Cypselurus opisthopus ( Bleeker, 1865 )

Shakhovskoy, Ilia B. & Parin, Nikolay V., 2024, A review of the flying fish genus Cypselurus (Beloniformes: Exocoetidae). Part 3. Revision of the subgenus Cypselurus sensu stricto with descriptions of one new species and four new subspecies and reinstatement of Cypselurus crockeri Seale and Exocoetus socotranus Steindachner, Zootaxa 5473 (1), pp. 1-125 : 33-44

Cypselurus opisthopus ( Bleeker, 1865)

Synonymy and bibliography.

Exocoetus opisthopus Bleeker, 1865: 109 , 121–122 (original description; Celebes [Makassar]). Günther 1866: 297 (description, type; Celebes, Amboyna [ Ambon]). Bleeker 1866 –1872: 68, 76–77, Tab. CCXLVIII pl. Scombres II fig. 2 (description; Celebes (Makassar), Amboina [ Ambon]).

Exocoetus spilurus Günther, 1866: 285 (original description; locality unknown). Lütken 1876: 392, 396 (in part: a juvenile 1 inch length; Guimara, Philippines).

Cypsilurus opisthopus . Weber & de Beaufort 1922: 180, 190–192 (description; Indonesia). Fowler 1949: 58 (listed; Oceania).

Cypselurus spilurus . Fowler 1928: 85 (short description [after Günther 1866]). Munro 1958: 137 (listed; New Guinea). Munro 1967: 117, 121, pl. 13 fig. 191 (short description; New Guinea).

Cypselurus caudimaculatus Fowler, 1934a: 328 , fig. 82 (original description; Jolo Island, Philippines). Collette et al. 1992: 6 (description of holotype, synonymy with C. opisthopus ).

Cypselurus opisthopus .? Seale 1935: 348 (short description; Guadalcanal I.). Herre 1953: 162–163 (listed; Philippines; in part). Woods & Schultz 1953: 184–185, 187 (morphometry; Philippines). Munro 1958: 137 (listed; New Guinea). Parin 1958: 121 (distribution). Parin 1960a: 223, 256, 279 (description; western Pacific). Parin 1960b: 156 (distribution; western Pacific; in part?). Parin 1961a: 49–52 (description; western Pacific; in part). Parin 1961b: 99, 107, 109, 112, 117, 118, 129, 140, 165, figs. 7e, 8f, 17f (morphology, systematics). Munro 1967: 117, 121, pl. 13 fig. 192 (New Guinea; short description). Parin 1967: 45, 52, 54 (distribution, biology). Jinadasa 1971: 15–16 (short description; Sri Lanka; in part?).? Astakhov 1980: 207 (cranial lateral-line canals; 6°17’S 153°45’E). Kovalevskaya 1980: 224 (listed). Fedoryako 1982: 111 (juveniles listed as associated with drifted objects; Indo-Pacific). Kovalevskaya 1982: 116–117, figs. 5, 7 (juveniles; south of Sumatra).? Parin & Astakhov 1982: 277 (acustico-lateralis system).? Khachaturov 1983: 287–292, figs. 2d, 4e (digestive system; 13°31’S 139°58’E).? Hutomo & Burhanuddin 1985: 28–30 (listed; Indonesia). Fedoryako 1989a: 234 (listed as associated with drifted objects; in part). Fedoryako 1989b: 567 (listed). Jinadasa 1991: 109 (fishery; Sri Lanka). Dalzell 1993: 22–29, figs. 2–6 (fishery, biology; Camotes Sea, Philippines; in part). Lakshminaraina 1993: 30, fig. 4d (short description, distribution; “Indian seas”; in part?). Parin 1996: 302, 306 [359, 363] (distribution; western Pacific; in part). Parin 1999: 2166, 2175 (distribution, diagnostic characters, figure; western Pacific). Parin 2000: 600 (listed; South China Sea). Barman & Mishra 2006: 11 (listed in key; India).? Syahailatua et al. 2006 a: 263 (listed; eastern Indonesia). Fricke et al. 2019: 77 (listed; New Ireland). Shakhovskoy & Parin 2022: 88–89 (comparison with C. nossibe ).

Cheilopogon intermedius (non Parin).? Mohanty et al. 2021: 423–425, fig. 1 (description; Odisha Coast, Bay of Bengal; in part).

Probable misidentifications. Pajot & Prabhakaradu (1993: 2) reported C. opisthopus from Coromandel Coast of India; however it is probably a misidentification as their fishes were too large for this species— 23–35 cm long. Jayakumar et al. (2019: 698–701, figs. 1–3) described a specimen of C. opisthopus from Vizhinjam, India, but judging by its characters, they probably dealt with C. persimilis sp. n. (see below) or C. neglectus (Bleeker) .

Material examined. One hundred and forty-nine specimens of C. opisthopus opisthopus 19–186 mm SL. We compared samples from three geographic regions: the Indian Ocean, Philippines and New Guinea (as a border between two latter regions we used Wallace’s line of 1910 [see Fleminger 1986: fig. 1]).

