Ophiocara gracilis Tanaka, 1909

Ophiocara gracilis Tanaka, 1909

Material examined: Syntypes: BMNH 1894.6.30.172- 177, three males and three females (34–50 mm SL); Palawan Island , Philippines .

Others: SMF 19750 About SMF , one female (55 mm SL); Sumi Yashi , Okinawa, Japan; 20 Aug. 1978; Abe coll. BLIP 11910134 , two males (57–62 mm SL); Yufujima , Okinawa, Japan, 27 June 1991; Sakamoto, Yanohara & Kamisato coll. BLIP 19950054 , one female (76 mm SL); Amitori , Okinawa, Japan, 1 Nov. 1995; Iwata & Ikeda coll. BLIP 19890078 , one male (52 mm SL); Ohtahara , Okinawa, Japan, 21 Aug. 1989; Azawa, Senou, Suzuki, & Uryu coll. BLIP 19990308 , one male (51 mm SL); Yufujima , Okinawa, Japan, 27 June 1991; Sakamoto, Yanohara & Kamisato coll. BLIP 19990309 , one male (49 mm SL); Yufujima , Okinawa, Japan, 27 June 1991; Sakamoto, Yanohara & Kamisato coll. BLIP 19990310 , one female (51 mm SL); Yufujima , Okinawa, Japan, 27 June 1991; Sakamoto, Yanohara & Kamisato coll. BLIP 19990311 , one female (49 mm SL); Yufujima , Okinawa, Japan, 27 June 1991; Sakamoto, Yanohara & Kamisato coll. UF 182020 , one male (11.5 mm SL); Palau, 22 March 2010 ; Englund et al. coll .

Description: The ray and scale counts are given in Table 4 and selected morphometrics in Table 5. The body is compressed laterally. The body depths in males are greater than in females: at anus the body depth is 24–30% SL for females and 28–35% SL for males, at first dorsal fin 26–29% SL for females and 28–35% SL for males. The caudal peduncle depth is 14–17% SL. This species is one with the highest body depth in the male, whatever the age or size. Pre-dorsal length 40–46% SL and preanal length 59–64% SL. Size: up to 7.5 cm SL.

The head is 29–33% SL, rounded dorsally with a broad interorbital, the snout is pointed. The mouth (terminal) and jaw length 8–9% SL are small; jaws oblique with several rows of conical teeth, 8–14 on first upper outer raw (the biggest in front are usually curved), 5–8 on the first lower outer raw. Posterior end of maxillary ending below posterior nostril before eye. Anterior nostril at the end of a short tube above upper lip; posterior nostril a simple pore in front of eye. Eye diameter 6–9% SL and interorbital length 8–10% SL.

Dorsal fins mostly VI –I,8 with no filamentous rays. The first dorsal fin is with second, third, fourth and fifth rays longer. Anal fin mostly I,10 directly opposite to the second dorsal fin. The caudal fin is with 11 branched rays and its posterior margin is straight or slightly rounded. Pelvic fins separate, I,5. Pectoral fins 14–15. Lateral scales 26–27 with ctenoid scales on flanks and caudal peduncle. Pre-dorsal scales cycloid anteriorly from snout, adjacent to anterior nostril, to D1. Ctenoid scales on operculum, on base of pectoral fins and on belly extending to anus. Cheek with 2–3 rows of cycloid and ctenoid scales. Scales in transverse back series 8–9, in transverse forward 9–11, in pre-dorsal 15–17 and in zigzag 6–7, interorbital scales 2–3. Vertebrae 25. Gill opening extending to below posterior preopercular margin.

Males have a more elongated second dorsal fin (28– 37 vs. 21–28% SL) and anal fin (35–39 vs. 26–29% SL) than females and a higher first dorsal fin.

Males with a slightly triangular urogenital papilla with a small angular lateral extension on each side on the distal part. The females have rectangular or chalice-shaped bulbous urogenital papilla with crenulated outer edges around the distal opening.

Cephalic sensory pore system as described by Akihito et al. (1988) with oculoscapular canal nasal to post-temporal with the pores C’, D, E’, K’, L’; preopercular canal long with the pores M’, N, O, P’.

Colour in preservation: Male and female usually similar except for fins. Background of body brown on the back and on the flanks; belly clear brown. A faint dark blotch on dorsal half of pectoral fin base and lower half of caudal fin base. Top and middle of head brown, inferior part clear brown. A slight longitudinal black band in male, distinct stripe in female. Males ( Fig. 6C): First dorsal fin generally greyish with a basal white band, and another one at the tip. Second dorsal fin with several (3–4) rows of ovoid white spots. Anal and caudal fins hyaline. Females: Fins hyaline.

