Encheloclarias baculum Ng & Lim, 1993

Tan, Heok Hui, Sukri, Rahayu Sukmaria, Kahar, Rafhiah & Dommain, René, 2023, First record of Encheloclarias (Teleostei: Clariidae) from Brunei Darussalam with notes on the taxonomic status of E. baculum Ng & Lim, 1993, and E. prolatus Ng & Lim, 1993, Raffles Bulletin of Zoology 71, pp. 237-247 : 238-245

Encheloclarias baculum Ng & Lim, 1993

( Figs. 1–8 )

Encheloclarias baculum Ng & Lim, 1993: 27 ; Ng & Tan, 2000: 538 (listed as comparative material); Parenti & Lim, 2005: 192; Tan & Ng, 2005: 83; Ferraris, 2007: 149; Ng, 2012: 116 (listed as comparative material); Sule et al., 2016: 429 (table).

Encheloclarias prolatus Ng & Lim, 1993: 29 ; Ng & Tan, 2000: 539 (listed as comparative material); Ferraris, 2007: 150; Ng, 2012: 116 (listed as comparative material); Sule et al., 2016: 429 (table).

Material examined. - BMNH 1863.12.11:162 , 1 ex., 57.1 mm SL, holotype; West Kalimantan: Sambas (photographs and radiograph only; see Fig. 2 ) . --- ZRC 63175 , 1 ex., 75.0 mm SL; Brunei Darussalam: Belait District: Belait river basin; Badas peat dome, Badas ; in a tip pool; Dommain R. & Zulkiflee R., 19–21 August 2022 . --- ZRC 63817 , 2 ex., 67.9–82.0 mm SL, 2 ex., 70.0–82.0 mm SL; Brunei Darussalam: Belait District: Belait river basin; Badas peat dome, Badas ; in shallow water pools; Dommain R., Cobb A., Incham, J. M. & Zulkiflee R., 11–12 February 2023 . --- ZRC 63818 , 2 ex., 64.4–102.5 mm SL, ZRC 63819 , 1 ex., 79.2 mm SL, ZRC 63820 , 1 ex., 116.0 mm SL; Brunei Darussalam: Belait District: Belait river basin; Mendaram peat dome ; in shallow water pools; Dommain R., Incham, J. M. & Zulkiflee R., 17–18 February 2023 . --- ZRC 44215 , 2 ex., 104.8–110.7 mm SL; Sarawak: Sibu, Sungei Kemayan peat swamps; Yong D., October 1998 . --- ZRC 39748 , 1 ex., 50.3 mm SL; Sarawak: Serian, peat swamp ca. 11 km into Gedong road ; H. H. Tan & S. H. Tan, 16 January 1996 . --- ZRC 56630 , 2 ex., 67.3–69.5 mm SL; ZRC 56631 , 1 ex., 54.1 mm SL; Sarawak: Kuching, Matang peat swamps ; local fisher, 10 November 2017 . --- ZRC 63516 , 5 ex., 122.8–154.3 mm SL; Sarawak: Kuching ; local fisher, December 2017 .

Diagnosis. Enchelolarias baculum can be differentiated from its congeners in having the following unique combination of characters: Anal and caudal fins confluent at their bases, fusion with caudal fin at times fully to ¾; highest number of caudal vertebrae amongst its congeners (45–50 vs. 34–45); long and slender body; 8–10 gill rakers; 3–5 serrae on posterior edge of pectoral-fin spine; dorsal-fin rays 25–29 (mode 26); anal-fin rays 53–65 (mode 56).

Description. Selected meristic and morphometric data listed in Table 1; see Figs. 1–8 for general body form. Body long, slender, cylindrical, gently tapering towards caudal peduncle. Dorsal profile rising gently from tip of snout to origin of dorsal fin, and thereafter straight to end of caudal peduncle, except gently convex along adipose fin. Ventral profile of head slightly convex, thereafter almost horizontal to end of caudal peduncle. Skin smooth. Lateral line complete and midlateral in position. Vertebrae 15–17 + 45–50 = 60–67 (n = 8).