New Guinea. Full morphological study . IORAS 04371 (1, 182 mm SL), Konstantin Harbour, New Guinea, 10.07.1971 . IORAS 04372 (1, 170 mm SL), same data . IORAS 04373 (1, 179 mm SL), same place, July 1971 . IORAS 04374 (1, 164 mm SL), same place, 10.07.1971 . IORAS 04375 (1, 170 mm SL), same data . IORAS 04376 (1, 148 mm SL), same data . IORAS 04377 (1, 181 mm SL), same place, 12.07.1971 . IORAS 04378 (1, 177 mm SL), same place, 11- 12.07.1971 . IORAS 04379 (1, 185.5 mm SL), same data . IORAS 04380 (1, 164 mm SL), same place, 10.07.1971 . IORAS 04381 (1, 176 mm SL), same place, 12.07.1971 . IORAS 04382 (1, 186 mm SL), same place, 11- 12.07.1971 . IORAS 04383 (1, 180 mm SL), same place, 12.07.1971 . IORAS 04384 (1, 180 mm SL), same place, 10.07.1971 . IORAS 04385 (1, 177 mm SL), same place, 12.07.1971 . IORAS 04386 (1, 160 mm SL), same place, 11- 12.07.1971 . IORAS 04387 (1, 177 mm SL), same data . IORAS 04388 (1, 180 mm SL), same place, 10.07.1971 . IORAS 04389 (1, 184.5 mm SL), same place, 12.07.1971 . IORAS 04390 (1, 183 mm SL), same place, 10.07.1971 . IORAS 04391 (1, 164 mm SL), same place, 11- 12.07.1971 . IORAS 04280 (1, 181 mm SL), Bongu, Maclay (Rai) Coast, 13.02.1977 . IORAS 04396 (1, 182 mm SL), Konstantin Harbour, New Guinea, 10.07.1971 . IORAS 04398 (1, 184 mm SL), Madang, New Guinea, 8- 12.04.1966 . IORAS 04401 (1, 173 mm SL), same data . IORAS 04402 (1, 179 mm SL), approaching to Rabaul, New Guinea, 4.01.1966 . IORAS 04407 (1, 159.5 mm SL), Madang, New Guinea, 8- 12.04.1966 . IORAS 04408 (1, 183.5 mm SL), same data . IORAS 04409 (1, 164.5 mm SL), same data . IORAS 04410 (1, 160 mm SL), same data . IORAS 04413 (1, 172 mm SL), same data . IORAS 04414 (1, 185 mm SL), same data . IORAS 04415 (1, 171.5 mm SL), same data . IORAS 04418 (1, 173 mm SL), same data . IORAS 04419 (1, 185 mm SL), same data . IORAS 04072 (1, 182 mm SL), 6°16’S 153°44’E, 28- 29.07.1957 . IORAS 04075 (1, 154.5 mm SL), 3°51’S 147°11’E, 7.08.1957 . IORAS 04079 (1, 114 mm SL), 5°34’S 131°04’E, 20- 21.04.1975 . IORAS 04086 (6, 66–121 mm SL), 5°38’S 147°04’E, 23- 24.05.1971 . IORAS 04087 (3, 90–110 mm SL), 0°59’N 134°31’E, 25- 26.08.1956 . IORAS 04088 (2, 42–57 mm SL), 0°39’– 0°04’S 148°13’– 148°20’E, 28.12.1965 . IORAS 04089 (1, 40 mm SL), 1°30’– 2°29’S 144°57’– 145°21’E, 26.04.1958 . IORAS 04090 (2, 171– 182 mm SL), Rabaul, New Guinea, 11- 12.05.1971 . IORAS 04092 (1, 153 mm SL), 5°38’S 147°04’E, 23- 24.05.1971 . IORAS 04093 (2, 156– 163 mm SL), Bongu, Maclay (Rai) Coast . IORAS 04097 (1, 99.5 mm SL), 3°06’N 128°09’E, 1.09.1957 . IORAS 04100 (2, 115– 130 mm SL), 0°16’N 137°33’E, 25.08.1957 . IORAS 04101 (4, 81–99 mm SL), ~ 3°47’S 144°45’E, 7.04.1966 . IORAS 04105 (8, 63–82.5 mm SL), ~ 1°S 143°E, 19.05.1971 . IORAS 04108 (1, 164 mm SL), 2°28’S 130°39’E, 23.03.1975 . AMS uncat (1, 26 mm SL), Madang, New Guinea, 26.09.1971 . AMS uncat (1, 153.5 mm SL), Sek Harbour, New Guinea, 20.09.1971 . SOSC uncat (1, 123 mm SL), off Biak I., Schouten Is., Indonesia, 30.06.1979 . ZMUC uncat (5, 158.5– 183 mm SL), 4°25’S 160°00’E, 6- 7.10.1951 .

Partial morphological study. IORAS 04406 (1, 183 mm SL), Madang , New Guinea 8- 12.04.1966 . IORAS 04094 (3, 30–53 mm SL), ~ 7°N 135°31’E, 1.06.1971 . IORAS 04107 (1, 87 mm SL), same place, 30.05.1971 . AMS I.16747-005* (1, 41 mm SL), 5°05’S 145°50’E, 30.09.1969 . AMS uncat (1, 19 mm SL), Madang , New Guinea, 18.09.1971 . CAS 129104 ( CAS-SU ( ICH) 69748)* (1, 155 mm SL), Ternate, Maluku Prov., Indonesia, 11.06.1929 . CAS 811893 * (1, 60 mm SL), 7°09’N 134° 25’E . USNM prereg. No. 18* (1, 158 mm SL), ~ Indonesia – Oceania . USNM prereg. No. 4430* (1, 140.5 mm SL), same place . ZMH 12752 * (1, 26 mm SL), New Guinea, May 1909 . ZMH 12772 * (1, 155 mm SL), Amboina , 15.01.1905 . Unknown collection, uncat* (1, 161 mm SL), Vitias Strait , 4- 5.02.1969 .

Philippines. Full morphological study. IORAS 04065 (3, 135– 154 mm SL), Philippines (Camotes Sea?) . IORAS 04084 (2, 95 mm SL), 8°18’N 120°25’E, 26.06.1971 . IORAS 04213 (1, 141 mm SL), 7°39’N 121°32’E, 28.02.1975 . IORAS 04102 (1, 104 mm SL), 6°20’N 122°36’E, 18.02.1973 . ZMUC P34917 (1, 152 mm SL), 9°33’N 122°19’E, 27.06.1929 . ZMUC P34920 (1, 166 mm SL), 2°08’N 125°21’E, 6.07.1929 . ZMUC uncat (3, 45–54 mm SL), 4°03’N 123°26’E, 2.04.1929 . ZMUC uncat (1, 99 mm SL), 2°54’N 120°04’E, 20.08.1951 .

