, CAS 92310, 72 (8.8–15.9 mm, 10 of which, 10.2– 14.8 mm, have been cleared and stained solely with alizarin, 4 of which, 12–13.5 mm, have been cleared and counterstained) .

Figures

Figure 16. A, Oryzias uwai, CAS 92309, paratype, female, 13.0 mm SL; B, Oryzias setnai, USNM 277482, female, 17.5 mm SL. Arrows point to interrupted, horizontal dark brown bar from the eye to the tip of the lower jaw in O. uwai, and to the posterior extent of the lower jaw in O. setnai.

Figure 20. A, Oryzias setnai, USNM 277482, 14.5 mm SL; B, O. uwai, CAS 92310, 12 mm SL; C, O. minutillus, CAS 58022, 11 mm SL. Anterior portion of skull and jaw and jaw suspensorium. Arrow points to the medial anterior extension of the ethmoid cartilage. Scale bar = 0.5 mm.

Figure 58. Oryzias uwai Roberts, 1998, Sittang basin, Myanmar, CAS 92310, paratype, male, 10.6 mm SL.