Head relatively acutely depressed; predorsal profile slightly convex, ventral profile straight. Bony elements of dorsal surface of head covered with smooth, velvety skin; bones not readily visible. Frontal fontanelle longitudinally ovoid; located in interorbital region, with anterior tip reaching imaginary line connecting anterior margin of orbits. Occipital fontanelle ovoid; located at base of occipital process, slightly narrower than frontal fontanelle, posterior edge reaches imaginary line connecting base of pectoral-fin spines. Occipital process, broad, with rounded point. Eye ovoid, horizontal axis longest, subcutaneous; located dorsolaterally on head. Gill openings narrow, extending from dorsalmost point of the pectoral-fin base to isthmus. Gill membranes free from each other, only united across isthmus, with 9 branchiostegal rays. First branchial arch with 8–10 gill rakers (n = 6).

Mouth subterminal, with fleshy, plicate lips. Barbels in four pairs; long and slender with thick fleshy bases. Maxillary barbel typically longest and thickest at base, length 132–159% HL. Nasal barbel longer than inner mandibular barbel, length 94–149% HL. Inner mandibular barbel origin close to midline; length 89–121% HL. Outer mandibular barbel originating posterolateral of inner mandibular barbel, longer than inner mandibular barbel, length 99–143% HL. Anterior nostril at tip of long tube; tube extending beyond edge of mouth when directed anteriorly. Posterior nostril just anterior to eye, at base of nasal barbel, opening about eye diameter.

Dorsal fin with moderately short base, spanning middle onethird of body; with 25–29 (mode 26) rays covered by thick layer of skin and without spine. Dorsal-fin pterygiophore insertion at 9 th to 12 th vertebrae (mode 10, n = 6). Dorsal-fin margin relatively straight, parallel to dorsal edge of body. Adipose fin with gently convex dorsal margin; anterior point of origin contacting base of last dorsal-fin ray, gently curving posteriorly to fuse broadly with upper procurrent caudal fin rays. Anal-fin base long, with 53–65 (mode 56) rays, covered by thick layer of skin; margin straight, parallel to ventral edge of body. Anal-fin origin at vertical through seventh dorsal-fin ray, pterygiophore insertion at 15 th to 18 th vertebrae (mode 17, n = 6); confluent with caudal fin base, sometimes fully fused to ¾. Caudal fin long and rounded or truncate, with 15 fin rays, anterior-lowermost procurrent caudal ray longer than last few anal-fin rays.

Pectoral fin broad, abruptly and sharply pointed at tip, with I,8 rays. Anterior margin of spine smooth; posterior margin of spine serrated, with 3–5 (mode 3) inward directed serrae (n = 8). Pectoral-fin margin weakly convex anteriorly, gently convex posteriorly. Pelvic-fin origin at vertical through base of third to fourth dorsal-fin ray, pterygiophore insertion at 13 th to 16 th vertebrae (mode 14 or 15, n = 6), with i,6 rays and convex margin; tip of fin reaching base of second analfin ray. Anus and urogenital openings located at vertical through middle of pelvic fin.

Preserved colouration. See Figs. 2–6 . Overall colour of the Brunei specimen is black to dark purple ( Sarawak material appear dark brown to grey) on dorsum to lateral, fading to brownish-purple on venter. Unpaired fins uniformly black, except for areas with recovery from damage, which is hyaline or grey. Paired fins light grey to hyaline. Posterior margin of opercle pale brown. Specimens from Sarawak have similar colouration.

Live colouration. See Figs. 7–8 . Overall colour of both Brunei and Sarawak populations is dark brownish-purple. Area behind eye and opercular region brighter reddish-brown. Barbels brown proximally, lightening to white distally. Pectoral and pelvic fins lighter brown. Adipose fin uniform dark brown. Caudal fin lighter brown. Both dorsal and anal fins with proximal one-third dark brown, distal portion lighter brown. Lateral line pattern on body appearing as an interrupted white line.

juveniles and maintained in captivity for a few months. The habitat was revisited in May 2008 but was badly disturbed and used as a city dump.