Partial morphological study. IORAS 04067 * (2, 87–104 mm SL), 7°45’N 120°25’E, 4- 5.04.1961 . CAS 81782 * (2, 158– 163 mm SL), Zamboanga City Market, Night lights of St. Cruz I., 12.04.1948 . CAS 81806 * (1, 149 mm SL), Davao Harbour, 9.09.1948 . CAS 81832 * (2, 140– 147 mm SL), Siokun Bay, NW Zamboanga Peninsula, 11.03.1948 . CAS 81872 * (1, 147 mm SL), same place, 11- 12.03.1948 . CAS 81885 * (1, 160 mm SL), 6°44’N 125°37’E, 13.05.1948 . CAS 81891 * (1, 155 mm SL), 1°N 119°08’E, 1- 2.08.1948 . CAS 82046 * (1, 144 mm SL), 1°N 120°05’E, 12.04.1948 . CAS 82061 * (1, 118 mm SL), 7°27’N 121°43’E, 10.10.1947 . CAS 127269 ( SU 27269 )* (4, 144– 166 mm SL), Dumaguete, Negros Orient., Philippines, 11.07.1931 . CAS 138420 ( SU 38420 )* (2, 155– 162 mm SL), Mindanao I., Molugan: Cagayan, 12.04.1940 . QM I.11338* (1, 141 mm SL), Batangas Prov., Luzon . USNM 93070 * (holotype of C. caudimaculatus , 62 mm SL), Tutu Bay , Jolo I., 19.09.1907 . USNM 93071 * (paratypes of C. caudimaculatus ) (7, 37.5–50.5 mm SL), same place, 19.09.1907 . USNM 102557 # (1, ~ 153 mm SL), Iloilo ,

Panay I., 6.04.1929. USNM 137647 # (2, 153– 172 mm SL) , Malabang (Anchorage), Eastern Illana Bay, Southern Mindanao , 21.05.1908. USNM 137648 # (1, 172.5 mm SL) , Northern Mindanao and Vicinity: Camp Overton , Iligan Bay, 5.08.1909. USNM 226705 # (1, 145 mm SL) , Palawan, Togburos, Pto. Princesa City , June 1978 .

Indian Ocean. Full morphological study. IORAS 04078 (3, 114– 123 mm SL), 9°36’N 90°53’E, 13- 14.02.1961 . IORAS 04080 (1, 116 mm SL), 7°17’S 105°07’E, 16.07.1962 . IORAS 04085 (2, 87–122 mm SL), 8°10’S 104°39’E, 22- 23.03.1961 . IORAS 04096 (1, 125 mm SL), 5°37’N 94°46’E, 9.03.1961 . IORAS 04112 (1, 81 mm SL), 8°02’S 100°13’E, 22.11.1959 .

Partial morphological study. IORAS 04099 (1, 100 mm SL), 13°37’N 86°53’E, 2- 3.02.1961 . IORAS uncat* (1, 166 mm SL), 1°12’N 96°52’E, 12.03.1961 .

Locality unknown. Partial morphological study. BMNH 1866.5.2.32* (holotype of E. opisthopus , 184 mm SL), no data .

See additional material in the account for C. opisthopus crockeri .

Types. The holotype of Cypselurus opisthopus and types of Cypselurus caudimaculatus Fowler, 1934 and Exocoetus spilurus Günther, 1866 were studied by the second author. Their characters are given below.

Holotype of Cypselurus opisthopus ( Bleeker, 1865) ( Fig. 9 ). BMNH 1866.5.2.32, no label data 2. Length 184 mm SL. D 11, A 8, P I 13, Spred 29, Str 8, Sp.br 21 (4 + 17), Vert 42 (28 + 14). Measurements (in % SL): aV 66.5, cV 1 44.2, pV 32.2, c 23.6, Dc 23.2. First anal-fin ray beneath 5 th dorsal-fin ray. Upper and lower jaws of equal size, some of jaw teeth are tricuspid. Palatine teeth present. For the description of pigmentation see Günther 1866.

Holotype of Cypselurus caudimaculatus Fowler. USNM 93070, “Albatross”, Jolo Is., Tutu Bay, P.I., 19 September 1907. Length 62 mm SL (juvenile). D 11, A 7, P I 13, Spred 27? 3, Str -, Sp.br 25 (7 + 18), Vert 43 (29 + 14). Measurements (in % SL): cV 1 41.9, pV 33.2 (34.4 on the right side of body), c 22.4, o 8.8, io 1 9.8, H 13.7, h 6.1, Dc 26.1, lP -, lV 37.0, lcir 6.6. A small blackish chin barbel is forked at the apex. Pectoral fins pale with two large dark blotches, basally and distally. Pelvic and anal fins black, dorsal fin gray. Caudal fin pale with a dark spot on base of upper lobe.

Paratypes of Cypselurus caudimaculatus Fowler. USNM 93071, “Albatross”, Jolo Is., Tutu Bay, P.I., 19 September 1907. Seven juveniles 37.5–50.5 mm SL; specific data for three individuals provided below. Length 37.5 mm SL, Vert 43; measurements (in % SL): cV 1 44.5, pV 34.1, c 23.7, lcir 11.2. Pectoral fins pale, chin barbel forked. Length 48 mm SL, D 11, A 9, Vert 44 (29 + 15); measurements (in % SL): cV 1 43.5, pV 34.1, c 22.9, lcir 8.3. Chin barbel forked. Length 50.5 mm SL, D 10 or 11, Vert 44 (29 + 15); measurements (in % SL): cV 1 42.1, pV 32.0, c 23.5, lcir 6.9. Pectoral-fin pigmentation as in holotype, chin barbel forked. The remaining four paratypes with a dark spot on base of caudal-fin lower lobe, two with an unforked chin barbel .