Colour in life: The coloration is somewhat variable but breeding males are often more brightly coloured than females which are usually with lighter fins and often without distinctive spots or stripes. Males ( Fig. 6A): Head and body greenish brown to yellowish, orange or yellowish on the head, greyish to black on isthmus and white ventrally on abdomen. A red-blue spot on operculum, and a dark blotch on the superior part of the pectoral fin base. No dark brown longitudinal band from posterior edge of operculum to caudal fin base and no distinct dark blotch on lower half of caudal fin base. First dorsal fin generally black with a basal white to bluish band or spots, and another one at the anterodorsal edge. Second dorsal fin with several (3–4) rows of ovoid white to bluish spots or vertical bands in the middle part, and with a white line at the dorsal edge. Anal fin mostly hyaline or red to orange. Caudal fin yellow at the base, orange, black and whitish to bluish at the tip. Pectoral fin orange at the base, black and whitish to bluish at the tip. Females ( Fig. 6B): Head and body greenish brown to yellowish, greyish on underside of head and whitish ventrally on abdomen. A faint dark brown longitudinal band from posterior edge of operculum to caudal fin base with a distinct dark blotch on lower half of caudal fin base. A golden red and blue spot on operculum. Fins hyaline. Genital papillae orange on both sexes.

Ecology: Hypseleotris everetti occurs in coastal streams from estuaries to lower parts of rivers and ponds, usually in bank vegetation. Yanagi (1977) and Dotsu et al. (1998) studied the larval development of this species from Okinawa. The females spawn a few thousand eggs (0.30~ 0.36 mm). They noted that larvae have salinity tolerance and that hatching might occur in freshwater but it is not clear whether the larvae need salt water or freshwater for further development. Nevertheless, for Suzuki (1998), newly hatched larvae died if not kept in saltwater. The spawning season is not known but it is expected from around April to November on Iriomote Island ( Suzuki, 1998). The species is thought to be diadromous. Tomita et al. (2016) examined the genetic population structure, genetic diversity and gene flow from the Philippines to southern Japan. Their study revealed high gene flow among the two localities, suggesting overall genetic homogeneity and a single shared gene pool, due to high dispersal ability during the oceanic larval stage and likely influence of the Kuroshio Current. According to Tomita et al. (2016) the species has declined around Japan because of environmental destruction, overexploitation, water pollution and the effects of invasive fish species. It is designated as ‘endangered’ in Japan.

Distribution: The species is known from Japan, Hong Kong, Taiwan, Palau and the Philippines ( Fig. 4).

Comparison: Hypseleotris everetti differs from the other species sequenced in having a significant percentage of divergence in the ND2 gene from 4.6% to 19.3% ( Table 3). Moreover, it differs from H. cyprinoides by a combination of characters including more pectoral fin rays (14–15 vs. 13–14), a greater head length (29–33 vs. 26–28% SL), a greater pre-dorsal length (40–46 vs. 37–41% SL), a greater body depth at anus in males (28–35 vs. 24–27% SL), a greater body depth at first dorsal fin in males (28– 35 vs. 23–27% SL) and females (26–29 vs. 22–26% SL), and a greater caudal peduncle depth (14–17 vs. 12–14% SL). It differs from H. alexis by more pectoral fin rays (14–15 vs. 13), fewer scales in lateral series (26–27 vs. 27–28), a greater body depth at anus in males (28–35 vs. 19–25% SL) and females (24–30 vs. 18–21% SL), a greater body depth at first dorsal fin in males (28–35 vs. 20–25% SL) and females (26–29 vs.18–21% SL), and a greater caudal peduncle depth (14–17 vs. 11–13% SL). It differs from H. moncktoni by more pectoral fin rays (14–15 vs. 13), fewer scales in lateral series (26–27 vs. 29) and in pre-dorsal series (15–17 vs. 19), and a greater head length (29–33 vs. 26% SL). It differs from H. ebneri in having fewer scales in pre-dorsal series (15–17 vs. 18–19), a greater body depth at anus in males (28–35 vs. 23–24% SL) and females (24–30 vs. 20–22% SL), a greater body depth at first dorsal fin in males (28–35 vs. 25% SL) and females (26–29 vs. 21–22% SL), and a greater caudal peduncle depth (14–17 vs. 11–14% SL). It differs from H. guentheri by more pectoral fin rays (14–15 vs. usually 13), fewer scales in lateral series (26– 27 vs. 28–29), a greater head length (29–33 vs. 25–28% SL), a greater pre-dorsal length (40–46 vs. 38–41% SL), a greater body depth at anus in males (28–35 vs. 18–21% SL) and females (24–30 vs. 19–24% SL), a greater body depth at first dorsal fin in males (28–35 vs. 18–21% SL) and females (26–29 vs. 18–25% SL), and a greater caudal peduncle depth (14–17 vs. 11–14% SL). It differs from H. compressa in having fewer scales in transverse back series (8–9 vs. 9–10), and in transverse forward series (9–11 vs. 12–14), more scales in pre-dorsal series (15–17 vs. 14–15) and more interorbital scales (2–3 vs. 0), and a second dorsal fin mostly I,8 vs. mostly I,9.