Rhinogobius tyoni, SUƶU & Kƚ, 2019

SUƶU, Toshiyuki & Kƚ, Seishi, 2019, Two New Lentic, Dwarf Species of Rhinogobius Gill, 1859 (Gobiidae) from Japan, Bulletin of the Kanagawa Prefectural Museum (Natural Science) 48, pp. 21-36 : 23-28

Rhinogobius tyoni sp. nov.

(Standard Japanese name: Shimahire-yoshinobori)

( Table 1 ; Figs. 1–3 )

Rhinogobius sp. OR morphotype “ Shimahire ”: Suzuki, 1996: 1 (Okayama, Hyogo and Tokushima prefectures, Japan); Akihito et al., 2002: 1254 (localities not detailed).

Rhinogobius sp. BF: Suzuki et al., 2010: 3 (Hiroshima, Okayama, Hyogo, Osaka, Nara, Wakayama, Ehime, Kagawa and Tokushima prefectures, Japan); Suzuki & Mukai, 2010: 177 (Fukuoka, Hirosima, Okayama, Hyogo, Osaka, Nara, Wakayama, Ehime, Kagawa, Tokushima, Mie, Gifu, Aichi and Shizuoka prefectures, Japan); Akihito et al., 2013: 1460 (Hiroshima, Okayama, Hyogo, Osaka, Nara, Wakayama, Ehime, Kagawa, Tokushima, Mie, Gifu and Shizuoka prefectures, Japan).

Holotype. OMNH-P 5882 , male, 37.0 mm SL, Maruyama-gawa River , Nakanogo, Toyooka, Hyogo Prefecture, Japan, 35°29'34.1"N 134°48'38.8"E, 18 March 1995.

Paratypes. Total 13 specimens (five males and eight females), 25.7–40.0 mm SL. OMNH-P 5883 , female, 27.9 mm SL, collected with the holotype ; OMNH-P 5890–5892 , 8033–8037 (including 8035 and 8036, cleared and stained), three males and five females, 25.7–37.4 mm SL, 24 March 1995 , same locality as the holotype; KPM-NI 49568 (formerly OMNH-P 35396 ) (cleared and stained) and 49569 (formerly OMNH-P 35397 ), two males, 34.7 and 40.0 mm SL, Yamamoto , Takarazuka, Hyogo Prefecture, Japan, 34°49'11.9"N 135°22'49.1"E, 13 September 2009 ; KPM-NI 49570 (formerly OMNH-P 36482 ) and 49571 (formerly OMNH-P 36483 ), two females, 29.0 and 32.8 mm SL, Ibo-gawa River , Yamasaki, Shisou, Hyogo Prefecture, Japan, 35°03'40.5"N 134°34'21.7"E, 29 June 2010 .

Diagnosis. Rhinogobius tyoni is distinguished from all congeneric species by the following combination of features: scales on predorsal area small cycloid, 8–17 scales on predorsal midline; 20–23 pectoral-fin rays; 28–35 longitudinal scales; 10+16=26 vertebrae; a low first dorsal fin in males, not extending posteriorly to origin of second dorsal fin when adpressed; third spine of first dorsal fin longest; posterior oculoscapular canal usually absent; preopercular canal usually present with two terminal pores; sensory-papillae rows on cheek arranged longitudinally, with no transverse rows; anteriorpart of first dorsal fin with no dark large circle or quadrangle dusky markings (spots or blotches); no yellow or orange markings on caudal-fin base when alive or freshly-collected; caudal fin with some dark vertical lines in males, some dark vertical lines or rows of dots in females; lower half of caudal fin reddish orange in males when alive or freshly-collected.