Specimens obtained from Matang peat swamps near Kuching ( Sarawak) were obtained via bait angling by hobbyists in 2017. Encheloclarias baculum was not the main target fish, as they were angling for Channa spp. The habitats in this area were remnant patches of peat swamp forest, which had been more extensive in the past.

Field biology notes. The first specimen of Encheloclarias baculum from Brunei (ZRC 63175) was obtained in a bottle trap, placed over two nights (19–21 August 2022) in a tip-up pool within Shorea albida peat swamp forest on the Badas peat dome (see Fig. 9 ). A tip-up pool forms by uprooting of a falling tree. The uprooting creates a pit in the waterlogged peat swamp forest floor, which quickly fills with water ( Dommain et al., 2015). Tip-up pools are some of the most permanent aquatic habitats on peat domes where water is continuously flowing to the peat dome margin, and the peat surface may dry out periodically during periods without rain ( Cobb et al., 2017). The tip-up pool from which Encheloclarias was collected had the following dimensions and abiotic parameters — size: 2.3 m × 1.0 m; water depth: 15 cm; water temperature 26.1°C; pH 3.9 (readings taken on 27 May 2022); and a dissolved O 2 concentration of 2.56 mg /L (2 June 2022). Syntopic fishes included Rasbora kottelati (Danionidae) , Ompok borneensis (Siluridae) , Clarias leiacanthus , and C. nieuhofii (Clariidae) .

In the pristine Mendaram peat swamp forest, Encheloclarias baculum was collected from very shallow pools (6–8 cm water depth) with pH 3.7–3.9 and dissolved O 2 concentrations of 2.4–2.9 mg /L (readings on 18 February 2023), but not found in tip-up pools with more than 28 cm water depth. Syntopic species were Rasbora kottelati and Clarias nieuhofii .

A juvenile specimen of Encheloclarias baculum (ZRC 39748) was obtained from a flooded peat swamp at Gedong ( Sarawak), in ca. 10–20 cm water depth amongst submerged leaf litter and peat deposits. During a survey in January 1996, many specimens of Betta brownorum were also obtained along with other syntopic species (see Tan & Ng, 2005: 83). A subsequent trip in August of the same year yielded only Betta ibanorum , from deeper waters. Another follow up trip in June 1998 was attempted, but the forest had been clear felled and drained, and no fish were obtained (Tan HH, pers. obs.).

Two specimens of Encheloclarias baculum from Kemayan peat swamps near Sibu ( Sarawak) were obtained from a kind donation in 1998. These were caught using a hand net as Distribution. For details on the type locality of Encheloclarias baculum , please refer to Ng & Lim (1993). Encheloclarias baculum is recorded to date from Sambas (West Kalimantan), southern part of Sarawak (Kuching to Sibu) and Brunei (Belait area, Badas peat dome). This is the most widespread species currently known.

See Fig. 10 for distribution of all known species of Encheloclarias . The genus Encheloclarias is restricted to coastal peat swamp forests and freshwater swamp forest habitats within Southeast Asia. Only E. velatus and E. kelioides were found in syntopy in Jambi, however this is likely to be an artefact of sampling, as they were obtained from a food market, and very likely to have been sourced from nearby peat swamp habitats and pooled together for sale (pers. obs.).

Comparative notes. Encheloclarias baculum can be further differentiated from its congener E. tapeinopterus by the greater number of gill rakers on the first arch (8–10 vs. 6), greater number of anal-fin rays (53–65 vs. 50), smaller pre-dorsal fin length (27–33% SL vs. 34; 80–103% HL vs. 131), larger dorsal-fin length (30–34% SL vs. 26), smaller inner mandibular barbel length (89–121% HL vs. 141); from Encheloclarias curtisoma in the greater number of anal-fin rays (53–65 vs. 47–50), smaller head width (11–14% SL vs. 15–17), smaller body width (5–11% SL vs. 13–14), smaller body depth (7–11% SL vs. 13–15); from Encheloclarias kelioides in the greater number of gill rakers on the first arch (8–10 vs. 7); from Encheloclarias velatus by having fewer serrae along the posterior edge of the pectoral-fin spine (3–5 vs. 9–12); and from Encheloclarias medialis in having fewer serrae along the posterior edge of the pectoral-fin spine (3–5, vs. 2) and fewer gill rakers on the first arch (8–10 vs. 7).

