Polydactylus luparensis, Lim, Pek Khiok Annie, Motomura, Hiroyuki & Gambang, Albert Chuan, 2010

Lim, Pek Khiok Annie, Motomura, Hiroyuki & Gambang, Albert Chuan, 2010, Polydactylus luparensis, a new species of threadfin (Perciformes: Polynemidae) from the Batang Lupar River, Sarawak, Borneo, Malaysia, Zootaxa 2405, pp. 63-68 : 64-67

Polydactylus luparensis n. sp.

New English name: Sarawak Giant Threadfin (Fig. 1; Table 1)

Holotype. IPPS 08-01, 670 mm SL, mouth of Batang Lupar River, Sarawak, Malaysia, Borneo, 01°27’68”N, 111°01’83”E, 3–5 m depth, gill net, P. K. A. Lim et al., FRV Blue Lagoon, 7 May 2008.

Paratypes. IPPS 08-02, 675 mm SL, same data as holotype except for date, 20 June 2008; IPPS 08-04, 640 mm SL, same data as IPPS 08-02; IPPS 08- 231, 715 mm SL, same data as holotype except for date, 3 Aug. 2008; KAUM –I. 13252, 610 mm SL, same data as IPPS 08-02.

Diagnosis. A species of Polydactylus that differs from all of its congeners by the following combination of characters: 8 dorsal-fin spines, first spine tiny, second spine very strong (its width more than 5 times of width of remaining spines); 13 second dorsal-fin soft rays; 11 anal-fin soft rays; 12 pectoral-fin rays, its length 22–24% (mean 23%) of SL, posterior tip not reaching a vertical through posterior tip of depressed pelvic fin; 6 pectoral filaments, fourth or fifth filament longest, its length 77–85% (mean 81%) of SL, posterior tip extending slightly beyond caudal-fin base; pored lateral-lined scales 67–75 (mean 71); lateral line unbranched, extending onto upper end of lower caudal-fin lobe; 6 scale rows above lateral line, 8 below; 14 gill rakers on upper limb, 18 on lower limb, 32 in total; occipital profile concave; posterior margin of maxilla extending considerably beyond a vertical through posterior margin of adipose eyelid; depth of posterior margin of maxilla 4–5% (mean 5%) of SL, greater than orbit diameter; well-developed swimbladder present; basal half of third to sixth pectoral filament white, becoming black distally.

Description. Counts and proportional measurements of the holotype and paratypes of Polydactylus luparensis are given in Table 1. Characters given in the diagnosis are not repeated.

Body oblong, moderately compressed. Head large, its length greater than body depth. Eye very small, 6.9% (7.5–8.7%, mean 7.8%) of head length, covered with thick adipose eyelid; longitudinal length of adipose eyelid more than half of upper-jaw length. Anterior nostril and posterior nostril very similar in size. Maxilla covered with scales; lower lips well developed. Teeth villiform, in broad bands on vomer, palatines and ectopterygoids; tooth band of upper jaw wider than that of lower jaw; tooth band of upper jaw wider than width of space separating tooth bands on opposing premaxilla; length of palatine plate longer than that of ectopterygoid plate. Preopercular margin serrated. All pectoral-fin rays unbranched. First pectoral filament not reaching posterior tip of depressed pelvic fin; second filament extending beyond posterior tip of depressed pelvic fin, but not reaching posterior end of anal-fin base; third filament reaching (just short of in two paratypes) middle of caudal peduncle; fourth filament extending slightly beyond caudal-fin base; fifth filament just reaching (extending slightly beyond in two paratypes) caudal-fin base; sixth filament subequal to third filament. Scales covering entire body and head, except for lips and adipose eyelid.

Color when fresh —Body grayish blue dorsally, silvery ventrally. First and second dorsal-fin spines gray, remaining dorsal-fin spines whitish; dorsal-fin membranes semitransparent white. Second dorsal, pelvic, anal, and caudal fins dull white. Pectoral fin rays white, membranes semitransparent white. First and second pectoral filaments white entirely; third to sixth filaments white basally, dense black distally.

FIGURE 1. Polydactylus luparensis from Batang Lupar River, Sarawak, Borneo. A, fresh specimen, IPPS08-01, holotype, 670 mm SL. B, fresh specimen, IPPS08-231, paratype, 715 mm SL. C, preserved specimen, IPPS08-01, holotype, 670 mm SL.

Color of preserved specimens — Body gray dorsally, yellowish white ventrally. Dorsal-fin spines gray; fin membranes semitransparent white. Second dorsal, pelvic, and anal fins yellowish white. Upper margin of upper caudal-fin lobe blackish, remaining portion of fin yellowish white. Pectoral fin rays yellowish white, fin membranes semitransparent white. First and second pectoral filaments yellowish white entirely; third to sixth filaments yellowish white basally, dense black distally.

Distribution. Currently known only from the mouth of the Batang Lupar River, Borneo, Malaysia, inhabiting turbid brackish water. The species is abundant in the river mouth especially from June to August and mainly caught by gill nets. Juveniles have also been observed in the same place (local fishermen, pers. comm.).

Etymology. The specific name luparensis is based on the Batang Lupar River in reference to the holotype locality. Local name of this species is Gemian.

Remarks. Polydactylus luparensis can be easily distinguished from all Indo-Pacific congeners by having the black distal half of the third to sixth pectoral filaments (whitish in the latter). Only two other taxa, Polynemus melanochir dulcis Motomura & Sabaj, 2002 and P. melanochir melanochir Valenciennes in Cuvier & Valenciennes, 1831, in the family Polynemidae have the black pectoral filaments ( Motomura & Sabaj, 2002; Motomura, 2004b).

The new species has long pectoral filaments, the longest extending beyond the caudal-fin base, whereas all species of Polydactylus , except for P. macrophthalmus and P. longipes Motomura et al., 2001 a, have short filaments, not reaching the midpoint of the anal-fin base ( Motomura et al., 2001a; Motomura, 2004b). Polydactylus macrophthalmus is similar to P. luparensis in overall appearance, including the long pectoral filaments and a concave occipital profile, but the former differs from P. luparensis in having seven pectoral filaments (vs. six in the latter), 13 or 14 pectoral-fin rays (vs. 12), 87–94 pored lateral-line scales (vs. 67–75), 11 scale rows above the lateral line and 15 or 16 scale rows below (vs. six and eight), and 10–12 gill rakers on the upper limb, 15 or 16 rakers on the lower limb, and 26 or 27 rakers in total (vs. 14, 18, and 32), in addition to the differences of pectoral-filament coloration. Although P. longipes shares six long pectoral filaments with P. luparensis , it differs from P. luparensis by having 12 dorsal-fin soft rays (vs. 13 in the latter), 13 pectoralfin rays (vs. 12), 54 or 55 pored lateral-line scales (vs. 67–75), 11 scale rows below the lateral line (vs. eight), and grayish black body (vs. silvery). The two species further differ in 25 morphometrics (see Motomura et al., 2001a: table 1), including orbit diameter 10–11% of SL in P. longipes vs. 3% in P. luparensis . Data for P. longipes and P. macrophthalmus are based on Motomura et al. (2001a, b) respectively.

Polydactylus luparensis attaining 715 mm SL and 890 mm TL (IPPS 08-231) appears to be the second largest species of the genus in the Indo-Pacific after P. macrochir ( Günther, 1867) , validate ageing studies of which indicated that an estimated maximum size was 1700 mm FL ( Motomura, 2004b). The holotype (IPPS 08-01, 670 mm SL) was a mature female.