Oryzias curvinotus, (NICHOLS & POPE, 1927)

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 : 559-561

ORYZIAS CURVINOTUS ( NICHOLS & POPE, 1927)

HAINAN MEDAKA

FIGURE 40

Oryzias latipes .- Oshima, 1926: 19 [Hainan Is., China].- Harada, 1943 [Hainan Is., China].

Aplocheilus curvinotus Nichols & Pope, 1927: 380 , fig. 43 [type locality: China: Nodoa, Hainan Is.; tentative classification in Oryzias as subgenus of Aplocheilus ].- Nichols, 1943: 234–235 [in subgenus Oryzias ; synonymy; China].

Oryzias curvinotus .- Rosen, 1964: 227 [classification in family Oryziatidae ].- Uwa, Tanaka & Formacion, 1982: 15–17 [karyotype and banding analyses of species probably not O. curvinotus ; see Uwa, 1991a].- Uwa, 1986: 867–875 [cytogenetic comparisons].- Uwa & Parenti, 1988: 159 [morphometric and cytogenetic comparisons, distribution].- Uwa, 1991a: 361–367 [characters and comparisons].- Hamaguchi, 1996: 757–763 [description and comparison of testis structure].- Parenti, 2000b: 600 [listed].- Matsuda et al., 2003: 159–161 [genetics of sex determination and comparison with O. latipes ].

Oryzias cf. curvinotus .- Kottelat, 2001a: 10, 56, fig. 118 [report from Quang Ninh Prov., Vietnam; characters].

Differential diagnosis: Oryzias curvinotus is a member of the biarmed chromosome group of Uwa (1986), along with O. luzonensis , O. latipes and the miniatures O. sinensis and O. mekongensis , distinguished from other ricefishes by having anal-fin rays of approximately the same length, forming a ‘parallelogram-shaped’ fin (as opposed to a subtriangular-shaped fin that tapers posteriorly), and chromosome arms numbering 58 or more (as opposed to 48 or fewer). Oryzias curvinotus is distinguished from these species by lacking bony processes on the pectoral-fin rays. It is like most specimens of O. latipes and O. luzonensis in having the first pleural rib on the third, rather than the second vertebra and paired, bilaterally asymmetric, as opposed to single lobed, testes, and like O. sinensis in having the pelvic fins in line with the third, rather than the fourth pleural rib.

Description: Small, maximum size of specimens examined 27.2 mm SL. Body compressed laterally, body depth 18–23 (specimens dehydrated). No pronounced abdominal concavity between pelvic fins and anal fin. Mouth terminal, jaws subequal or lower jaw projecting slightly beyond upper jaw. Dorsal body profile relatively straight from head to dorsal-fin origin; ventral body profile somewhat convex from head to anal-fin origin. Dorsal surface of head slightly convex just anterior to orbits. Head length 21–26; snout length 5–8; eye moderate, 8–9, orbits meet dorsal surface of head. Basal portion of dorsal and anal fin do not project significantly beyond primary body profile. Scales relatively large, cycloid; 27–28 in a lateral series. Elongate, filamentous dorsal- and analfin rays in males; posterior anal-fin rays with bony contact organs. Medialmost pelvic-fin ray connected to body via a membrane along its proximal portion. Caudal fin truncate. Male with a short, 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 two or three enlarged posterior teeth on the premaxilla and dentary; tooth tips project through lips. No preethmoid cartilage; ossified portions of mesethmoid discshaped; anterior border of ethmoid cartilage straight. 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; 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, one accessory cartilage. Fifth ceratobranchial toothplates subtriangular, with teeth in irregular rows anteriorly, followed by six discrete rows of unicuspid teeth, including a small, incomplete posterior row. Basihyal bone relatively short and triangular, basihyal cartilage extremely elongate and rectangular. Epibranchial elements fully ossified; epibranchial 2 notably smaller than the other epibranchial elements.

Dorsal-fin rays 5–6. Anal-fin rays 17–20. Pelvic-fin rays 6. Pectoral-fin rays 10–11. Principal caudal-fin rays i,4/5,i. Procurrent fin-rays, dorsal 4, ventral 4–5. Vertebrae 28–30 (11–12 + 17–18). Branchiostegal rays 4–5.

Cytogenetic data: Oryzias curvinotus has a biarmed chromosome constitution (See Uwa, 1991a; Table 2). Populations show marked variation in karyology and it is likely that further, detailed analysis will result in the recognition of additional taxa. Oryzias curvinotus specimens from Hong Kong were reported to have 2 n = 48 chromosomes, with four metacentric, 13 submetacentric, five subtelocentric and two acrocentric pairs, and arm number (NF) of 82. Cellular DNA content was estimated at 1.5 pg per nucleus. Specimens from Hainan Island also have 2 n = 48 chromosomes, but differ by having one metacentric, seven submetacentric, 16 subtelocentric and one acrocentric pairs, with an arm number of 64. Karyotype data and banding analyses of specimens identified as O. curvinotus were published by Uwa et al. (1982: 15–17). According to Uwa (1991a: 366), those specimens represent an undescribed species intermediate between O. mekongensis and O. latipes based on inferred chromosomal rearrangements.

Colour in life: Body translucent, and with melanophore pattern as described below in alcohol. Females with a subrectangular, males with a smaller, subtriangular silvery peritoneum and both sexes with a silvery operculum. Caudal fin with yellowish dorsal and ventral submarginal band.

Colour in alcohol: 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 that continues onto the caudal fin on the membrane just dorsal and ventral to the first ray above and below the midline, respectively. Females with a subrectangular, males with a smaller, subtriangular black peritoneum. A faint black line along the anal-fin base. Dorsal-, anal- and pelvic-fin interradial membranes with scattered melanophores.

Distribution and habitat: Widely distributed throughout southern China, including Hainan, Guangdong and Hong Kong, and Vietnam in coastal brackish to freshwater habitats ( Uwa & Parenti, 1988; Kottelat, 2001a).

Remarks: Morphometric and meristic data are supplemented by those in Uwa & Parenti (1988). Another common name for this species is Hainan ricefish.

Material examined: 69 specimens (13.1–27.2 mm SL). Holotype. CHINA. Hainan Is.: Nodoa : AMNH 8398 (male, 23 mm), Third Asiatic Expedition, C. H. Pope, xi.1922 – viii.1923.

Paratypes. CHINA. Hainan Is.: Nodoa : AMNH 14766 , 6 (17.5–19.5), Third Asiatic Expedition, C. H. Pope, xi.1922 – viii.1923 .

Non-type specimens. CHINA. Hainan Is.: Nodoa : AMNH 10493 , 34 (13.1–20 mm, 2 of which have been cleared and counterstained, 5 of which have been cleared and stained solely with alizarin), Third Asiatic Expedition, C. H. Pope, xi.1922 – viii.1923 . Hong Kong: Fan Ling , CAS-SU 61181 , 8 (20– 24.5 mm), R. L. Bolin, 1954, CAS 40759, 4 (21– 24 mm), Hong Kong Survey, 19.iii.1954 . Guangdong Prov., Guangzhou (Canton), Lingnan Univ. , CAS-SU 30248 , 3 (19.1–25.1 mm), A. W. Herre, 14.ii.1934 ; Taiping , CAS-SU 28185 , 10 (14.6–23.5 mm), A. W. Herre, 25.ix.1931 , CAS-SU 39658 , 3 (21.2–27.2 mm), J. L. Gressitt, 14.vii.1936 .

Figures

Figure 40. Oryzias curvinotus (Nichols & Pope, 1927), Hainan Island, China, AMNH 14766, paratype, male, 19.5 mm SL.