Syntypes of Exocoetus spilurus Günther. BMNH 2012.11.8.1-2, Haslar collection, Locality unknown. Two juveniles 45–49 mm SL. Length 49 mm SL, D 11, A 8, Vert 42 (27 + 15), cV 1 46.9% SL, pV 34.6% SL. Chin barbel absent (according to Günther (1866), this specimen had a single flat barbel half as long as the head). Dark spot on caudal-fin base. Length 45 mm SL, D 12, A 9, Vert 43 (28 + 15), cV 1 43.3% SL, pV 34.4% SL. A short chin barbel. Dark spot on caudal-fin base. According to Fowler (1934a), E. spilurus has unforked barbel, unlike C. caudimaculatus .

Diagnosis. A small species of Cypselurus with many vertebrae and few dorsal-fin rays. Pelvic-fin base much closer to origin of caudal-fin lower lobe than head posterior edge. Body rather deep, head and eyes large, pelvic, pectoral and dorsal fins short. Jaw teeth mainly tricuspid and with additional cusps. Palatine teeth present. Juveniles with a short (forked or unforked) chin barbel and highly elevated dorsal fin; ventral side of body usually darker than dorsal one, caudal fin with a dark stripe through its base. In adults, pelvic fins usually sparsely pigmented and anal fin without black dots. D 10–12, Spred 25–34, Str 6½–8½, Vert 42–45 (28–30 + 13–16).

Description. Meristic and morphometric characters are given in Tables 1–7, 9 and 14. D 10–12 (usually 11–12), A 7–10 (usually 8–9), P I 12–15 (usually I 13–14), Spred 25–34 (usually 29–32), Str 6½–8½ (usually 7½–8½), Sp.br 21–28 (4–9 + 15–20), usually 23–25 (6–7 + 16–18), Vert 42–45 (28–30 + 13–16), usually 43–44 (28–29 + 14–15). Snout short ( Figs. 10 , 11b ), lower jaw shorter than upper jaw or, more rarely, jaws of equal size (in juveniles <135 mm SL lower jaw usually a bit longer than upper one). Upper jaw not pointed anteriorly. Juveniles <100 mm SL with a short (reaching from nostril to posterior edge of eye) flaccid (in smallest juveniles <30 mm SL the barbel is rather robust) chin barbel with a median keel (some fish without barbel starting with 81 mm SL). There is a

2 According to Günther (1866) the place of capture is Celebes.

3 Spred ~29 according to Collette et al. (1992).

TABLE 9. (Continued)

Measurements, % SL

Subspecies,

SL, mm

region

io1 Hc H h Dc lP lP1 lV lD lA HD HA p lcir

15.9 16.8 7.8 26.2 28.4 18.7 10.4 19.9 9.4 15.9

89.3 58.0 37.6 12.3

- (n=2) (n=2) (n=2) (n=2) (n=2) (n=2) (n=2) (n=2) (n=2) (n=2)

81.0–100.0 55.4–60.0 36.7–39.0 (n=1)

C. o. opisthopus 15.6–16.3 15.6–18.0 7.6–8.0 24.9–27.5 25.9–31.0 17.7–19.7 10.0–10.9 19.5–20.4 9.3–9.6 14.8–17.1

(Indian Ocean) 16.2 17.2 7.8 25.3 63.1 34.7 35.4 17.4 10.0 19.2 8.0 15.1

126.7

- (n=6) (n=6) (n=6) (n=6) (n=6) (n=6) (n=6) (n=6) (n=6) (n=6) (n=5) (n=6) -

114.0–166.0

15.6–16.6 16.2–18.6 7.6–7.9 24.4–25.9 60.0–67.3 31.6–39.0 34.0–36.5 16.1–18.7 8.4–11.2 18.2–20.4 7.7–8.2 14.8–15.5

15.5 15.7 7.1 25.1 51.5 29.5 36.2 17.4 10.1 16.6 8.9 14.7

65.8 9.8 9.1 (n=7)

(n=6) (n=7) (n=7) (n=7) (n=6) (n=5) (n=7) (n=6) (n=6) (n=6) (n=5) (n=6)

37.5–99.0 (n=1) 6.6–13.8

C. o. opisthopus 13.3–17.2 13.3–18.2 6.1–7.6 24.0–26.3 43.1–59.8 24.8–34.1 34.5–38.2 16.8–18.2 9.2–10.8 14.0–18.9 7.2–10.1 13.1–15.7 ( Philippines) 16.7 18.7 7.4 24.6 63.0 38.7 28.8 16.7 11.8 7.6 14.1

147.8 7.5 9.7 (n=7)

(n=6) (n=7) (n=7) (n=16) (n=7) (n=11) (n=10) (n=7) (n=6) (n=5) (n=7) -

104.0–172.5 (n=1) 8.4–12.6

16.1–17.3 17.2–20.1 7.1–7.8 23.4–25.9 58.4–66.0 33.8–40.4 26.2–35.6 15.0–18.3 10.7–14.4 6.7–9.4 13.3–15.0

16.0 16.7 7.6 25.3 52.3 30.0 36.7 17.7 9.8 16.8 9.1 15.1 8.2

68.8

- (n=23) (n=23) (n=23) (n=25) (n=27) (n=24) (n=26) (n=23) (n=23) (n=23) (n=21) (n=23) (n=22)

19.0–99.5

C. o. opisthopus 13.0–17.8 13.0–20.2 7.0–8.1 23.0–27.5 33.5–60.8 22.1–33.0 27.0–39.6 16.0–20.0 8.7–11.4 14.2–19.3 8.3–10.4 11.8–16.1 4.8–12.6 (New Guinea) 8.3 17.6 19.5 7.3 24.9 62.5 38.1 29.2 16.6 8.9 13.3 7.3 14.7

