Hemibagrus filamentus (Fang & Chaux, 1949 )

Ng, Heok Hee & Kottelat, Maurice, 2013, Revision Of The Asian Catfish Genus Hemibagrus Bleeker, 1862 (Teleostei: Siluriformes: Bagridae), Raffles Bulletin of Zoology 61 (1), pp. 205-291 : 238-239

Hemibagrus filamentus (Fang & Chaux, 1949)

( Fig. 24 )

Macrones filamentus Fang & Chaux , in Chaux & Fang, 1949: 200, Fig. 4 (type locality: Cambodia).

Mystus filamentus - Lim et al., 1996: 382; Rainboth 1996: 144, Pl. 19 Fig. 147.

Hemibagrus filamentus - Ng & Rainboth, 1999: 555, Fig. 1 ; Gaanantkul et al., 2000: 34; Kottelat, 2001b: 122, Fig. 327; Ferraris, 2007: 88; Vidthayanon, 2008: 114; Rainboth et al., 2012: 72, Plate 45, Fig. 943.

Material examined. — LAOS: CMK 13252, 6 ex., 54.7–186.2 mm SL, Vientiane province: confluence of Nam Leuk and Nam Ngong, 18°22'4"N 103°5'27"E ; CMK 13357, 1 ex., 159.4 mm SL, Vientiane province, Houay Sala Yai, a tributary of Nam San , 18°35'17"N 103°5'0"E ; CMK 13393, 9 ex., 63.2–129.3 mm SL, Vientiane province, Nam San downstream of Ban Pa Man , 18°32'3"N 102°55'48"E ; UMMZ 238567 , 30 ex., 62.0–138.0 mm SL, Vientiane province: Nam Tou, 8 km upstream from confluence with Nam Ngum reservoir ; UMMZ 238677 , 8 ex., 44.0–66.0 mm SL, Vientiane province: Nam Ngao at S end of Nam Ngum reservoir ; UMMZ 240634 , 12 ex., 50.0– 144.5 mm SL, Vientiane province: Nam Ti at junction with Nam Ngum and upstream 100 m ; NRM 15013, 1 ex., 236.8 mm SL, Sedone River, Pakse , 14°9'N 105°50'E ; NRM 15019, 1 ex., 198.5 mm SL ; NRM 15020, 1 ex., 191.9 mm SL ; NRM 15022, 1 ex., 251.6 mm SL, Laos .

CAMBODIA: MNHN 1966–728 , holotype, 419.8 mm SL, Cambodia ; UMMZ 232423 , 3 ex., 68.7–102.1 mm SL, Siem Reap: floating village at mouth of Siem Reap River, Mekong drainage (13°16'N 103°48'E) ; UMMZ 232462 , 1 ex., 150.6 mm SL, Siem Reap: fish trap W of floating village at mouth of Siem Reap River, Mekong drainage, 13°16'N 103°46'E ; UMMZ 232698 , 5 ex., 151.8–175.1 mm SL, Kompong Chhnang morning market, Mekong drainage .

Diagnosis. — Hemibagrus filamentus is distinguished from H. capitulum in having a longer, narrower head (head width 55–60% HL vs. 59–70), from H. fortis in having a shorter, deeper adipose fin (maximum height of adipose fin 2.3–3.2 times in the length of its base vs. 2.8–4.9) and the anteriormost branch of dorsal-fin rays longer than other branches (vs. branches of the dorsal-fin rays of almost equal length.) giving the dorsal fin a jagged (vs. rounded) distal margin ( Fig. 20 ), and from H. hoevenii in having the premaxillary tooth band not (vs. partially) exposed when the mouth is closed, rounded (vs. tapering) caudal-fin lobes, absence (vs. presence) of a broad and conspicuous dark margin around the caudal fin, a rounded (vs. triangular) anal fin, broader membranes of the dorsal fin which give it a rounded (vs. triangular) appearance, and filamentous extensions on the dorsal fin not reaching beyond middle of adipose-fin base (vs. very long filamentous extensions of the first two dorsalfin rays that reach beyond the posterior base of the adipose fin). It differs from H. nemurus in having a relatively longer and narrower head (head width 55–60% HL vs. 60–69) and a smaller dorsal to adipose distance (7.7–10.9% SL vs. 10.2–16.2), and from H. spilopterus in having a smaller dorsal to adipose distance (7.7–10.9% SL vs. 10.8–17.6), a flat (vs. gently convex) interorbital space, and dorsal-fin rays (excluding filamentous extensions) reaching beyond (vs. not reaching or just reaching) the adipose-fin origin.