Description. Dorsal-fin rays VI-I, 8* (12) or VII-I, 8 (2); anal-fin rays I, 8* (10) or I, 9 (4); pectoral-fin rays 20* (4), 21 (7), or 22 (3); pelvic-fin rays I, 5* (14); segmented caudal-fin rays 9+8* (12); branched caudal-fin rays 7+6 (1), 7+7* (11), 8+7 (1), or 9+7 (1); longitudinal scales 32 (2), 33 (7), 34* (4), or 35 (1); transverse scales 9 (3), 10 (5), 11* (4), or 12 (2); scales between origin of dorsal fin and dorsal insertion of pectoral fin 7* (4), 8 (5), or 9 (2); predorsal scales 8 (2), 10 (1), 12 (1), 14 (1), 15(2), 16* (2), or 17 (2); P-V 3/12210/9* (4), 3/12211/9 (2), 3/22110/9 (6), or 3/21210/9 (1); vertebrae 10+16=26* (13) or 10+17=27 (1).

Proportional measurements based on holotype and three paratypes ( OMNH-P 5883, 5890, 5891) are given in Table 1 . Body relatively short and small (reaching up to 40 mm SL), slightly compressed anteriorly, compressed posteriorly. Head large, slightly depressed. Snout short and round. Eye large, located dorsolaterally on head at, or slightly before, a vertical through midpoint between snout tip and posterior margin of preopercle. Cheek somewhat fleshy. Lips thick and fleshy; lower lip slightly protruding beyond upper lip; gape oblique, forming an angle of about 20–30 (30 in holotype) and 40 degrees with body axis in males and females; posterior margin of lower jaw not or barely reaching to, or extending a little beyond, a vertical through anterior margin of eye. Anterior naris a short tube without skin flap at its tip, located at, or slightly before, midpoint between snout tip and anterior margin of eye; posterior naris a round pore with low rim, closer to eye than to anterior naris. 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 or half oval in males, trapezoid or semicircular in females; third spine longest; all dorsal-fin spines slender and flexible, not filamentous; when adpressed, posterior end (distal tip of third spine) of first dorsal fin usually not extending to origin of second dorsal fin. Second dorsal fin separated from first dorsal fin; second dorsal fin subequal to first dorsal fin in height in males, whereas subequal or slightly higher in females; all segmented dorsal-fin rays branched; seventh branched rays longest in males, whereas second or third ray longest in females; when adpressed, posterior end of second dorsal fin not extending to procurrent-rays part of caudal fin; posterior end of base of second dorsal fin above posterior end of anal-fin base. Origin of anal fin below base of first or second (second in holotype) branched ray of second dorsal fin; anal fin slightly lower than second dorsal fin in height; all segmented anal-fin rays branched; seventh branched ray longest in males, whereas fourth or fifth ray longest in females; when adpressed, posterior end of anal fin not extending to procurrent-rays part of caudal fin. Caudal fin nearly rounded. Pectoral fin oval; pectoral fin extending posteriorly to vertical lines between origin and base of second branched ray (base of first branched ray in holotype) of second dorsal fin in males, whereas base of sixth spine and posterior end of base of first dorsal fin in females; pectoral-fin rays branched, except for dorsalmost and/or ventralmost rays unbranched in some specimens (only ventralmost rays unbranched in holotype). Pelvic fins fused medially by well-developed frenum (between spines) and connecting membrane (between innermost rays), forming a longitudinally elongate, oval cup-like disc; pelvic fins extending posteriorly to a vertical through fifth or sixth spine base of first dorsal fin (fifth in holotype), and not reaching to anus; pelvic-fin spine with triangular membranous lobe at its tip; all pelvic-fin segmented rays branched; first branched ray longer than spine; first branch of fifth pelvic-fin ray bifid ( Fig. 1A ).