164.9

(n=2) (n=54) (n=51) (n=56) (n=58) (n=36) (n=46) (n=38) (n=57) (n=55) (n=17) (n=24) (n=56) -

102.0–186.0

8.1–8.5 15.3–19.5 17.4–21.8 6.4–8.4 23.0–26.7 57.7–67.0 32.3–44.1 26.0–35.4 15.1–18.4 7.6–10.0 10.2–18.3 6.4–8.5 13.5–15.7

15.9 16.5 7.5 25.3 52.6 29.8 36.7 17.7 9.9 17.0 9.1 15.1 8.5

69.4 9.8

(n=31) (n=32) (n=32) (n=34) (n=36) (n=31) (n=36) (n=31) (n=31) (n=31) (n=28) (n=31) (n=30)

19.0–100.0 (n=1)

C. o. opisthopus 13.0–17.8 13.0–20.2 6.1–8.1 23.0–27.5 33.5–60.8 22.1–34.1 27.0–39.6 16.0–20.0 8.7–11.4 14.0–20.4 7.2–10.4 11.8–17.1 4.8–13.8 (all regions) 8.0 17.4 19.2 7.4 24.9 62.6 37.9 29.8 16.7 9.1 14.2 7.4 14.7

157.3

(n=3) (n=66) (n=64) (n=69) (n=81) (n=49) (n=63) (n=54) (n=70) (n=68) (n=29) (n=34) (n=69) -

102.0–186.0

7.5–8.5 15.3–19.5 16.2–21.8 6.4–8.4 23.0–26.7 57.7–67.3 31.6–44.1 26.0–36.5 15.0–18.7 7.6–12.6 10.2–20.4 6.4–9.4 13.3–15.7

17.1 18.7 62.1 36.8 15.2 7.9

162.5 7.4 24.5 30.7 16.8 10.1 15.0

C. o. crockeri - (n=10) (n=11) (n=10) (n=9) (n=7) (n=7) - 134.0–183.0 6.9–8.1 23.1–26.7 26.0–36.8 15.2–18.5 9.2–11.1 14.2–16.1

16.4–18.2 16.6–20.8 59.7–64.6 33.7–40.2 10.8–21.4 7.1–8.8

dimorphism in barbel morphology: the majority of juveniles have a barbel forked along ½–¾ of its length, while others have a simple barbel ( Fig. 12 ). Jaw teeth numerous, small to medium-sized (not visible or barely visible to naked eyes); teeth of two types (tricuspid and teeth with additional cusps) prevail, but conical teeth usually also present (fish <100 mm SL usually with conical teeth only). In adults, teeth arranged in 2–4 rows; in juveniles <110 mm SL in 1–2 rows. Palatine teeth present, usually numerous.

Body elongate in juveniles and rather deep in adults ( Fig. 10 ): in juveniles 25–100 mm SL body depth 4.95–7.7 in SL; in fish 110–185 mm SL, 4.6–6.2 in SL. Body width 0.91–1.45 and caudal peduncle depth 1.86–3.15 in greatest body depth. Greatest head depth slightly increasing with growth: in juveniles 25–100 mm SL, 5.6–7.7 in SL and in fish 110–185 mm SL, 5.1–6.55 in SL. Head length not changing with growth, 3.85–4.65 in SL and 0.90–1.20 in dorso-caudal distance. Eyes large, eye diameter decreasing with growth: in juveniles 20–100 mm SL eye 9.1–13.15 in SL, 2.25–3.1 in head length, 0.9–1.45 in interorbital width and 0.95–1.5 in postorbital distance; in fish 110–185 mm SL, 11.2–14.7 in SL, 2.8–3.45 in c, 1.0– 1.35 in io and 1.1–1.6 in po. Snout length strongly increasing with growth ( Fig. 11b ).

Pectoral fins relatively short, their length strongly increasing with growth to about 120 mm SL, and afterwards nearly constant ( Fig. 4 ): in juveniles 25–100 mm SL pectoral fin 1.65–3.0 in SL and in fish 110–185 mm SL, 1.45–1.75 in SL. Tip of pectoral fin reaching from middle to end of dorsal-fin base (occasionally slightly beyond); in fish 60–100 mm SL from origin to middle of dorsal-fin base, in fish 30–60 mm SL from pelvic-fin base to dorsal-fin origin, and in fish 19–26 mm SL to ½–⅔ of distance between pectoral and pelvic fins. First pectoral-fin ray unbranched, its length increasing with growth: in juveniles 25–100 mm SL it fits 2.9–4.5 in SL and 1.51–2.14 in lP; in fish 110–185 mm SL, 2.25–3.15 in SL and 1.52–1.90 in lP. Pelvic-fin base closer to origin of caudal-fin lower lobe than to posterior edge of head (cV / pV = 1.04–1.52). Pelvic-fin length decreasing strongly from juveniles to adults ( Fig. 11c ): in juveniles 40–100 mm SL pelvic fin 2.5–2.9 in SL and 1.14–1.70 in lP; in fish 110–185 mm SL, 2.7–3.85 in SL and 1.65–2.37 in lP. Tip of pelvic fin in smallest juveniles 19–26 mm SL reaching from end of anal-fin base to middle of caudal peduncle; in juveniles 30–135 (147 in C. opisthopus crockeri ) mm SL protruding beyond origin of caudal-fin lower lobe; in fish> 135 mm SL reaching from end of anal-fin base to middle of caudal peduncle (rarely beyond).

