Rhinogobius yaima, Suzuki & Oseko & Kimura & Shibukawa, 2020

Suzuki, Toshiyuki, Oseko, Naoharu, Kimura, Seishi & Shibukawa, Koichi, 2020, Rhinogobius, Bulletin of the Kanagawa Prefectural Museum (Natural Science) 49, pp. 7-28 : 8-15

Rhinogobius yaima sp. nov.

(New Standard Japanese name: Yaima-hirayoshinobori)

( Figs. 1–6 ; Tables 1 & 3 )

Rhinogobius brunneus (not of Temminck & Schlegel): Nakayama, 1975: 114 (in part: Iriomote-jima Island of Yaeyama Group, the Ryukyu Islands, Japan); Hayashi, 1984: 259 (Ishigaki-jima and Iriomote-jima islands of Yaeyama Group, the Ryukyu Islands, Japan).

Rhinogobius sp. DL: Kawanabe & Mizuno, 1989: 589 (in part: Ishigaki-jima and Iriomote-jima islands of Yaeyama Group, the Ryukyu Islands, Japan); Akihito et al., 1993: 1080 (in part: the Nansei Islands, Japan); Akihito et al., 2000: 1252 (in part: the Nansei Islands, Japan); Akihito et al., 2002: 1252 (in part: the Nansei Islands); Suzuki et al., 2004: 450 (in part: Ishigaki-jima and Iriomote-jima islands of Yaeyama Group, the Ryukyu Islands, Japan); Akihito et al., 2013: 1454 (in part: Ishigaki-jima and Iriomote-jima islands of Yaeyama Group, the Ryukyu Islands, Japan).

Holotype. KPM-NI 53486 (formerly OMNH-P 43167 ), male, 60 mm SL, Nakara-gawa River , Iriomote-jima Island of Yaeyama Group, the Ryukyu Islands, Japan, 24°19' 36.97"N 123°47'57.38"E, 31 July 2015, Fig. 1 .

Paratypes. Total 15 specimens (eight males and seven females, 30.2–66.2 mm SL), collected from Yaeyama Group of the Ryukyu Islands, Japan. Iriomote-jima Island: KPM-NI 53487 (formerly OMNH-P 43503 ), female, 51.1 mm SL, O’omija-gawa River, 24°23'24.97"N 123°51'56.97"E, 26 July 2016 , Fig. 2 ; OMNH-P 31934 and 31935, male and female, 55.6 and 66.2 mm SL, stained with Alizarin Red S, Urauchi-gawa River , 24°21' 18.51"N 123°48'23.77"E, 08 October 2006 ; OMNH-P 40036 , male, 46.8 mm SL , same locality with OMNH-P 31934 , 28 March 2012 ; OMNH-P 43166 , male, 66.0 mm SL, collected with the holotype ; OMNH-P 43686–43688 , two males and a female, 37.1–60.6 mm SL, stained with Alizarin Red S, Urauchi-gawa River , 24°21'25.60"N 123°48'12.37"E, 10 August 1993 ; SPMN-PI 45461 and 45462 (formerly OMNH-P 44254 and OMNH-P 44255 ), male and female, 45.7 and 62.9 mm SL, Urauchi-gawa River , 24°21'25.51"N 123°48'12.69"E, 30 July 2019 . Ishigaki-jima Island : OMNH-P 43854 , male, 47.3 mm SL, stained with Alizarin Red S, Ara-kawa River, 24°26'48.73"N 124°10'46.46"E, 18 August 1991 ; OMNH-P 43855 , female, 43.2 mm SL, stained with Alizarin Red S , same locality with OMNH-P 43854 , 19 August 1993 ; URM-P 48739–48741, two males and a female, 30.2–40.8 mm SL, a freshwater stream near Kabira , 21 February 2019 .

Diagnosis. Rhinogobius yaima is distinguished from all congeneric species by the following combination of features: head depressed, its maximum depth 65.5–71.6 % of its maximum width; body and caudal peduncle elongate, their depths 13.8–14.5% SL at anal fin origin and 11.4–12.2 % SL, respectively; 40–43 longitudinal scales; 10+16=26 vertebrae; six spines in first dorsal fin; first dorsal fin low in males, not extending posteriorly to origin of second dorsal fin when adpressed; fifth pelvic-fin segmented ray usually divided into five branches at its first (most proximal) segmenting point; pectoral-fin base and prepelvic area naked; belly with small cycloid scales except for a narrow area around ventral midline; sensory-papillae rows on cheek arranged longitudinally, with no transverse rows; a distinct dull orange oval spot on base of pectoral fin; two orange stripes on temporal region, reaching posteriorly to, or around, a vertical through origin of second dorsal fin; four vertical rows of bright orange dots on caudal fin in males; a pair of vertically-arranged, rounded or rectangular black blotches at base of caudal fin in females when alive or freshly collected.