Description. — Biometric and meristic data as in Table 13. General description as for genus. Head depressed and broad, body moderately compressed; head width 55–60% HL. Interorbital space flat. Eye diameter 10–15% HL. Premaxillary tooth band not exposed when mouth is closed. Dorsal profile rising evenly but not steeply from tip of snout to origin of dorsal fin, then sloping gently ventrally from there to end of caudal peduncle. Ventral profile horizontal to origin of anal fin, then sloping dorsally to end of caudal peduncle. Adipose-fin base short, approximately as long as anal-fin base; maximum height 5.0–7.2% SL (2.3–3.2 times in length of adipose-fin base). Adipose-fin origin separated from base of last dorsal-fin ray by distance of 7.7–10.9% SL. Dorsal spine stout, with 6–10 serrations along posterior edge. Anteriormost branch of each dorsal-fin ray longer than other branches, imparting jagged distal margin to fin; membranes broad, imparting rounded appearance. Adpressed dorsal fin (excluding filamentous extensions of rays) reaching beyond adipose-fin origin; filamentous extensions not reaching beyond middle of adipose-fin base. Pectoral spine stout, with 13–18 large serrations along posterior edge. Anal fin rounded, origin slightly posterior to adipose origin. Caudal fin forked; upper and lower lobes rounded. Maxillary barbels reaching barbels reaching at least vertical through base of last anal-fin ray (221–265% HL). Maximum recorded size 420 mm SL.

Colour. — Dorsal surface of head and body uniform brownish-grey; ventral surface of head and body dirty white; adipose fin brownish-grey, without black spot; fin-rays and inter-radial membranes of all fins grey; dorsal surface of barbels brownish-grey, ventral surface dirty white.

Distribution. — Hemibagrus filamentus is known from the middle and lower Mekong in Laos, Thailand and Cambodia ( Fig. 22 ).

Habitat and biology. — Hemibagrus filamentus is found in slow-flowing or standing waters, moving into flooded forests during periods of high water levels. It feeds on crustaceans and fishes ( Rainboth, 1996).

Figures

Fig. 24. Hemibagrus filamentus, CMK 13393, 110.2 mm SL, Laos: Nam San.

Fig. 4. Hemibagrus sabanus, ZRC 40493, 104.9 mm SL, Borneo: Sabah, Segama River.

Fig. 1. Method of measurements used in this study: 1, Standard length; 2, Predorsal length; 3, Preanal length; 4, Prepelvic length; 5, Prepectoral length; 6, Dorsal-spine length; 7, Dorsal-fin length; 8, Length of dorsal-fin base; 9, Length of anal-fin base; 10, Pelvic-fin length; 11, Pectoral-fin length; 12, Pectoral-spine length; 13, Caudal-fin length; 14, Length of adipose-fin base; 15, Maximum height of adipose fin; 16, Dorsal to adipose distance; 17, Post-adipose distance; 18, Length of caudal peduncle; 19, Depth of caudal peduncle; 20, Body depth at anus; 21, Head length; 22, Head width; 23, Head depth; 24, Snout length; 25, Interorbital distance; 26, Eye diameter.

Fig. 20. Schematic illustrations of fully extended dorsal fins of members of the H. nemurus species group: a, H. fortis, ZRC 40522, 126.9 mm SL; b, other members of the H. nemurus species group (H. nemurus, ZRC 39181, 132.4 mm SL, illustrated). Scale bar = 10 mm.

Fig.22. Map showing collection localities of Hemibagrus nemurus, H. capitulum and H. filamentus specimens examined in this study.