Oryzias pectoralis, 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 : 580-581

ORYZIAS PECTORALIS ROBERTS, 1998

PECTORAL- FIN SPOT MEDAKA

FIGURES 15B , 17 , 52

? Oryzias sp. ‘Vietnam’ Stallknecht, 1989: 128 [report of a possibly new ricefish species from Vietnam].

Oryzias pectoralis Roberts, 1998: 221 , fig. 2e [type locality: Laos: Nam Theun Basin, rice paddy near Laksao, Nakai plateau].- Kottelat, 2001a: 10, 56, fig. 119 [report from Quang Ninh Prov., Vietnam; characters].- Kottelat, 2001b: 144, fig. 407 [characters, distribution].

Differential diagnosis: Oryzias pectoralis is a miniature ricefish (largest specimen known is 22.3 mm) that along with O. minutillus , O. uwai and O. setnai comprises a group of four miniatures characterized by a pigmented anal or urogenital region and an elongate caudal fin. Oryzias pectoralis differs from these other miniatures by having bony processes on the anal-fin rays and a larger caudal fin, with i,4/5,i, as opposed to i,3/4,i, principal rays. Oryzias pectoralis and O. mekongensis share a black spot on the dorsal portion of the pectoral-fin base. Oryzias pectoralis is readily distinguished from all other ricefishes by having dense melanophores on the abdominal part of the body, and extremely elongate, somewhat filamentous, caudal-fin rays.

Description: Miniature, maximum size of specimens examined 22.3 mm SL. Body compressed laterally, slender, depth 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 or rounded from head to anal-fin origin. Dorsal surface of head slightly convex just anterior to orbits. Head length 24–26 [24]; snout length 9–11 [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; 32–34 [32] in a lateral series. Dorsal and anal fin slightly rounded, no elongate fin rays; anal-fin rays with bony contact organs in males. Medialmost pelvic-fin ray connected to body via a membrane along its proximal half. Caudal fin extremely elongate and filamentous. Male with short tubular urogenital papilla; female with bilobed urogenital papilla.

Premaxilla short and broad with distinct ascending process; premaxilla and dentary with a single irregular row of caniniform teeth; males with up to three large canine teeth on lateral ramus of the premaxilla and an opposing large tooth on the dentary. No preethmoid cartilage; ossified portions of mesethmoid suboval; 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 in line with third pleural rib. Caudal skeleton with two epural bones; one ventral accessory bone and one accessory cartilage. Fifth ceratobranchial toothplate triangular, with anterior teeth in irregular rows anteriorly, followed by four discrete rows of unicuspid teeth, and no incomplete posterior row. Basihyal bone triangular, basihyal cartilage extremely elongate and rectangular. Epibranchial elements fully ossified; epibranchial 2 absent.

Dorsal-fin rays 6–7. Anal-fin rays 19–20. Pelvic-fin rays 6. Pectoral-fin rays 9–10. Principal caudal-fin rays i,4/5,i. Procurrent fin-rays, dorsal 3, ventral 3. Vertebrae 30–32 (10–11 + 19–21). Branchiostegal rays 5.

Cytogenetic data: Unknown.

Colour in life: Unknown.

Colour in alcohol: Ground colour pale straw. A diffuse row of melanophores from dorsal surface of the head to the dorsal-fin origin, a midlateral black line from the head to base of the caudal fin continues onto the caudal fin on the membrane just dorsal and ventral to the first ray above and below the midline, respectively. A faint black line along the anal-fin base. Dorsal and anal fin interradial membranes with scattered melanophores. Body covered with minute melanophores, most dense on abdomen. Discrete black blotch on dorsal half of pectoral-fin in both sexes. Perianal melanophores and discrete black blotch on base of first several anal-fin rays in some specimens.

Distribution and habitat: Nam Theun watershed (Mekong basin), Laos, and Quang Ninh Province, Vietnam, in rice paddies, swamps and sheltered areas of slow flowing rivers ( Roberts, 1998; Kottelat, 2001a, b).

Remarks: Roberts (1998) noted that although this species was described from a single collection from the Nam Theun basin, it is likely to be more widely distributed in Laos, and possibly also Vietnam. Kottelat (2001a) reported O. pectoralis from Quang Ninh Province, Vietnam, but did not provide museum catalogue numbers.

Material examined: Nineteen specimens (16.1– 22.3 mm SL).

Holotype. LAOS. Nam Theun basin: rice paddy near Laksao, Nakai plateau, CAS 92320 (male, 21.1 mm), T. R. Roberts, 19.xi.1995.

Paratypes. LAOS. Nam Theun basin: CAS 92321, 18 (16.1–22.3 mm, 4 of which have been cleared and stained solely with alizarin, 4 of which have been cleared and stained solely with alcian blue; 1 of which has been cleared and counterstained), collected with the holotype .

Figures

Figure 15. A, Oryzias mekongensis, USNM 268540, holotype, male, 13.0 mm SL. B, Oryzias pectoralis, CAS 92321, paratype, male, 20.1 mm SL. Arrows point to blackish spot at pectoral-fin base in each species.

Figure 17. Oryzias pectoralis, CAS 92321, paratype, male, 19.0 mm SL. Lateral view of midbody. Note perianal melanophores (left arrow) and black blotch on anterior base of anal fin (right arrow). Anterior is to the left.

Figure 52. Oryzias pectoralis Roberts, 1998, Nam Theun basin, Laos, CAS 92321, paratype, female, 17.5 mm SL.