Scales on body small ctenoid anteriorly, moderately large ctenoid posteriorly. Scaly area on body extending posteriorly to base of caudal fin; basal part of caudal fin with small cycloid scales. Anterodorsal part of body before a diagonal line from origin of first dorsal fin to dorsal insertion of pectoral fin with small scales. Anterior part of predorsal area naked. Predorsal squamation with trifurcate anterior edge, anterior extensions of middle and both sides extending anteriorly beyond a transverse line through dorsalmost point of pectoral-fin axil to beyond above canal pore H' ( Fig. 1B ). The other part of head naked. Lateral and ventral sides of belly with ctenoid scales and small cycloid scales, respectively. Pelvic-fin axil naked. Scaly area of belly not extending anteriorly to pelvic-fin insertion. Base of pectoral fin and prepelvic areas with 0–4 and 0–17 (0–7 in preventral midline) small cycloid embedded scales, respectively.

Cephalic sensory systems of holotype ( OMNH-P 5882 ) are illustrated in Suzuki (1996: 3, fig. 1), and not repeated here. Based on our examination of ten specimens ( OMNH-P 5882 , 5883 , 5890–5892 , 8033–8037 ), considerable variations in development of sensory canals on head are found. On the anterior oculoscapular canal, eight specimens including holotype have a nasal extension with terminal pore B' located anterodorsal to posterior naris; anterior interorbital sections separated with paired pore C and a single median pore D, pore E just behind posterior edge of eye; lateral section with anterior pore F and terminal pore H'. Of the remaining two, one lacks a canal between pores F and H, and the other has only a short canal with two terminal pores B' and C'. On the posterior oculoscapular canal, nine specimens including holotype lack a posterior oculoscapular canal, whereas a single specimen has it. On the preopercular canal, three specimens have pores M', N, and O', the other four including holotype lack intermediate pore N, and a single specimen lacks the canal. The Following description of sensory papillae is based on holotype ( OMNH-P 5882 ). Sensory-papillae row a oblique and uniserial, composed of five sparsely arranged papillae, extending anteriorly slightly beyond a vertical through middle of eye. Row b longitudinal, composed of densely arranged papillae, extending anteriorly to a vertical through middle of eye; its length equal to eye diameter. Row c composed of sparsely arranged papillae, extending posteriorly slightly behind a vertical through posterior margin of eye. Row d composed of densely arranged papillae, extending posteriorly slightly behind a vertical through posterior margin of pupil. Rows cp and f comprising single and a pair of papillae, respectively. Anterior end of row oi close to a vertical row ot.

Coloration of males (see also Suzuki, 1996: 8, figs. 2, 4; Suzuki et al., 2017: 61, fig. 3). Freshly-collected coloration of male holotype ( Fig. 2A ) is as follows. Ground color of head and body yellowish gray darkened dorsally. Iris vivid yellow, margined dorsally by vivid green. Two red oblique stripes on snout; one between eye and tip of snout, the other between ventral margin of eye and posterior end of upper jaw. Cheek and lower part of operculum with several vague, irregularly-shaped yellow spots (fairly vivid in operculum). Branchiostegal membrane yellow, tinged with bright blue ventrally, without any distinct markings. Dorsal margin of lower jaw and ventral side of head bright blue. Scale pockets of nape and occipital region with dull red spots. Dorsalmost of pectoral-fin base with a triangular bright blue marking as large as (or slightly smaller than) pupil, edged ventrally by black. Each scale pockets on dorsal and midlateral parts of body with a small dull red spot. Midlateral body with a broad dull blue stripe. Belly whitish, tinged with yellow dorsally, bright blue posteriorly. Dorsal fins pale yellow gradually turns to dull purple distally, with broad pale-yellow anterodorsal margins; several dull purple dots just behind spines on ventral one-third of first dorsal fin, forming 1–2 indistinct horizontal rows; four indistinct, horizontal dull purple lines on second dorsal fin (dorsal two largely faded anteriorly). Anal fin grayish, darkened distally, with a broad midlateral orange stripe and white distal margin. Caudal fin pale, with red purple dorsal part, reddish orange lower half, and yellow posterior margin; base with a “ <”sharped grayish brown blotch, and central part with four red purple vertical lines. Pectoral and pelvic fins nearly transparent and grayish, with slightly darkened rays. When preserved in alcohol ( Fig. 2B ), all blue, green, orange, purple, red and yellow markings faded; ground color of head and body turns to yellowish white.

