Rhinogobius aonumai ishigakiensis, Suzuki & Oseko & Yamasaki & Kimura & Shibukawa, 2022

Suzuki, Toshiyuki, Oseko, Naoharu, Yamasaki, Yo Y., Kimura, Seishi & Shibukawa, Koichi, 2022, A New Species with Two New Subspecies of Rhinogobius (Teleostei: Gobiidae) from Yaeyama Group, the Ryukyu Islands, Japan, Bulletin of the Kanagawa Prefectural Museum (Natural Science) 51, pp. 9-34 : 22-28

Rhinogobius aonumai ishigakiensis subsp. nov.

(New Standard Japanese name: Ishigaki-painukibara-yoshinobori)

( Figs 9–15 & 17B; Tables 2 & 3)

Rhinogobius brunneus (not of Temminck & Schlegel): Hayashi, 1984: 259 (in part: Medium Egg Type, Ishigaki-jima Island , the Yaeyama Group of the Ryukyu Islands, Japan) .

Rhinogobius sp. YB: Iwata, 1989: 598 (in part: Ishigaki-jima Island); Akihito et al., 1993: 1082 (in part: Ishigaki-jima Island); Akihito et al., 2000: 1255 (in part: Ishigaki-jima Island); Akihito et al., 2002: 1255 (in part: Ishigaki-jima Island); Suzuki et al., 2004: 460 (in part: Ishigaki-jima Island); Akihito et al., 2013: 1461 (in part: Ishigaki-jima Island); Suzuki et al., 2021: 466 (in part: Ishigaki-jima Island).

Holotype. SPMN-PI 49269 , male, 51.5 mm SL, Sakuta-gawa River , Ishigaki-jima Island , the Yaeyama Group of the Ryukyu Islands, Japan, upper reaches above some falls (total vertical height about 100 m), 165 m above sea level, 26 Oct. 2020, Fig. 9.

Paratypes. Total 11 specimens (6 males and 5 females, 33.3–56.5 mm SL), collected from Ishigaki-jima Island. Miyara-gawa River : OMNH-P 40912 ( Fig. 14A) and 40914 ( Fig. 14B), male and female, 38.0 and 38.4 mm SL, upper stream above Maezato Dam, 93 m above sea level, 19 June 2014 ; Sakuta-gawa River : OMNH-P 48920 , 48922 , 48923 and 48924, three males and female, 38.0, 37.2, 35.5 and 35.5 mm SL, stained with Alizarin Red S., the same locality as holotype, 18 Sep 2020 , KPM-NI 65589 and 65588 ( Fig. 14C), female and male, 56.5 and 55.9 mm SL, female is stained with Alizarin Red S., the same locality as holotype, 19 Oct. 2020 , SPMN-PI 49270 ( Figs. 10, 14D), female, 45.0 mm SL, collected with the holotype ; Sokobaru-gawa River , a tributary of the Miyara-gawa River System: OMNH-P 40911 ( Fig. 14E) and 40913 ( Fig. 14F), male and female, 39.9 and 33.3 mm SL, upper stream above Sokobaru Dam, 159.6 m above sea level, 22 June 2014 .

Photograph Records from Image Database of Fishes. Ayamashi-gawa River , a tributary of the Miyara-gawa River System : KPM-NR 217906, male, about 40 mm SL, 24°23′47.59″N 124°11′07.28″E, 34 m above sea level, 17 September 2021, Naoharu Oseko; Isobe-gawa River : KPM-NR 217904 and 217905, male and female, about 35 mm SL, upper stream above Ishigaki Dam, 24°22′28.39″N 124°09′59.25″E, 113 m above sea level, 17 September 2021, Naoharu Oseko; Pensann-kara River , a tributary of the Uratabaru-gawa River System : KPM-NR 217910 and 217911, male and female, about 40 and 35 mm SL, 24°22′37.00″N 124°09′39.45″E, 90 m above sea level, 7 March 2018, Naoharu Oseko; Todoroki-gawa River: KPM-NR 217907 and 217908, male and female, about 35 mm SL, 24°23′52.60″N 124°13′36.59″E, 25 m above sea level, 10 March 2021, Naoharu Oseko; A tributary of the Todoroki-gawa River: KPM-NR 217909, male, about 35 mm SL, 24°23′37.23″N 124°13′04.84″E, 25 m above sea level, 10 March 2021, Naoharu Oseko .