Anal-fin origin far posterior to dorsal-fin origin (1st anal-fin ray under 4th–7th dorsal-fin ray, usually under 5th–6th). Dorsal fin with 2–4 rays more than anal fin. Height of dorsal fin strongly increasing with growth up to 130 (147 in C. o. crockeri ) mm SL and afterwards abruptly slumping ( Fig. 11d ) probably due to sloughing of dorsal-fin’s melanistic lobe (see Breder & Rasquin 1952 for description of the process): in juveniles 40–130 (147 in C. o. crockeri ) mm SL HD fits 4.65–7.15 in SL and in fish 135–185 mm SL, 7.9–9.8 in SL. Height of anal fin, on the contrary, steadily decreasing with growth ( Fig. 11e ): in juveniles 40–100 mm SL it fits 9.6–13.9 in SL and in fish 110–185 mm SL, 11.35–15.6 in SL. Longest dorsal-fin ray in juveniles 40–130 (147 in C. o. crockeri ) mm SL—6th–9th, in fish> 135 mm SL—2nd or, rarely, 3rd. Longest anal-fin ray both in juveniles and adults—2nd or 3rd. In juveniles 30–130 (147 in C. o. crockeri ) mm SL tip of last dorsal-fin ray protruding beyond origin of caudal-fin upper lobe, middle and posterior rays of dorsal fin highly elongate, penultimate rays always extending far beyond tip of last ray ( Fig. 10 ). In smallest juveniles 19–26 mm SL and in fish> 135 mm SL tip of last dorsal-fin ray protruding beyond middle of caudal peduncle but usually not reaching origin of caudal-fin upper lobe, middle and posterior rays of dorsal fin not elongate, penultimate rays never extending beyond tip of last ray.

Pigmentation. Body of fish 20–130 (147 in C. o. crockeri ) mm SL brown to dark brown ( Fig. 10a–e ), ventral side usually darker than dorsal one, in some fishes with golden or silvery shine. Body bands absent. In fish> 130 mm SL body with typical “pelagic” pigmentation ( Fig. 10f ).

The ventral surface of the head of juveniles 20–130 (147 in C. o. crockeri ) mm SL dark brown with paler “lips” ( Fig. 12 ) and margin of gill cover (smaller juveniles ≤ 30 mm SL also with paler branchiostegal rays). In fish> 140 mm SL ventral surface of the head mostly pale. Numerous small dark specks ( Fig. 10g ) usually present on gill cover and under eye (in some fish also on body); the specks are probably covered with iridocytes in life. Chin barbel ( Fig. 12a ) in juveniles <40 mm SL brown or dark brown with paler base and tip (in a fish 39.5 mm SL unforked barbel also with a pale median keel). Juveniles ≥ 40 mm SL with barbel (both forked and unforked) either mainly pale or mainly dark (pale brown to brown) ( Fig. 12b–e ). Pigmentation of barbel’s opposite (ventral) side usually about the same as described above.

Pectoral fins of juveniles 19–45(53) mm SL pale with dense brown pigmentation on fin base ( Fig. 13a ) and, in some fish, also weak pigmentation distally. In fish 50–60 mm SL pectoral fins pale with two large dark blotches basally and distally. In fish 60–100 mm SL these two blotches expand and merge, and pectoral fin gets brown or dark brown to 7th–9th ray with a small pale “mirror” to 6th–7th ray and with 1–6 pale oval spots (or a pale “mirror”) superiorly4 ( Fig. 13b ), upper margin of fin mainly pale. In fish 100–135 mm SL (starting with 75 mm SL for New Guinea fish) pectoral fin brown to dark brown to 8th–9th ray with a pale tip and a small pale “mirror” to 7th–8th ray ( Fig. 13d ). In fish ≥ 135 mm SL pectoral fin pale brown to dark brown to (7)8–9 ray with a pale tip and usually with a very narrow pale posterior edging ( Fig. 13e ). Pigmentation usually extending one ray lower distally than proximally, occasionally a small pale “mirror” present.

Pelvic fins of juveniles 20–130 mm SL (up to 147 mm SL in C. o. crockeri ) ( Figs. 10a–b , 14a–c ) brown to dark brown with pale outer margin (1st ray and outer branch of 2nd ray distally) and area between 5th and 6th rays distally (in fish> 80 mm SL pigmentation also tends to disappear proximally, Fig. 14b–c ). In fish 135–145 mm SL pelvic fins pale with brown pigmentation mainly between 2nd–4th rays. In fish> 145 mm SL pelvic fins pale with vestigial dotted pigmentation between 2nd–4th rays ( Fig. 14d ), rarely entirely pale. In C. o. crockeri pelvic fins retain rather dense brown pigmentation between 2nd–4th(5th) rays to 180 mm SL.

Dorsal fin of juveniles 20–50(55) mm SL covered with brown melanophores (mainly near fin base and in upper portion, anterior part pigmented only basally). In fish 50–130 (147 in C. o. crockeri ) mm SL, dorsal fin brown to dark brown, anterior part usually slightly paler, sometimes with an oblique paler stripe (or 1–2 rows of spots) ( Fig. 10c–e ). In fish ≥ 135 mm SL dorsal fin gray to pale-brownish ( Fig. 10f ).

Anal fin of juveniles 20–45(54) mm SL pale with brown pigmentation only near fin base and between 2–3 posterior rays ( Fig. 10a ). In fish 45–130 mm SL, anal fin brown or dark brown with pale anterior corner ( Fig. 10c ) or anterior edging. In fish> 100 mm SL pigmentation starts to disappear near fin base and along posterior margin. In fish ≥ 135 mm SL anal fin devoid of pigmentation (in C. o. crockeri a brown distal spot present up to 147 mm SL, and in some adults a few dots between rays persist).

