Hypseleotris alexis (Whitley, 1959)

HYPSELEOTRIS ALEXIS ( WHITLEY, 1959)

( FIGS 1–4, 8; TABLES 4, 5)

M a t e r i a l e x a m i n e d: H o l o t y p e: A M S I B.4 1 7 1, freshwater lake at Alexishafen , near Madang, Papua New Guinea. Paratypes: AMS IB.4172-76 (5), same data as holotype .

Note: Whitley did not separate the holotype from the paratypes and it is not clear which one is the holotype; five males, one female (39–45 mm SL) are mixed in AMS IB.4171-76 and not individually labelled.

Others: MNHN-IC-2015-0286, one female (36 mm SL); Solomon, Choiseul, Pisuku, 10 Dec. 2014, Keith, Boseto, Ebner et al. coll. MNHN-IC-2016-0202, one juvenile; Solomon, Kolobangara, Nov. 2015, Keith, Lord, Boseto et al. coll. MNHN-IC-2016-0205, two males (41–43 mm SL); Solomon, Kolobangara, Vanga, 18 Nov. 2015, Keith, Lord, Boseto et al. coll., tags A, B. MNHN-IC-2021-0294; Solomon, Santa Isabel, Kolopakissa, Station 15, 25 Oct. 2019, Keith, Lord, Boseto, Causse coll., tag. 17519. MNHN-IC-2021-0293, three males and one female (38.7–40.0 mm SL); Solomon Santa Isabel Rakata, Station, 27 Oct. 2019, Keith, Lord, Boseto, Causse coll., tags 17898, 17899, 17901. MNHN-IC-2021-0295, two males (30.3– 46.8 mm SL) and one juvenile; Papua New Guinea, New Britain, Nut Village , Water Lily Hole, 23 Oct. 2018, Keith, Lord, Amick, Causse et al. coll., tags 12539, 12542, 12544. MNHN-IC-2021-0299, two juveniles; Solomon, Santa Isabel Rakata-Station, 27 Oct. 2019, Keith, Lord, Boseto, Causse coll., tags 17897, 17900 .

Uncatalogued in MNHN: Vanuatu, Malekula , Mapes River, 30 Jan. 2010, Keith et al. coll., one sps, tag Hyp2. New Caledonia, Carénage/ Goro River, 25 Sept. 2020, Charpin N. coll., one sps, tag RTNC _051.

Description: The ray and scale counts are given in Table 4 and selected morphometrics in Table 5. The body is compressed laterally. Males often with a greater body depth than females: the body depth at anus is 18–21% SL for females, 19–25% SL for males, at first dorsal fin 18–21% SL for females, 20–25% SL for males, and the caudal peduncle depth is 11–13% SL. Pre-dorsal length 39–44% SL and preanal length 55–58% SL. Size: up to 6 cm SL.

The head is 27–31% SL, rounded dorsally with a broad interorbital, the snout is pointed. The mouth (terminal) and jaw length 6–8% SL are small; jaws oblique with several rows of conical teeth, 13–15 on first upper outer raw (the biggest in front are usually curved), 6–10 on the first lower outer row. Posterior end of maxillary ending below or just before 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 6–8% SL and interorbital length 6–8% SL.

Dorsal fins usually VI–I,8, with no filamentous rays. The first dorsal fin is with second, third, fourth and fifth rays longer. Anal fin I,9–10 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 13. Lateral scales 27–28, with ctenoid scales on flanks and caudal peduncle. Pre-dorsal scales usually cycloid anteriorly from snout adjacent to anterior nostril to anterior part of the head (but several specimens mostly with ctenoid scales), and usually with several ctenoid scales on a medium line before anterior part of D1. Ctenoid scales on operculum, on base of pectoral fins and on belly extending to anus. Cheek with cycloid and ctenoid scales. Scales in transverse back series 8–9, in transverse forward 9–10, in pre-dorsal usually 16–18 and in zigzag usually 6–7, interorbital scales 3–4. Vertebrae 25. Gill opening extending to below posterior preopercular margin.