Comments. The specimens from Matang in Sarawak (ZRC 56631), Gedong (ZRC 39748) and Kemayan (ZRC 44215) were initially keyed out to E. baculum , and Matang (ZRC 56630) to E. prolatus based mainly on the observable extent of confluence between anal and caudal fins — a major morphological character differentiating E. baculum from E. prolatus . This initial identification was perplexing as it suggested that either both species were syntopic or misidentified. Adding to this initial confusion, both these taxa were described based on single poorly preserved specimens, both collected in the late 1800s. Ng & Lim (1993: 28–29) already noted the similarities between E. baculum and E. prolatus , but without access to a series of fresh specimens, they concluded that each was a distinct species. The extent

RAFFLES BULLETIN OF ZOOLOGY 2023

of confluence between the anal and caudal fins has now been shown to be variable, ranging from nearly full fusion to around ¾ fusion.

Based on our examination of Encheloclarias baculum (eleven fresh specimens from Sarawak and Brunei), and the information on E. prolatus available from the original description ( Ng & Lim, 1993), we are unable to identify characters that would distinguish the two species. We conclude that both names apply to the same species and as first revisers select E. baculum as the valid name. Encheloclarias prolatus should be considered a junior synonym of E. baculum .

A preliminary search through the wet collection of vertebrate animals in the Sarawak Museum was conducted in December 2022 (Tan HH, pers. obs.). The holotype of E. prolatus could not be located and is most likely presumed lost .

This study highlights the challenges in clearing the identity and distribution of rare and uncommon taxa, whose descriptions are based on one, or very few specimens.

Figures

Fig. 1. Composite radiographs of Encheloclarias baculum (above), ZRC 63175, 75.0 mm SL, Brunei; and Heterobranchus longifilis (below), ZRC 38289, 119.4 mm SL, Africa. This composite shows the extension of neural spines into the adipose fin in Heterobranchus.

Fig. 2. Encheloclarias baculum, BMNH 1863.12.11:162, 57.1 mm SL, composite of dorsal, lateral and ventral views of holotype; West Kalimantan: Sambas (Photograph: NHM, London).

Fig. 3. Encheloclarias baculum, ZRC 63175, 75.0 mm SL; composite of dorsal, lateral and ventral views of a preserved specimen from Brunei (Photograph: THH).

Fig. 4. Encheloclarias baculum, ZRC 63817, 82.0 mm SL, composite of dorsal, lateral and ventral views; showing individual with fully confluent anal- and caudal-fins; Brunei: Badas (mirror inverted) (Photograph:THH).

Fig. 5. Encheloclarias baculum, ZRC 6630, 67.3 mm SL; composite of dorsal, lateral and ventral views of a preserved specimen from Sarawak (Kuching: Matang) (Photograph: THH).

Fig. 6. Encheloclarias baculum, ZRC 44215, 110.8 mm SL; composite of dorsal, lateral and ventral views of a preserved specimen from Sarawak (Sibu: Kemayan) (Photograph: THH).

Fig. 7. Encheloclarias baculum, ZRC 63817, 82.0 mm SL, live colouration (Brunei: Badas) (Photograph: THH).

Fig. 8. Encheloclarias baculum, ZRC 63516, 105.1 mm SL, live colouration (Sarawak: Matang). Note discolouration on body due to collection artefacts (Photograph: THH).

Fig. 9. Tip-up pool within Badas peat dome at Brunei, in which Encheloclarias baculum (ZRC 63175) was collected (Photograph: RD).

Fig. 10. Map showing the distribution of Encheloclarias: circle for E. tapeinopterus, hexagon for E. baculum, square for E. kelioides, heart for E. curtisoma, diamond for E. velatus, and star for E. medialis (each symbol may represent more than one location).