Description. Dorsal-fin rays VI-I, 7 (1), VI-I, 8* (12) or VI-I, 9 (1); anal-fin rays I, 7 (1) or I, 8* (13); pectoral-fin rays 19* (1), 20 (7), 21 (4), or 22 (2); pelvic-fin rays I, 5* (14); segmented caudal-fin rays (upper part + lower part) 9+8* (14); branched caudal-fin rays (upper part + lower part) 7+7* (11), or 8+7 (3); longitudinal scales 40 (4), 41 (5), 42* (3), or 43 (2); transverse scales 10 (2), 11 (3), 12* (7), or 13 (2); scales between origin of dorsal fin and dorsal insertion of pectoral fin 9 (4), 10* (7), 11 (2), or 12 (1); predorsal scales 0 (1), 5* (3), 6 (3), 8 (1), 10(1), 13(2), 14(1), 15(1), or 17 (1); P-V 3/22110/9* (11); vertebrae (abdominal vertebrae + caudal vertebrae) 10+16=26* (11).

Proportional measurements based on holotype and five paratypes ( KPM-NI 53487, OMNH-P 40036, 43166, SPMN-PI 45461, 45462) are given in Table 1 . Body slender, almost cylindrical anteriorly, compressed posteriorly. Head moderately large, depressed. Snout nearly pointed and long, longer than eye diameter; snout length of males greater than that of females. Eye large, dorsolateral on head, located slightly behind a vertical through midpoint between snout tip and posterior margin of preopercle. Cheek somewhat bulbous, fleshy. Lips thick and fleshy; upper lip slightly protruding anteriorly beyond lower lip; gape slightly oblique; posterior margin of lower jaw not extending posteriorly to a vertical through anterior margin of eye. Anterior naris a short tube without skin flap at its tip, usually located slightly before the midpoint between snout tip and anterior margin of eye; posterior naris a round pore with low rim, closer to anterior naris than to eye. Gill opening extending anteriorly to a vertical through posterior margin of preopercle. Gill membranes broadly attached to isthmus. No fleshy papillae or finger-like projections on lateral margin of shoulder girdle. Tongue free from floor of mouth, with rounded anterior margin. Genital papillae cone-shaped in males and oval in females.

Origin of first dorsal fin slightly behind a vertical through dorsal insertion of pectoral-fin; first dorsal fin trapezoid and slightly higher than second dorsal fin in males, whereas, in females, semicircular or trapezoid, and subequal to second dorsal fin in height; second or third spine longest; all dorsal-fin spines slender and flexible, not filamentous; posterior tip of first dorsal fin (usually distal tip of fourth and, fourth, fifth or sixth spines in males and females, respectively) not extending to origin of second dorsal fin when adpressed. First and second dorsal fins not continued by membrane; all segmented dorsal-fin rays branched; sixth or seventh, and second or third branched rays longest in males and females, respectively; posterior tip of second dorsal fin not extending to caudal fin when adpressed; posterior end of base of second dorsal fin above posterior end of anal-fin base. Origin of anal fin usually below a space between bases of first and third second dorsal-fin branched rays; anal fin slightly lower than second dorsal fin in height; all segmented anal-fin rays branched; fifth, sixth, or seventh, and fifth branched rays longest in males and females, respectively; posterior tip of anal fin not extending to caudal fin when adpressed. Pectoral fin oval; pectoral fin extending posteriorly to a vertical through a space between base of fifth spine and posterior end of base of first dorsal fin; pectoral-fin rays branched, except for dorsalmost and/or ventralmost ray(s) unbranched. Pelvic fins fused medially by well-developed frenum (between spines) and connecting membrane (between innermost rays), forming a circular cup-like disc at least in large adults; pelvic fins extending posteriorly to a vertical through a space between bases of third and fourth first dorsal-fin spines, and not reaching to anus; in three small paratypes (36.4–40.8 mm SL), pelvic fins forming an oval cup-like disc, and extending posteriorly to a vertical through a space between bases of fourth and sixth spines, and not reaching to anus; pelvic-fin spine with a rounded membranous lobe at its tip; all segmented rays of pelvic fin branched; fifth segmented pelvic-fin ray divided into five (may be four in smaller specimens) branches at its first (most proximal) segmenting point ( Fig. 3A ); in three small paratypes (40.8–47.3 mm SL), the number of the branches of fifth segmented pelvic-fin ray is four, but the most inner branch immediately bifurcated. Caudal fin elliptical or fan-shaped.