Diagnosis. Rhinogobius aonumai ishigakiensis is distinguished from all congeneric species-group taxa by having the following combination of features: 10–14 predorsal scales; 33–38 longitudinal scales; 10+16–18=26– 28 vertebrae (mode 27); anteriormost two pterygiophores (proximal radials) of second dorsal fin mounted over neural spine of nineth vertebra; fifth segmented pelvic-fin ray divided into 2–3 (usually two) branches at the position where proximal most segment of each branch alignes transversely; sensory-papillae rows on cheek arranged longitudinally, with no transverse rows; yellow-colored body in freshly-collected; no dark spot on first dorsal fin; caudal fin with 7–9 and 3–6 dark zigzag bands in males and females, respectively; a pair of short, vertically aligned, rod-shaped dark mark on caudal-fin base in females.

Description. First dorsal-fin rays V (1) or VI * (11); second dorsal-fin rays I, 8* (9) or I, 9 (3); anal-fin rays I, 7 (2), I, 8* (2) or I, 9 (8); pectoral-fin rays (left/right) 18/18 (1), 18/19 (1), 19/18 (1), 19/19 (4), 19/20 (3), 20/19* (1) or 20/20 (1); pelvic-fin rays I, 5 (12); segmented caudal-fin rays (upper part + lower part) 9+8* (10) or 9+9 (2); branched caudal-fin rays (upper part + lower part) 7+7 (6), 8+7* (5) or 9+7 (1); longitudinal scales 33 (2), 34 (1), 35 (6), 36 (1), 37* (1) or 38 (1); transverse scales 9 (7) or 10*(5); scales between origin of dorsal fin and dorsal insertion of pectoral fin 8 (5) or 9* (7); predorsal scales 10 (1), 11 (4), 12 (2) or 14* (5); number of the first branches of fifth segmented pelvic-fin ray (left/right) at the position where proximal most segment of each branch alignes transversely ( Fig. 11A) 2/2* (10), 2/3 (1) or 3/2 (1); P-V 3/21210/9 (1), 3/22100/9 (1), 3/22110/9 (9) or 3/22200/9* (1); vertebrae (abdominal + caudal = total vertebrae) 10+16=26 (3), 10+17=27 (7) or 10+18=28* (2).

