Rhinogobius immaculatus, a new species of freshwater goby (Teleostei: Gobiidae) from the Qiantang River, China

A new freshwater goby, Rhinogobius immaculatus sp. nov., is described here from the Qiantang River in China. It is distinguished from all congeners by the following combination of characters: second dorsal-fin rays I, 7–9; anal-fin rays I, 6–8; pectoral-fin rays 14–15; longitudinal scales 29–31; transverse scales 7–9; predorsal scales 2–5; vertebrae 27 (rarely 28); preopercular canal absent or with two pores; a red oblique stripe below eye in males; branchiostegal membrane mostly reddish-orange, with 3–6 irregular discrete or connected red blotches on posterior branchiostegal membrane and lower operculum in males; caudal-fin base with a median black spot; and no black blotch on anterior part of first dorsal fin in males.


MATERIALS AND METHODS
Specimens for morphological examination were initially preserved in 6% formalin for seven days, and then transferred into 70% ethanol for permanent storage.
Methods for morphometric measurements and meristic counts followed Nakabo (2002), with exceptions as indicated: Standard length (SL), head length, snout length, predorsal length, and preanal length were measured from the tip of the upper lip; Head depth and width were taken at the posterior margin of the preopercle; Body depth and width were taken at the origin of the anal fin. Vertebrae were counted from radiographs using the Kodak DXS 4000 system, and 3D reconstructed CT scans were made with the NSI-x50 system. Notations of cephalic sensory-canal pores and sensory-papillae rows followed Akihito et al. (2002) and Suzuki et al. (2017). Examined specimens in this study were deposited in the Biological Museum, Fudan University, Shanghai (FDU) and Shanghai Ocean University, Shanghai (SOU/SFU/SFC).  (27) and preopercular canal pores (2 or 0 vs. 2), but differing by fewer pectoral-fin rays (14-15 vs. 17-18), fewer anal-fin rays (I, 6-7 vs. I, 8), fewer transverse scales (7-9, modally 8 vs. 9-10), absence of a black blotch on anterior part of first dorsal fin in males (vs. present), and branchiostegal membrane mostly reddish-orange, with irregular blotches posteriorly in males (vs. with red stripes).

Description:
The morphometric and meristic data of the holotype and paratypes are shown in Table 1. The following features can describe the new species: Body cylindrical anteriorly and compressed posteriorly. Head sub-cylindrical. Eye large, dorsolateral. Mouth oblique, with lower jaw tip anterior-most, jaw forming 45 • angel with body axis; corner of mouth reaching below anterior margin of orbit in adult males, not reaching below anterior margin in females. Vertebral counts 11+16=27 (10) or 11+17=28 (1) (Figure 2).   First dorsal-fin rays V-VI (modally VI); second dorsal-fin rays I, 7-9 (modally I, 8); anal-fin rays I, 6-8 (modally I, 7); pectoral-fin rays 14-15 (modally 15); pelvic-fin rays I, 5; segmented caudal-fin rays 9+8, including branched rays 7+7; dorsal procurrent rays 6-8, ventral procurrent rays 5-7. First dorsal fin with third or fourth spine longest, no filamentous spines; rear tip not reaching origin of second dorsal fin when depressed in both sexes. Second dorsal and anal fins short-based, tip of depressed rays far from dorsal and ventral origins of procurrent caudal-fin rays. Origin of anal fin inserted below base of third and fourth rays of second dorsal fin. Pectoral fin elliptical, central rays longest; rear extension far from vertical of anus when depressed. Pelvic fin disc rounded. Rear edge of caudal fin rounded.
Head pores present. Nasal extension of anterior oculoscapular canal with terminal pores B' at vertical between anterior and posterior nostrils. Anterior interorbital section of oculoscapular canal separated, with paired pore C. Single pore D in posterior interorbital region. Postorbital region with paired pore E. Lateral section of anterior oculoscapular canal with anterior pore F and terminal pore H'. Posterior oculoscapular canal short, reduced (absent in 14 specimens), with two terminal pores K' and L'. Gap between anterior and posterior oculoscapular canals larger than length of posterior oculoscapular canal.
Preopercular canal short, reduced (absent in eight specimens), with two terminal pores M' and O'. Sensory-papillae row a short, with two or three papillae below orbit. Row b short, about half length of orbit. Rows c and d longer, not extending to vertical line of rear margin of orbit. Single cp papilla. Row f paired ( Figure 3).

Color in life:
Ground color light brown. Snout with pair of reddish brown stripes united at tip of snout. A reddish oblique stripe below eye in males, not reaching rear edge of mouth; obscure in females. Cheek and opercle with irregular reddish lines, branchiostegal membrane mostly reddish-orange, with 3-6 irregular discrete or connected red blotches on posterior branchiostegal membrane and lower operculum in males; absent in females.
Flank with 6-7 irregular discrete or connected black blotches. First dorsal fin with 3-4 rows of interphased black and white spots. A black blotch on anterior part of first dorsal fin absent in both sexes. Second dorsal fin with 4-5 rows of interphased black and white spots. Pectoral fin proximally white, posterior part with 3-4 rows of interphased black and white spots. Pectoral-fin base with irregular blackish pigmentation, usually darker in upper part. Caudal fin with 5-6 rows of interphased black and white spots. Caudal-fin base with a median black blotch. Pelvic fin and anal fin with slight irregular black pigmentation ( Figures 4A-B, 5).

Distribution and ecology:
Known only from streams of the Qiantang River basin in Zhejiang and Anhui Provinces, China ( Figure 6). Most often found in shallow (10-50 cm deep) low-gradient streams, with sand and gravel mixed substrate.
Adult Rhinogobius immaculatus sp. nov. are small in size. The smallest female with mature oocytes was 22.4 mm SL. The largest specimen collected in the field was 26.3 mm SL. The largest captive specimen kept in an aquarium for 29 months was 32.8 mm SL.

Etymology:
The specific name, immaculatus, is derived from Latin in (without) and maculatus (spotted), an adjective, alluding to the absence of a black blotch on the anterior part of the first dorsal fin in adult males.

DISCUSSION
Number of vertebrae is frequently used for species identification in the genus Rhinogobius Huang et al., 2016;Lee & Chang, 1996;Suzuki et al., 2017;Takahashi & Okazaki, 2017;Yang et al., 2008). Among the current 74 valid species in Rhinogobius, 36 possess 27 or more vertebrae (Huang et al., 2016), as also found in the newly described species, and 28 possess less than 27 vertebrae (Suzuki et al., 2016(Suzuki et al., , 2017Takahashi & Okazaki, 2017). The vertebral number of the remaining species remains unknown.

COMPETING INTERESTS
The authors declare that they have no competing interests.

AUTHORS' CONTRIBUTIONS
J.K.C. designed the study. F.L. and S.L. wrote the manuscript. All authors read and approved the final manuscript.