Scales on body largely ctenoid, becoming smaller anteriorly; a part of basal region of caudal fin, anterodorsal part of body before a diagonal line from a space between origin and end of second dorsal-fin base to dorsal insertion of pectoral fin, and belly with small cycloid scales; scaled area of belly not extending anteriorly to pelvic-fin insertion. Predorsal squamation usually with trifurcate anterior edge; mid-anterior extension extending anteriorly to a space between transverse lines through a point slightly before origin of first dorsal fin and sensory-canal pore K'; anterior extensions of lateral sides extending anteriorly to a transverse line through posterior oculoscapular canal ( Fig. 3B ). The other part of head, pectoral-fin base, pelvic-fin axil and following narrow triangular area around ventral midline of belly ( Fig. 3C ), and prepelvic area naked.

Cephalic sensory systems are illustrated in Fig. 4 . Nasal extension of anterior oculoscapular canal with terminal pore B' located above anterior naris. Anterior interorbital sections of anterior oculoscapular canal separated bilaterally, with paired pore C and a single pore D. Pore E present just behind posterior edge of eye. Lateral section of anterior oculoscapular canal with anterior pore F and terminal pore H'. Posterior oculoscapular canal with two terminal pores K' and L'. Gap between anterior and posterior oculoscapular canals much shorter than length of posterior oculoscapular canal. Preopercular canal present, with three pores M', N, and O'. Sensory-papillae row “a” oblique and uniserial, composed of loosely-arranged papillae, extending anteriorly to a vertical through anterior margin of eye. Row “b” longitudinal, composed of loosely-arranged papillae, extending anteriorly to a vertical through pupil; its length longer than eye diameter. Row “c” composed of loosely-arranged papillae, extending posteriorly to a vertical through midpoint of row “b”. Row “d” composed of densely-arranged papillae, extending posteriorly to a vertical through posterior margin of pupil. Row “cp” comprising a single papilla. Row “f” comprising paired papillae. Anterior end of row oi slightly separated from a vertical row “ot”.

Coloration of males when alive [ Fig. 5A ; Suzuki et al., 2004: 450 (upper figure) and 451 (upper figure)]. Ground color of head and body baby blue. Posterior part of cheek and operculum grayish; cheek and lower half of operculum with many small bright orange dots. Snout with a broad oblique deep-orange stripe between eye and anterior one fourth of upper lip; A large triangular pale-yellow area on anterior part of cheek and lateral side of snout. Several irregular-shaped, deep or dull-orange short stripes and botches on dorsal surface of snout and interorbital space, occipital region and nape; dorsal margin of cheek edged by a narrow deep orange line and bluish green line; upper part of operculum with two oblique dull orange stripes. Temporal region with two dull orange stripes, reaching posteriorly to, or around, a vertical through origin of second dorsal fin. Many of scale pockets on body with dull orange spots. Membranes of vertical fins similar to body in coloration, with black or gray spines/rays; distal margins of vertical fins pale yellow. Caudal fin becoming blackened distally, with a narrow pale-yellow edge; central part of caudal fin with four vertical rows of bright orange dots. Pectoral fin hyaline; central part with two vertical rows of bright orange dots; base of pectoral fin with a distinct dull orange oval spot.

Coloration of female when alive [ Fig. 5B ; Suzuki et al., 2004: 450 (lower figure)]. Resembles that of male, except as follows. Orange spots on cheek and operculum indistinct, fewer in number. Paler area on anterior part of cheek and lateral side of snout very indistinct. Stripes and blotches on head and body darker. Scale pockets with indistinct pale spots. Dorsum of body with four saddle-like, large black blotches; anteriormost one at base of first dorsal fin, middle one at base of second dorsal fin, and the other two on caudal peduncle. A longitudinal series of seven large black rectangular blotches on midlateral body; first and second one ventral to first dorsal fin; third one ventral to between dorsal fins, fourth and fifth one ventral to second dorsal fin; sixth and seventh one at caudal peduncle. A pair of vertically-arranged, rounded black blotches at base of caudal fin. Caudal fin without barred pattern.