Caudal fin of juveniles 20–60 mm SL pale with brown to dark brown (sometimes nearly black) stripe through fin base and brown pigmentation between rays of lower lobe (sometimes also with sparce melanophores between rays of upper lobe) ( Fig. 10a–b ). In juveniles 60–115 mm SL 1–2 dark bands appear on lower lobe ( Fig 10c ). Fish 115–130 mm SL (up to 147 mm SL in C. o. crockeri ) with 2–3 bands on lower lobe (sometimes also with a band on upper lobe) ( Fig. 10e ). In fishes ≥ 135 mm SL caudal fin greyish brown to brown ( Fig. 10f ), usually with slightly darker base.

4 Such pale spotting may occasionally be retained in much larger fish: 121 mm SL in C. opisthopus opisthopus (IORAS 04078) and 134 mm SL in C. opisthopus crockeri (IORAS 04098).

Coloration in life. In juveniles of C. o. opisthopus 87 and 122 mm SL (IORAS 04085) the dorsal fin was yellow with reddish and black streaking, its posterior lobe black and the caudal-fin lower lobe had red bands in life. According to Seale (1935), the holotype of C. o. crockeri 147 mm SL was blue on back, silvery below; pectoral, pelvic, dorsal and anal fins black, upper lobe of caudal fin gray, lower lobe with three red bars.

Maximum size. The maximum length of C. o. opisthopus in the material examined was 186 mm SL ( IORAS 04382 , female). The largest male was 164 mm SL ( IORAS 04374 ) . The largest female of C. o. crockeri was 183 mm SL ( ZMUC uncat., 4°25’S 160°00’E) and the largest male was 164 mm SL ( IORAS 04109 ) .

Intraspecific variation. Fish from Melanesia ( Fig. 8a ) have some distinctive features (see below) that allow us to separate them in a subspecies— C. o. crockeri Seale. The samples of C. o. opisthopus from the Indian Ocean, Philippines and New Guinea only negligibly differ in frequencies of dorsal- and pectoral-fin rays, gill rakers on the upper limb of arch and vertebrae ( Tables 1, 5–6). Also, there are subtle differences in some morphometric characters ( Tables 9, 14; Fig. 11 ): fish from the Indian Ocean have a more elongated body and higher dorsal fin, and fish from Philippines have a narrower body with a more posterior position of pelvic-fin base. Fish from New Guinea lose juvenile pigmentation of pectoral fins as early as 75 mm SL vs. 100 mm SL in fish from other regions (see above). We do not regard these differences as taxonomically significant.

Juveniles of C. o. opisthopus are dimorphic in chin barbel morphology ( Fig. 12 ). The juveniles with a forked and unforked barbel are sympatrically distributed ( Fig. 8b ), and comparison of these two morphs shows no appreciable differences in pigmentation, meristic and morphometric characters, except juveniles with unforked barbel have more posterior position of pelvic-fin base (index cV/pV 1.18–1.46, mean 1.30 ± 0.025, n=9 vs. 1.04–1.28, mean 1.18 ± 0.017, n=16). We regard these forms as conspecific here, however further study is needed as two cryptic species may exist. Juveniles of C. o. crockeri remain unknown.

Comparative remarks. Abe (1953) regarded C. hiraii as a subspecies of C. opisthopus . However, the vast majority of subsequent authors regarded C. hiraii as a distinct species. Indeed, C. opisthopus differs from C. hiraii in most of characters studied: teeth structure (mainly tricuspid and with additional cusps in C. opisthopus vs. mainly conical in C. hiraii ), number of dorsal-fin rays (10–12 vs. 12–15, usually ≥ 13), transverse scales (6½–8½ vs. 8–10, usually 9–9½), gill rakers (21–28, usually 23–25 vs. 23–32, usually 26–29), vertebrae (42–45, usually 43–44 vs. 45–47, usually 46–47), position of pelvic-fin base (pV 29.3–37.5, usually <36.0 vs. 35.2–41.6, usually> 36.0% SL) and many others (see Table 7, Fig. 4a–f ). Juveniles also differ in shape of chin barbel (compare Figs. 2 and 12 ), height of dorsal fin (in fish ≤ 130 mm SL, HD 14.0– 20.4 in C. opisthopus vs. 10.9–13.1% SL in C. hiraii ) and pigmentation of body, pectoral and caudal fins (see descriptions above).

Cypselurus opisthopus differs from all species of the subgenus Poecilocypselurus and C. nossibe in more posterior position of pelvic-fin base (index cV/pV> 1.00 vs. 0.48–1.05, usually <1.00). Occasional specimens of C. neglectus shcherbachevi Shakhovskoy & Parin and C. nossibe may be hard to distinguish from C. opisthopus based on position of pelvic-fin base alone. In that case number of vertebrae, predorsal and transverse scales should also be taken into consideration.

Cheilopogon papilio (Clark) from the eastern Pacific Ocean also has posteriorly shifted pelvic fins, but this species differs from C. opisthopus (not occurring in the eastern Pacific) in absence of palatine teeth, fewer dorsal-fin rays, more anal-fin rays and gill rakers, smaller eye, shorter Dc, lV and lD and longer lP and lP 1, as well as in other features ( Ch. papilio will be described in detail in a subsequent publication).

Biology. Females and males of C. opisthopus are mature starting at 165 and 155 mm SL, respectively. Recently spent, mature and close to mature females were captured in February (IORAS 04280, Bongu), April (IORAS 04398, 04401, 04406, 04414 and 04418–04419, Madang), May (IORAS 04090, Rabaul; IORAS 04091, Ninigo Is. [ crockeri ]), July (IORAS 04071, 6°16’S 153°44’E ( crockeri ); IORAS 04371–04373, 04375, 04377–04378, 04381– 04383, 04385 and 04387–04390, Konstantin Harbour; ZMUC P34920, 2°08’N 125°21’E) and October (ZMUC uncat., 4°25’S 160°00’E [both opisthopus and crockeri ]). Small juveniles were captured in May (26 mm SL, ZMH 12752, New Guinea) and September (19 mm SL, AMS uncat., Madang). Therefore, C. opisthopus seemingly spawns nearly year-round (probably with interruption only from November to January). Spawning season of C. o. crockeri is probably at least from May to October.