Coloration of females. Freshly-collected coloration of females ( Fig. 3A ; Suzuki, 1996: 8, figs. 3 and 6; Suzuki et al., 2017: 63, fig. 4B) resembles that of males, except as follows. No yellow markings on cheek, operculum and branchiostegal membrane. Midlateral body with a longitudinal series of 7–8 indistinct circular, large black blotches; anterior two below first dorsal fin, middle 3–5 below second dorsal fin, and the others on caudal peduncle. Dorsum of body with several irregular-shaped, black blotches. Posterior part of second dorsal fin with 1–4 reddish gray strips. A single narrow orange stripe at midlateral anal fin (sometimes barely visible or absent; see, e.g., fig. 5 of Suzuki, 1996). Central part of caudal fin with 1–7 reddish gray vertical lines or rows of dots; these lines/rows of dots not extending to dorsal and ventral onesixth or one-seventh of the fin. When preserved in alcohol ( Fig. 3B ), all blue, green, orange, purple, red and yellow markings faded; ground color of head and body turns to yellowish white; blackish markings on body turn to brown.

Coloration when alive (see Suzuki, 1996: 9, figs. 6, 7). Coloration when alive in aquaria resembles that of freshly-collected specimens, except as follows: midlateral body with a longitudinal series of seven large rounded black blotches: dorsum of body with six saddle-like black blotches, comprising anteriormost one on nape, middle three below dorsal fins, and posterior two on caudal peduncle.

Distribution. Rhinogobius tyoni is hitherto known from inland waters in temperate Japan along coasts of Seto Inland Sea, Osaka Bay and Kii Channel (Fukuoka, Hiroshima, Okayama, Hyogo, Osaka, Nara, Wakayama, Ehime, Kagawa and Tokushima prefectures), and Maruyama-gawa River of Hyogo Prefecture, draining to Sea of Japan. This species is also found in the Tokai District of Japan (including Mie, Gifu, Aichi and Shizuoka prefectures), but the populations seem to have been artificially introduced (Suzuki et al., 2010; Suzuki & Mukai, 2010; Akihito et al., 2013).

Habitat. Rhinogobius tyoni is found in shallow freshwater areas with mud bottoms and aquatic vegetation, such as ponds, marshes, reservoirs, canals, and creeks at middle or lower reaches of rivers (Suzuki & Mukai, 2010; present study). It is a non-diadromous species, restrictedly found in non- or barely-flowing freshwater habitats throughout the life cycle ( Ohara et al., 2009; Tsunagawa et al., 2010a; present study).

Etymology. The specific name, tyoni , refers to the late Darsu Tyon, who discovered the species and kindly informed us for our study.

Figures

Fig. 1. Ventral view of pelvic fin (A) and dorsal view of head (B) of Rhinogobius tyoni (KPM-NI 35396, paratype, male, 37.0 mm SL), stained with Alizarin Red. White line indicates the first segment of each branch in the fifth soft ray. Black arrow indicates a slit between branches. Pink dots indicate scales along edge of scaly area on nape and occipital region; P1, P2, and P3 indicate boundary of anterior extension of scaly area along predorsal midline, boundary of anterior extension of scaly area on side of occipital region, and boundary of most concave point of scaly area between P1 and P2, respectively. Photographed and annotated by T. Suzuki.

Fig. 2. Freshly-collected (A) and alcohol preserved (B) holotype of Rhinogobius tyoni (OMNH-P 5882, male, 37.0 mm SL). Photographed by T. Suzuki.

Fig. 3. Freshly-collected (A) and alcohol preserved (B) paratype of Rhinogobius tyoni (OMNH-P 5883, female, 27.9 mm SL). Photographed by T.Suzuki.