Oryzias luzonensis
Creators: name: Parenti, Lynne R.
Publisher: name: Zenodo
Year: 2008
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Actinopterygii
Beloniformes
Adrianichthyidae
Oryzias
Oryzias luzonensis

description: ORYZIAS LUZONENSIS (HERRE & ABLAN, 1934)   
PHILIPPINE MEDAKA  
FIGURE 44  
 Aplocheilus luzonensis Herre & Ablan, 1934: 275–277, pl. 1 [type locality: Philippines: Solsona, Ilocos Norte, Luzon Is.].- Blanco, 1947: 89–93 [breeding and embryology].   
 Oryzias luzonensis.- Yamamoto, 1975: 24 [listed].- Formacion & Uwa, 1985: 285–291 [cytogenetic characters and species differentiation].- Sakaizumi, 1985: 521–522 [electrophoretic comparisons].- Uwa, 1986: 867–875 [cytogenetic comparisons].- Ibarra & Stewart, 1987: 10 [FMNH type specimens].- Uwa & Parenti, 1988: 159 [morphometric and cytogenetic comparisons].- Hamaguchi, 1996: 757–763 [description and comparison of testis structure].   
 Differential diagnosis: Oryzias luzonensis is a small ricefish species (largest specimens examined 32.7 mm SL) and member of the biarmed chromosome group of Uwa (1986), along with O. latipes, O. curvinotus and the miniatures O. sinensis and O. mekongensis. These species have anal-fin rays of approximately the same length, forming a ‘parallelogram-shaped’ fin, and chromosome arms numbering 58 or more, reaching the highest recorded number of 96 in O. luzonensis. Oryzias luzonensis and O. latipes are the largest species of this group that also share a mesethmoid ossification that is indented anteriorly in some specimens, and a genome size of 1.9 pg per nucleus or greater. They are like O. curvinotus and differ from the two miniatures by having the first pleural rib on the third rather than the second vertebra in most specimens and paired, bilaterally asymmetric, as opposed to single lobed, testes. They are like the miniatures, and differ from Oryzias curvinotus by having bony processes on the pectoral-fin rays. Oryzias luzonensis has a dorsal fin that is anterior (opposite vertebrae 20–21 as opposed to vertebrae 22–23) and an ethmoid margin that is irregular relative to those of O. latipes.   
 Description: Small, maximum size of specimens examined 32.7 mm SL. Body compressed laterally, body depth 20–24. No pronounced abdominal concavity between pelvic fins and anal fin. Mouth terminal, jaws subequal or lower jaw projecting just 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 20–24; snout length 5–6; eye moderate, 7–9, orbits meet dorsal surface of head. Basal portion of dorsal and anal fin project somewhat beyond primary body profile. Scales relatively large, cycloid; 30–35 in a lateral series. Somewhat filamentous dorsal- and anal-fin rays in males; medial pectoral fin-rays and posterior anal-fin rays with large, 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 irregular, interrupted anteriorly. 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 fourth pleural rib. Caudal skeleton with two epural bones; one ventral accessory bone and a second accessory cartilage or bone. Fifth ceratobranchial toothplates suboval, 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 5–7. Anal-fin rays 15–19. Pelvic-fin rays 6. Pectoral-fin rays 11. Principal caudal-fin rays i,4/5,i. Procurrent fin-rays, dorsal 5, ventral 6. Vertebrae 29–31 (11–12 + 18–19). Branchiostegal rays 5–6.  
 Cytogenetic data: Oryzias luzonensis has a biarmed chromosome constitution, with 2 n = 48 chromosomes, comprising a combination of 24 metacentric and submetacentric pairs; chromosome arm number (NF) totals 96 (Formacion & Uwa, 1985; Table 2). Oryzias luzonensis has the second largest recorded genome size of any Oryzias species, 1.9 pg per nucleus (Table 2).   
 Colour in life: Grey, with yellow sheen dorsally and silvery along sides; dorsal-, anal-, pelvic-fins and dorsal and ventral caudal-fin rays yellowish or hyaline; pectorals hyaline (Herre & Ablan, 1934: 275). Body nearly 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: Ground colour pale yellow to grey, belly pale whitish yellow. A discrete row of melanophores from the dorsal surface of the head to the dorsal-fin origin; dorsal surface of head and lateral surface of body with minute, sparse to dense, dark brown to black chromatophores, larger and more prominent on posterior portion of body of males, and forming scattered spots in some specimens. Females with a subrectangular, males with a smaller, subtriangular dark brown to black peritoneum. Caudal-fin rays of males dusky, dark brown line along proximal half of membranes between median caudal-fin rays; dorsal and anal margins of caudal fin hyaline. Submarginal dark brown band in anal fin of adult males.   
 Distribution and habitat: Endemic to Luzon Is., the Philippines, from creeks and rice fields (Herre & Ablan, 1934). Oryzias luzonensis is the only ricefish endemic to the Philippine archipelago.   
 Remarks: Herre & Ablan (1934: 276) designated a ‘Type: No. 41062, Fish and Game Administration collection, 30 mm in length, and 29 cotypes [= paratypes] from 24–30 mm in length, collected by the junior author from a creek and from rice fields at Solsona, Ilocos Norte, Luzon, Dec 1933. Over 500 living specimens collected at the same time were placed in the Manila Aquarium, Fish and Game Administration, and are under our observation at the time of writing, December 20, 1933. More than 500 alcoholic specimens, 9–30 mm in length, from the same locality, are also in the collection. A few cotypes and other specimens are also in the collection of Stanford University, California.’ The holotype has not been identified in any collection, has probably been destroyed, and is considered lost. No lot of 29 specimens can be identified either. One paratype lot, SU 29079, containing 111 specimens collected by Guillermo L. Ablan from the type locality on 4.xi.1933 was listed by Böhlke (1953: 52). The 112 specimens in this lot at CAS range from 11.8 to 30 mm SL. There are an additional four specimens, FMNH 47042, from this locality, listed by Ibarra & Stewart (1987: 10) as paratypes. Morphometric and meristic data are supplemented by those in Herre & Ablan (1934) and Uwa & Parenti (1988). The local common name for this species in Ilocos is coscosleng (Blanco, 1947).   
 Material examined: 689 specimens (11–32.7 mm).   
Paratypes. PHILIPPINES. Luzon Is.: creek and ricefields at Solsona, Ilocos Norte Prov., CAS-SU 29079, 112 (11.8–30 mm), G. L. Ablan, Oct, 3–4.xi.1933; FMNH 47042, 4.  
Non-type specimens. PHILIPPINES. Luzon Is.: Solsona, Ilocos Norte Prov., CAS-SU 29564, 556 (11– 32.7 mm, 2 of which have been cleared and counterstained, and 12 of which, 21.7–32.0 mm, have been cleared and stained for bone only), A. W. Herre, 12.iv.1934; FMNH 47387, 10 (12.5–29 mm), G. A. Lopez, 12.iv.1934; CAS 58032, 7 (25.1–28.0 mm, 2 of which have been cleared and counterstained), M. J. Formacion & H. Uwa, 16.xii.1982.
description: Published as part of Parenti, Lynne R., 2008, A phylogenetic analysis and taxonomic revision of ricefishes, Oryzias and relatives (Beloniformes, Adrianichthyidae), pp. 494-610 in Zoological Journal of the Linnean Society 154 (3) on pages 567-569, DOI: 10.1111/j.1096-3642.2008.00417.x, http://zenodo.org/record/5446868