Navigobius asayake, Okamoto & Motomura, 2018

Okamoto, Makoto & Motomura, Hiroyuki, 2018, Navigobius asayake, a new species of ptereleotrine goby (Gobioidei: Microdesmidae) from Kagoshima, southern Japan, Zootaxa 4526 (3), pp. 373-380 : 374-379

Navigobius asayake new species

[New English name: Sunrise Dartfish; new standard Japanese name: Asayake-kaguya-haze]

( Figs. 1–4 ; Table 1)

Gobiidae , indet. gen. and sp.; Yamada & Ito, 1995: 1, unnumbered fig. (between Goto Islands and Tsushima island, western Japan).

Holotype. KAUM–I. 115659, female, 48.8 mm SL, off Satsuma Peninsula , Kagoshima, Japan, 150 m depth, 19 August 2016.

Paratypes. 3 specimens: KAUM–I. 115660, female, 47.8 mm SL, collected with holotype; KAUM–I. 115661, female, 45.0 mm SL, collected with holotype; KAUM–I. 83848, male, 52.1 mm SL, off Mihama , Nishinoomote , Tanegashima island, Osumi Islands, Kagoshima, Japan, 30°44′N, 130°59′E, 20 m depth, gill net, FV An-ei-maru, 29 February 2016 .

Other materials. 2 specimens: SNFR 1067 , 54.0 mm SL, SNFR 1074 , 55.1 mm SL, between Goto Islands and Tsushima Island, Nagasaki, Japan, bottom trawl .

Diagnosis. A species of Navigobius with the following combination of characters: second dorsal-fin rays I, 18–19; anal-fin rays I, 19; pectoral-fin rays 21–22; gill rakers 5–6 + 13–15; head length 25.1–26.4% SL; eye diameter 8.6–10.0% SL; pelvic-fin length 15.2–16.1% SL; and developed yellow stripe extending from behind upper part of eye to beneath first dorsal fin.

Description. Counts and measurements of holotype and paratypes are shown in Table 1. Body elongate and laterally compressed, more strongly posteriorly ( Fig. 1 ). Head large, laterally compressed, its length about 1/4 of standard length. Mouth oblique, forming angle of 40–45° to horizontal axis of body; posterior margin of maxilla not extending to below anterior margin of pupil; lower jaw slightly projecting when mouth closed; maxilla with two rows of conical teeth, outer row widely spaced, slightly curved, and enlarged compared to inner row; dentary with single row of mixed curved large and small conical teeth, except two or three pairs of curved conical teeth on each side at front corner; no teeth on vomer and palatines. Snout short and round, length shorter than bony interorbital width; nostrils set at level of upper edge of pupil, anterior nostril short tube, posterior nostril elliptical. Eye large, round, its diameter almost twice snout length; bony rim of orbit slightly raised above dorsal profile; interorbital region broad, flat. Gill opening extending from upper pectoral-fin base ventrally to below posterior margin of preopercular; shallow notch present on lower margin of gill membrane. Origin of first dorsal fin above anterior part of pectoral fin; first dorsal-fin spines not elongate, height of fin about same height as second dorsalfin; fifth dorsal-fin spine longest. Origin of anal fin below 2nd soft ray of second dorsal-fin; its posterior rays not prolonged. Pectoral fin broad, posterior margin rounded; uppermost 2 and lowermost 2 rays unbranched; posterior tip of fin just below last spine of first dorsal-fin. Pelvic fin just below pectoral-fin base; outer 1–3 soft rays branched, fourth soft ray unbranched; third ray longest, posterior end below center of between fifth and sixth dorsal-fin spines. Caudal fin forked, upper lobe longer than lower lobe, lower lobe 76–79 % length of upper lobe. Anus located slightly posterior to vertical drawn through origin of second dorsal fin. Scales mostly cycloid, covering whole body except for head, nape, all fins, and dorsal- and anal-fin bases; ctenoid scales hidden beneath depressed pectoral fin, and present on lateral side of posterior body and caudal peduncle. Cephalic sensory pores and superficial neuromasts on head as shown in Fig. 2 .

Color in fresh condition. Body and head pale pink, lower part of head and abdominal cavity silvery-white; purple stripe from behind upper part of eye to upper edge of operculum; nuchal crest reddish-pink; yellow band from snout tip to anterior margin of eye; iris yellow, blackish silver dorsally, with smaller marking ventrally; yellow spot or short band behind eye on preopercle; yellow stripe from behind upper part of eye to beneath first dorsal fin ( Fig. 1C ); dorsal fins with yellow bands, purple bar between yellow bands, distal parts of dorsal fins purple; anal fin with two yellow bands, purple bar between yellow bands; pectoral fin and its base pale pink; pelvic fin silvery white; caudal fin red-purple, upper lobe of caudal fin with yellow margin, lower margin of lower lobe of caudal fin yellow.