Males have a more elongated second dorsal fin (25– 34 vs. 20–22% SL) and anal fin (27–33 vs. 22–26% 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 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 or beige on the back and the flanks; belly brown or beige. A greyish blotch on inferior part of caudal fin base. Top and middle of head brown, inferior part beige. Sometimes a thin dark stripe from snout and eye, across upper part of preoperculum and operculum, below midline ending at base of caudal fin. Males: First dorsal fin blackish to greyish with a superior white band, and white dots at the base. Second dorsal and anal fins with 2–4 rows of ovoid white spots or bands. Caudal fin greyish with 5–6 vertical rows of ovoid white spots. Females: Fins greyish to beige.

Colour in life: Breeding males are often more brightly coloured than females which are usually with lighter fins and body. Males ( Fig. 8A): Head and body yellowish brown to beige, white to grey on underside of head. Belly whitish to greyish. Two golden to silver spots on operculum with a pink to red background. A dark stripe from lower lip, snout and eye, across upper part of preoperculum and operculum, below midline ending at base of caudal fin. Pectoral fin base with a thin vertical dark bar. Caudal fin base with a small dot below midline. First dorsal fin blackish with a superior white band and white dots or a white band at the base. Second dorsal fin with 2–4 rows of ovoid white spots or a white band. Anal fin hyaline with 2–4 rows of ovoid white spots or hyaline. Tip of fins white. Caudal fin greyish with 5–6 vertical rows of ovoid white spots. Females ( Fig. 8B): Yellowish brown to beige. Fins hyaline. Head and body yellowish brown to beige, white to grey on underside of head. Belly whitish to greyish. Two golden to silver spots on operculum with a pink to red background. A dark stripe from lower lip, snout and eye, across upper part of preoperculum and operculum, below midline ending at base of caudal fin. Pectoral fin base with a thin vertical dark bar. Caudal fin base with a small dot below midline.

Ecology: Hypseleotris alexis was found in coastal rivers (pH 8.0–8.2, 130–160 µS/cm, 26.0–27.3 °C), small ponds and marshes with macrophytes ( Keith et al., 2021). As a free swimming species it is a predator, feeding on small invertebrates.

Distribution: The species is known from New Britain ( Papua New Guinea) and the Solomon Islands where it is common. It is rare in Vanuatu (Malekula) and New Caledonia ( Fig. 4).

Comparison: Hypseleotris alexis differs from the other species sequenced in having a significant percentage of divergence in the ND2 gene from 4% to 19% ( Table 3). Moreover, it differs from H. cyprinoides by a combination of characters including more scales in pre-dorsal series (16–18 vs. 14–16), a greater head length (28–31 vs. 26–28% SL), and a smaller body depth at anus (18–25 vs. 24–30% SL). It differs from H. everetti by fewer pectoral fin rays (13 vs. 14–15), more scales in lateral series (27–28 vs. 26–27), a smaller body depth at anus in males (19–25 vs. 28–35% SL) and females (18– 21 vs. 24–30% SL), a smaller body depth at first dorsal fin in males (20–25 vs. 28–35% SL) and females (18–21 vs. 26–29% SL), and a smaller caudal peduncle depth (11–13 vs. 14–17% SL). It differs from H. guentheri in having fewer scales in lateral series (usually 27–28 vs. usually 28–29), fewer scales in transverse back series (8–9 vs. 9–10), fewer scales in transverse forward series (9–10 vs. 10–11), and a greater head length (27–31 vs. 25–28% SL). It differs from H. ebneri in having fewer scales in pre-dorsal series (usually 16–18 vs. 18–19), fewer scales in transverse back series (8–9 vs. 9–10), and fewer scales in transverse forward series (9–10 vs. 10–12). It differs from H. compressa in having fewer pectoral rays (13 vs. 14–15), fewer scales in transverse forward series (9–10 vs. 12–14), more scales in pre-dorsal series (16–18 vs. 14–15) and in interorbital (3–4 vs. 0), a smaller body depth at first dorsal fin (18–25 vs. 24–35% SL), and a smaller body depth at anus in males (19–25 vs. 27–34% SL) and females (18–21 vs. 24–36% SL). It differs from H. moncktoni in having fewer scales in lateral series (26–28 vs. 29), fewer scales in transverse forward series (9–10 vs. 11), fewer scales in pre-dorsal series (usually 16–18 vs. 19), and a smaller body depth at anus in females (18–24 vs. 26% SL).