Head slightly large and slightly depressed; body slightly slender, slightly compressed anteriorly, and compressed posteriorly. Snout nearly pointed, long, and longer than eye diameter; snout length of males greater than that of females. Eye large, dorsolateral on head, and located slightly behind a vertical through midpoint between snout tip and posterior margin of preopercle. Cheek somewhat bulbous and fleshy. Lips thick and fleshy; anterior tips of both lips even* or lower lip slightly protruding anteriorly; gape slightly oblique; posterior margin of lower jaw extending posteriorly to a vertical through anterior margin of eye in females and slightly beyond it in males. Anterior naris a short tube without skin flap at its tip, and its base located slightly behind the midpoint between snout tip and anterior margin of eye. Posterior naris a round pore with low rim and located the midpoint between base of anterior naris and anterior margin of eye. Gill opening usually extending anteriorly to center of operculum*, or 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 about an eye diameter behind a vertical through dorsal insertion of pectoral-fin; first dorsal fin in males usually near falcate shape, and higher than second dorsal fin in height, whereas, in females, semicircular or semioval, and usually slightly higher than, or slightly lower than second dorsal fin in height; usually second, or third* spine longest; all dorsal-fin spines slender and flexible; distal tip of first dorsal fin in males usually second or third* spine filamentous, or with non-filamentous spines, whereas, in females with non-filamentous spines; posterior tip (= distal tip of second or third* spines) of first dorsal fin in males extending between bases of first and fifth segmented ray of second dorsal fin (forth ray*) when adpressed, whereas, in females, posterior tip (= distal tip of third, fourth or sixth spine) usually not, or extending to origin of second dorsal fin, when adpressed. First and second dorsal fins not connected by membrane; all segmented rays of second dorsal fin branched; seventh or eighth* and second or third segmented rays longest in males and females, respectively; posterior tip (= distal tip of last or penultimate* segmented ray) of second dorsal fin not extending to caudal fin when adpressed; posterior end of second dorsal-fin base above posterior end of anal-fin base. Origin of anal fin below between origin and base of second segmented ray of second dorsal fin (between bases of first and second segmented rays*); anal fin slightly lower than second dorsal fin in height; all segmented anal-fin rays branched; sixth or seventh*, and fourth or sixth segmented rays longest in males and females, respectively; posterior tip (= distal tip of last or penultimate* segmented ray) of anal fin not extending to caudal fin when adpressed. Pectoral fin oval, extending posteriorly to a vertical between base of sixth spine of first dorsal fin and origin of second dorsal fin (posterior end of first dorsal-fin base*); pectoral-fin rays branched, except for dorsalmost and ventralmost rays unbranched. Pelvic fins fused medially by well-developed frenum (between spines) and connecting membrane (between innermost rays), forming a circular cup-like disc; pelvic fins extending posteriorly to a vertical between bases of second and fifth* spines of first dorsal fin, not reaching to anus; pelvic-fin spine with a rounded membranous lobe at its tip; all segmented rays of pelvic fin branched. Caudal fin elliptical or fan-shaped*.

Scales on body largely ctenoid, becoming smaller anteriorly; anterior edge of scaled areas with ctenoid scales on lateral, dorsal and ventral sides of body reaching respectively to a little behind pectoral-fin axilla, to between end of first dorsal fin and end of second dorsal fin, and to anal-fin base ( Fig. 12A). Small cycloid scales on anterodorsal part of body before the area with ctenoid scales. Predorsal squamation with trifurcate anterior edge; its mid-anterior extension ( Fig. 11B: P1) extending anteriorly to between transverse lines through sensory-canal pore H′ and K′; anterior extensions of lateral sides ( Fig. 11B: P2) extending anteriorly to posterior oculoscapular canal; greatest concaved point of anterior margin of scaled area of predorsal region between P1 and P2 ( Fig. 11B: P3) extending posteriorly to above between sensory-canal pore K′ and upper end of pectoral-fin axilla. Pectoral-fin base usually naked, or with one small cycloid scale. Prepelvic area usually naked, or with some small cycloid scales. Scaled area on belly with small cycloid scales usually extending anteriorly to, or not side of prepelvic area; belly above pelvic fin naked, and its following ventral midline of belly usually with small cycloid scale, or its anterior part naked ( Fig. 12B).

Cephalic sensory systems are illustrated in Fig. 13. Nasal extension of anterior oculoscapular canal with terminal pore B′ located above between both nares. 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 narrower than length of posterior oculoscapular canal. Preopercular canal present, with three pores M′, N, and O′. As unusual variations, there is an accessory pore on the canal between pores F and H′ in a paratype, and pore N is absent in two paratypes. Sensory-papillae row “a” oblique and uniserial, composed of loosely-arranged papillae, and extending anteriorly to a vertical through midpoint between anterior margin of eye and anterior margin of pupil. Row “b” longitudinal, composed of densely-arranged papillae, extending anteriorly to a vertical through center of pupil, and equal to eye diameter in length. Row “c” composed of loosely-arranged papillae, extending posteriorly to a vertical through posterior margin of eye. Row “d” composed of densely-arranged papillae, extending posteriorly to a vertical through midpoint of pupil. Row “cp” comprising a single papilla. Row “f” comprising paired papillae. Anterior end of row “oi” a little separated from a vertical row “ot”.