Distribution. Distribution of C. opisthopus and its subspecies is given in Figure 8 . According to our data, this species is distributed in tropical waters between 12°S and 14°N from Bay of Bengal (IORAS 04099, 13°37’N 86°53’E) to Solomon Islands (IORAS 04109, 8°10’S 163°00’E). Cypselurus opisthopus is a neritic species, but probably avoids areas with wide continental shelf. Juveniles of C. opisthopus are frequently associated with flotsam ( Fedoryako 1982). Cypselurus o. crockeri distributed mainly in waters of Solomon Islands (where C. o. opisthopus seems to be very rare), with the westernmost occurrence at Ninigo Is. (IORAS 04091). The population of C. o. opisthopus from the Indian Ocean seems to be isolated from the Pacific one.

Additional occurrences of C. opisthopus are listed in the Synonymy and bibliography section. Jinadasa (1971, 1991) reported C. opisthopus from Sri Lanka and Mohanty et al. (2021) described (as Cheilopogon intermedius Parin ) probably this species from the Odisha Coast, Bay of Bengal.

Nguyen & Nguyen (1994: 151–152) and Mai & Bui (1978: 251, 261) listed C. opisthopus for waters of Vietnam, but these authors did not provided any characters and, because C. opisthopus was not found in the South China Sea ( Fig. 8 ), we suppose that this occurrence needs confirmation as misidentification of C. naresii is probable. Parin (1996) reported C. opisthopus in the waters of Okinawa (based on URM P27993); however, in the present work we re-identified this specimen as C. persimilis sp. n. (see below).

Figures

FIGURE 2. Chin barbel of Cypselurus hiraii (ventral view of head). (A)—47 mm SL, IORAS 04133, 41°35–58’N 138°28’E; (B)—50 mm SL, IORAS 04132, 41°31’N 142°17’E; (C)—52 mm SL, IORAS 04132, same place; (D)—61.5 mm SL, IORAS 04127, 37°N 160°E; (E)—71 mm SL, IORAS 04133, 41°35–58’N 138°28’E

FIGURE 4. Size variation of morphometric characters (in % SL) in Cypselurus hiraii (◊), C. opisthopus (∆), C. naresii (○), C. persimilis (+), C. angusticeps (□) and C. comatus (x): (A)—cephalo-ventral distance divided by postventral distance (index cV/ pV); (B)—dorso-caudal distance (Dc); (C)—pectoral-fin length (lP); (D)—length of the first pectoral-fin ray (lP1); (E)—height of dorsal fin (HD); (F)—length of chin barbel (Lcir).

FIGURE 8. Distribution of Cypselurus hiraii and C. opisthopus. (A)—distribution of C. hiraii (□) and C. opisthopus (○—C. o. opisthopus, ∆—C. o. crockeri). Filled symbols indicate capture location for fishes ≤ 100 mm SL, open symbols indicate capture location for fishes> 100 mm SL; holotype position marked with asterisk. (B)—distribution of barbelled juveniles of C. o. opisthopus (+—juveniles with forked barbel; x—juveniles with unforked barbel).

FIGURE 9. Cypselurus opisthopus (from Bleeker 1866-1872, likely the holotype).

FIGURE 10. Cypselurus opisthopus opisthopus. (A)—19 mm SL, AMS uncat., Madang; (B)—42 mm SL, IORAS 04088, 0°39’–0°04’S 148°13’–148°20’E; (C)—68 mm SL, IORAS 04105, ~ 1°S 143°E; (D)—99 mm SL, ZMUC uncat., 2°54’N 120°04’E; (E)—125 mm SL, IORAS 04096, 5°37’N 94°46’E; (F)—171 mm SL, IORAS 04090, Rabaul; (G)—154.5 mm SL (close up of head), IORAS 04075, 3°51’S 147°11’E.

FIGURE 11. Size variation of morphometric characters (in % SL) in Cypselurus opisthopus opisthopus (□—Indian Ocean, ◊—Philippines, ∆—New Guinea) and C. o. crockeri (●). (A)—postventral distance (pV); (B)—snout length (ao); (C)—pelvicfin length (lV); (D)—dorsal-fin height (HD); (E)—anal-fin height (HA); (F)—body width (p).

FIGURE 12. Chin barbel of Cypselurus opisthopus opisthopus (ventral view of head). (A)—19 mm SL, AMS uncat., Madang; (B)—57 mm SL, IORAS 04088, 0°39’–0°04’S 148°13’–148°20’E; (C)—72 mm SL, IORAS 04105, ~ 1°S 143°E; (D)—72 mm SL, IORAS 04105, same place; (E)—82 mm SL, IORAS 04086, 5°38’S 147°04’E.

FIGURE 13. Pectoral fins of Cypselurus opisthopus opisthopus. (A)—45 mm SL, ZMUC uncat., 4°03’N 123°26’E; (B)—63 mm SL, IORAS 04105, ~ 1°S 143°E; (C)—102 mm SL, IORAS 04086, 5°38’S 147°04’E; (D)—123 mm SL, IORAS 04078, 9°36’N 90°53’E; (E)—182 mm SL, IORAS 04072, 6°16’S 153°44’E.

FIGURE 14. Pelvic fins of Cypselurus opisthopus opisthopus. (A)—74 mm SL, IORAS 04105, ~ 1°S 143°E; (B)—95 mm SL, IORAS 04084, 8°18’N 120°25’E; (C)—125 mm SL, IORAS 04096, 5°37’N 94°46’E; (D)—164 mm SL, IORAS 04108, 2°28’S 130°39’E.