Color in alcohol. Head and body uniformly light brown; fins translucent; scattered melanophores on lateral side of body and caudal-fin base.

Distribution. Collected off the Satsuma Peninsula and Tanegashima Island, Kagoshima, Japan ( Fig. 3 ), in depths of 20– 150 m. In addition, this species was reported from between the Goto Islands and Tsushima Island, western Japan, at a depth of 115–116 m ( Yamada & Ito 1995).

Etymology. The specific name “ asayake ” is from a Japanese noun, which means “sunrise colors”, in reference to the reddish coloration of the species ( Fig. 1 ).

Comparisons. Navigobius asayake is most similar to N. dewa , but differs in having a higher pectoral-fin ray count (21–22 vs. 20 in the latter), larger head (head length 25.1–26.4% SL vs. 23.7–24.3% SL) and larger eye (eye diameter 8.6–10.0% SL vs. 7.7–9.4% SL), and a shorter pelvic fin (pelvic fin length 15.2–16.1% SL vs. 18.7– 19.4% SL). The number of the second dorsal-fin soft rays of three type specimens of N. asayake are 18, while all type specimens of N. dewa have 19 ( Hoese & Motomura 2009). This suggests that the number of the second dorsalfin soft rays differs modally between N. asayake and N. dewa .

Navigobius asayake is easily distinguished from other two congeners N. kaguya and N. vittatus by having 18– 19 second dorsal-fin soft rays (vs. 16 in N. kaguya and 11–13 in N. vittatus ) and 19 anal-fin soft rays (vs. 16 in N. kaguya and 10–12 in N. vittatus ). In addition to the meristic characters, N. asayake differs from N. kaguya and N. vittatus in having a well-developed yellow stripe extending from behind the upper part of the eye to beneath the first dorsal fin (vs. a weak or absent stripe extending to the opercular margin in N. kaguya or a well-developed stripe extending to above the pectoral-fin base in N. vittatus ). Gill et al. (2017) also reported an undescribed species of Navigobius as N. cf. kaguya from the Maldives and Bali in the original description of N. kaguya ; however, it has 16 soft rays in the second dorsal and anal fins.

Remarks. Yamada & Ito (1995) showed a color photograph of an unidentified gobiid fish collected from between the Goto Islands and Tsushima Island, western Japan, at a depth of 115–116 m and commented on the morphological features of two specimens. According to their report, the specimens possess VI-I, 18 dorsal-fin rays, I, 19–20 anal-fin rays, 21 pectoral-fin rays, and 5 + 1 + 13–14 gill rakers. These meristics provided by Yamada & Ito (1995) and coloration of the photographed specimen agree well with N. asayake , suggesting that N. asayake is widely distributed on the continental shelf in the East China Sea.

In their description of N. dewa, Hoese & Motomura (2009) provided morphometric data from only the holotype. Morphometric data from two paratypes of N. dewa re-examined in this study are provided in Table 2.

Comparative material. Navigobius dewa : KAUM–I. 5516, 40.7 mm SL, KAUM–I. 5517, 45.2 mm SL, 2 paratypes, off Sakurajima , Kagoshima Bay, Kagoshima Prefecture, Japan, 25 July 2007 .

Figures

FIGURE 1. Navigobius asayake n. sp.. (A) KAUM–I. 115659, holotype, 48.8 mm SL; (B) lateral view of KAUM–I. 83848, paratype, 52.1 mm SL; (C) dorsal view of KAUM–I. 83848, paratype, 52.1 mm SL.

FIGURE 2. Laterosensory pores and neuromasts of Navigobius asayake n. sp., KAUM–I. 115660, 47.8 mm SL. Arrow indicates lower attachment of gill membrane.

FIGURE 3. Collection localities of Navigobius asayake n. sp. Closed stars and open star indicate specimens examined in this study and Yamada & Ito (1995), respectively.

FIGURE 4. Lateral view of heads of two Navigobius species. (A) Navigobius asayake, KAUM–I. 115661, paratype, 45.0 mm SL; (B) N. dewa, KAUM–I. 5517, paratype, 45.2 mm SL.