Coloration of male when freshly collected ( Figs. 9A, 9B, 14A, 14C, 14E, 14G). Ground color of head and body usually reddish yellow. Belly pale yellow and its side greenish. Head grayish; cheek, lower half of operculum and gill membrane with sparsely-arranged, some small purplish red dots. Snout with a broad oblique purplish red stripe between anterior margin of the eye and anteriormost part of snout. Several irregular-shaped, short purplish red stripes and minute spots on dorsal surface of snout and interorbital space, occipital region and nape; anterodorsal margin of cheek with a narrow purplish red line edged ventrally by a bright blue line; temporal region above operculum with a short purplish red stripe; upper part of operculum with two oblique purplish red stripes. Almost all scale pockets on body with reddish orange spots. Lateral side of body below dorsal-fin base with two longitudinal rows of blue spots. Ground color of fin membranes yellowish gray, partially with bluish sheen. Spines and segmented rays gray. Anterodorsal part of first dorsal fin and distal margin of second dorsal fin pale yellow; distal margin of anal fin white; dorsal and middle margins of caudal fin pale yellow and ventral margin white; membranes around spines and segmented rays of first dorsal and anal fins, and upper and lower parts of caudal fin purplish red. Second dorsal fin with three longitudinal rows of reddish orange* or purplish red spots, or usually forming zigzag stripes; a reddish orange or purplish red* mottles above these spots or stripes. Central part of caudal fin with 7–9 (8*) reddish orange or purplish red* zigzag bands. Upper end of pectoral-fin base with a black triangle mark; pectoral-fin base with a reddish orange* or purplish red bow-shaped mark, and in some specimens (except holotype), a vertical row of spots behind it.

Coloration of female when freshly collected ( Figs. 10A, 10B, 14B, 14D, 14F). Resembles that of male, except as follows. Red or orange marks of head and body darker. Purplish red dots on cheek and operculum fewer in number, usually absent on operculum; gill membrane with no orange dots. Ventral side of body usually with no reddish orange spots. Second dorsal fin with 0–4 longitudinal rows of purplish orange spots or forming zigzag stripes. Caudal-fin base with a pair of short, vertically aligned, rod-shaped grayish brown mark; central part of caudal fin with 3–6 indistinct purplish red zigzag bands. Pectoral-fin base with no vertical rows of spots behind a bow-shaped mark.

Coloration when alive based on underwater photographs ( Fig. 15). Coloration when alive in the populations of Sakuta-gawa River, in Ishigaki-jima Island resembles that of freshly-collected coloration, except as follows. Ground color of head and body grayish; upper half of body with some pale blue spots; caudal-fin base with a Y-shaped, reddish gray mark in male.

Coloration when preserved in alcohol ( Figs. 9C, 10C). Ground color of head and body turned to light gray; blue, green, yellow and white color faded; orange and red color turns to brown or gray. Dorsal side of body with 1–2 longitudinal row(s) of dark gray spots; mid lateral side of trunk with a brownish gray broad stripe in female.

Distribution and habitat. Rhinogobius aonumai ishigakiensis is known only from Ishigaki-jima Island, the Yaeyama Group of the Ryukyu Islands, Japan. In this island, it is seen in the upper reaches of freshwater streams above waterfalls in montane areas of Sakuta-gawa River, and the upper streams above Maezato Dam of Miyara-gawa River and Sokobaru Dam of Sokobaru-gawa River of Miyara-gawa River System. In addition, we identified the gobies in the photographs taken from Isobe-gawa, Todoroki-gawa and Uratabaru-gawa rivers registered in the Image Database of Fishes, as R. a. ishigakiensis. The subspecies is usually found in small pools of streams, called “Fuchi” in Japanese.

Etymology. The subspecific name, ishigakiensis, refers to the type locality (Ishigaki-jima Island, the Yaeyama Group of the Ryukyu Islands, Japan).