Coloration when freshly collected. Freshly-collected coloration of males ( Figs. 1 , 6A ) resembles that when alive in underwater photograph, except as follows. Ground color of head and body light or medium gray; head bluish. Ventral side of belly pale white. Branchiostegal membrane pale yellow, with many small bright orange spots. Dorsal and anal-fin membranes yellowish or bluish gray; caudal-fin membrane deep orange; distal margins of vertical fins white. Pectoral and pelvic fins similar to, or slightly more darkened than, body in coloration. Freshly-collected coloration of female ( Figs. 2 , 6B ) resembles that of males, except as follows. Ground color of head and body light bluish gray or yellow gray. Scale pockets with orange spots, forming a network pattern. Fin membranes light or bluish gray. A pair of vertically-arranged rectangular black blotches at base of caudal fin. Caudal fin without barred pattern.

Coloration when preserved in alcohol. All blue, green, orange and yellow color faded; ground color of head and body turns to reddish gray and yellowish gray in males and females respectively; blackish markings on body turn to brown.

Habitat and Distribution. Known from upper reaches of swift freshwater streams in montane areas of Ishigaki-jima and Iriomote-jima islands, Yaeyama Group of the Ryukyu Islands, Japan ( Suzuki et al, 2004). It is commonly seen in Iriomote-jima Island, whereas rare in Ishigaki-jima Island. Although a landlocked population is found in O’omija-gawa River of Iriomote-jima Island ( T. Tunagawa, personal communication), the species appears to be an amphidromous species, judging from small-sized eggs laid by the females at spawning grounds in Urauchi-gawa River, Iriomote-jima Island (Y. Yamasaki, personal communication).

Etymology. The specific name, yaima, refers to the Yaeyama Islands , the type locality of this species.

Figures

Fig. 1. Holotype of Rhinogobius yaima (KPM-NI 52486, male, 60.0 mm SL) collected from Nakara-gawa River, Iriomote-jima Island, the Ryukyu Islands, Japan.A and B: freshly-collected condition; C: alcohol-preserved condition.Photographed by T. Suzuki.

Fig. 2. Female paratype of Rhinogobius yaima (KPM-NI 53487, 51.1 mm SL) collected from O'omija-gawa River, Iriomote-jima Island, the Ryukyu Islands, Japan.A and B: freshly-collected condition; C: alcohol-preserved condition.Photographed by T. Suzuki

Fig. 3. Ventral view of pelvic fin (A), dorsal view of head (B) and ventral view of belly (C) in Rhinogobius yaima (OMNH-P 43686, paratype, male, 60.6 mm SL), stained with Alizarin Red S. White line indicates the most proximal segment of all branches in the fifth segmented ray. Black wedge indicates slits between branches. Black circles with black letters H', K', and L' indicate sensorycanal pores. Letters P1, P2, and P3 indicate anteriormost point of anterior extension of scaly area along predorsal midline, anteriormost point of anterior extensions of scaly area on temporal region, and most concaved point of scaly area between P1 and P2, respectively. Photographed and annotated by T. Suzuki.

Fig. 4. Dorsal (top), lateral (middle), and ventral (bottom) views of head of Rhinogobius yaima (KPM-NI 53486, holotype, male, 60.0 mm SL), showing cephalic sensory pores and papillae. Red circles with red letters indicate sensory canal pores (letters with prime marks indicate terminal openings of sensory canals); rows of yellow dots indicated by yellow letters represent sensory papillae rows; black arrows show ventralmost positions of gill opening. Abbreviations: AN, anterior narial pore; PN, posterior narial pore. Photographed and annotated by T. Suzuki.

Fig. 5. Underwater photographs of Rhinogobius yaima taking at Iriomote-jima Island, the Ryukyu Islands, Japan. A: male (photographed by M. Kasai); B: female (M. Suzuki).

Fig. 6. Dorsal (top), lateral (middle), and ventral (bottom) views of head in Rhinogobius yaima showing freshly-collected coloration.A: SPMN-PI 45461, paratype, male, 62.9 mm SL; B: SPMN-PI 45462, paratype, female, 45.7 mm SL. Photographed by T. Suzuki.