Oryzias chenglongensis, Chen & Lai, 2024

Chen, I-Shiung & Lai, Hong-Thih, 2024, A new ricefish of genus Oryzias (Teleostei: Adrianichthyidae) from western Taiwan, Zootaxa 5550 (1), pp. 320-327 : 321-326

Oryzias chenglongensis new species

( Figs. 1–4 )

Holotype.—NTOUP-2018-06-310; 24.8 mm SL, coll. I-S. Chen ; Chenglong wetland, Yunlin County, Taiwan, ROC.

Paratypes.—NTOUP-2018-06-311; 3 specimens, 23.5–26.6 mm SL, coll. I-S. Chen ; Chenglong wetland, Yunlin County, Taiwan, ROC . NTOUP-2018-02-312, 15.2–24.5 mm SL, 20 specimens, coll. I-S. Chen ; Chenglong wetland, Yunlin County, Taiwan, ROC .

Diagnosis

The new species, Oryzias chenglongensis can be well distinguished from other congeners by the following unique combination of features: (1) fin-ray counts: dorsal-fin rays 6 (6 seen in holotype); anal-fin rays 19–20 (19); pelvic-fin rays 6 (6); pectoral-fin rays 10 (10); principle caudal-fin rays i,4/5,i (i,4/5,i); (2) body compressed laterally with body depth at pelvic origin 24.0–24.3 (24.3), body depth at anal fin origin 15.5–20.4 (20.4); (3) the dorsal-fin origin inserted almost at the vertical of 14 th anal-fin rays, membrane between dorsal-fin 5 th and 6 th rays without distinct notch in adult male; and (4) body translucent, light yellowish green or brown, scattered with minute melanophores, a narrowly dotted, longitudinal black line along the middle forward to vertical above pelvic fin; T-shape black mark of caudal fin base in male; operculum and pre-pectoral region slivery, no any silvery scales on lateral body, lip color grayish or creamy yellow and eye bluish silvery dorsally.

Description

Body proportions as their detailed morphometry were summarized in Table 1 . Dorsal-fin rays 6 (6 seen in holotype); anal-fin rays 19–20 (19); pelvic-fin rays 6 (6); pectoral-fin rays 10 (10); principle caudal-fin rays i,4/5,i (i,4/5,i), and vertebral counts 29–30 (30).

Small species, with maximum size of available specimens examined as 26.6 mm SL. Head moderate large, with head length 22.8–24.5 (22.8) depressed dorsoventrally; eye very large, eye diameter 34.8–41.3 (39.9); snout very short, snout length 22.8–25.9 (22.8). Body compressed laterally, robust anteriorly and slender posteriorly, body depth at pelvic origin 24.0–24.3 (24.3), body depth at anal fin origin 15.5–20.4 (20.4). No greatly pronounced abdominal concavity between pelvic fins and anterior part of anal fin in female. Mouth terminal, up-turned; tip of upper lip about the horizontal line crossing the upper margin of pupil, lower jaw projecting forward beyond upper jaw, each jaws in having minute conical teeth; lips slightly fleshy. Dorsal body profile relatively straight from head to mid-dorsum and curving from mid-dorsum to dorsal-fin origin; ventral profile as a gentle arch from head to anal-fin origin.

Dorsal profile of head concave. Cheek very limited by large eye. Orbit not projecting toward the dorsal profile. Gill slit opening to superior margin of pectoral-fin base; isthmus located inferior to posterior margin of eye.

Scales relatively large and deciduous, cycloid. No scales on rostral zone. Cephalic lateral-line system absent on dorsal, lateral, jugular of head. Nostril opens upper jaw posterosuperior, and lachrymal in front of eye opens near anterior margin.

Dorsal fin situated for posteriorly, the dorsal-fin origin inserted almost at the vertical of 14 th anal-fin rays. Membrane between dorsal-fin 5 th and 6 th rays without distinct notch in adult male. Dorsal fin rays may elongate with growth in male. Pelvic fin abdominal. Anal fin base rather long, 28.3–30.1 (29.8); membrane margin between each anal-fin ray indented in male, somewhat and slightly concave in female. Pectoral fin rays expended medially. Last pelvic-fin ray connected along less than one-half its length to body forming connecting membrane. Caudal fin truncate, median to posterior 1/3 part branched.

Males with a short, tubular urogenital papilla; female with an enlarged bilobed fleshy, urogenital papilla.

Coloration in life

Body translucent, light yellowish green or brown, scattered with minute melanophores can be seen alive and preservative, a conspicuous, narrowly dotted, longitudinal black line along the middle forward to vertical above pelvic fin. T-shape black mark of caudal fin base in male. Belly wall, peritoneum slivery, somewhat subrectangular in both sexes. Operculum and pre-pectoral region slivery. No any silvery scales on lateral body. Lip color grayish or somewhat creamy yellow. Eye bluish silvery dorsally, silvery ventrally with some brilliant yellow dots.

Generally, all fins and belly colored pale white to pale yellow. Caudal fin with yellowish dorsal and ventral submarginal stripes and the stripes darker with melanophores as well as distal yellowish margin in male. Dorsal edge of dorsal and pectoral fins, distal region of pelvic and anal fins with yellow bands. Entire pelvic fin yellowish in male. Pelvic and anal fin with widely scattered tiny melanophores. Caudal fin membrane with about 4 hairline longitudinal stripes.

Coloration while specimens in preservative similar above and all brilliant coloration and translucent part entirely faded, body generally light yellowish brown except the melanophores and some larger deep black marks.

Distribution and habitats

Although the type specimens of Oryzias chenglongensis eventually described and collected from the Yunlin County of western Taiwan, it can be also found from Chairyi and Tainan by some photo image evidences of local people without well preserved specimens. It is highly possible to be an endemic species around Taiwan island.

It can be considered that the brackish ricefish might be existed in the wetlands of western Taiwan (at least ranging from Yunlin southward to Taiwan) although the current population may be very low and rare. This new species merely collected from brackish habitat around 20–30 for salinity. The recorded localities from both Chiaryi and Tainan are also the brackish habitats of wetlands and estuaries. In our breeding experiment, this fish can also survive well in fresh water, it might be more widely distributed around the lowland freshwater to brackish region around Taiwan.

Etymology

The specific name, chenglongensis , is referred to names of the fish holotype locality collected “Chonglong wetland”, western Taiwan although its available geographical range may from Yun-lin, Chiar-yi, to Tai-nan of western Taiwan.

Conservation

Due the very rare of current new species in wild survey in western Taiwan, we only kept very limited individuals into type series. Its habitat has also faced the great ecological threat from at least two invasive species of American killifishes. Almost other fish individuals of new species have been kept for conservation reason and reproduce their further off spring and save its limited stock at NTOU, Keelung for avoiding great aquatic ecological threat from this endangered species becoming extinction.

Figures

FIGURE 1. Oryzias chenglongensis n. sp., male, NTOUP-2018-06-310; 24.8 mm SL, Chenglong wetland, Yunlin County, Taiwan.

FIGURE 2. Oryzias chenglongensis n. sp., female, NTOUP-2018 -06-311, 26.6 mm SL, Chenglong wetland, Yunlin County, Taiwan.

FIGURE 3. Head profile and pigmentation pattern of Oryzias chenglongensis, holotype.

FIGURE 4. Dorsal-fin pigmentation pattern of Oryzias chenglongensis, holotype (above) and Oryzias curvinotus (below).