Mystus impluviatus. A New Species of
Bagrid Catfish (Teleostei: Bagridae) from Eastern Borneo
| Heok Hee Ng
new species of bagrid catfish in the
genus Mystus is described from the Mahakam River
drainage in eastern Borneo. Mystus impluviatus
closely resembles Mystus nigriceps and Mystus
castaneus but differs in having a second posterior
fontanel on the supraoccipital. It can be further distinguished
from M. nigriceps and M. castaneus a combination
of the following characters: maximum height of adipose fin
4.7–6.0% SL, length of adipose fin base 31.6–36.1%
SL, long second and third dorsal fin rays, causing the dorsal
fin to appear less rounded, maximum height of pectoral spine
serrations 3.6–4.8% of spine length, a deeply forked
caudal fin with a slender upper lobe, and a brown body with
a distinct dark triangular patch on the base of the caudal
Mystus Scopoli, 1777 is a group of bagrid catfishes
found in streams and rivers throughout South and Southeast
Asia. The genus Macrones was used by earlier authors,
but Macrones Duméril, 1856, is preoccupied
by Macrones Newman, 1841, in Coleoptera and
Mystus Scopoli, 1777, was revived by Fowler (1928)
as a replacement name. Mystus is poorly diagnosed
and is polyphyletic (Mo, 1991). Twentytwo of the 45 nominal
species of Mystus are found in Southeast Asia,
19 of which are currently considered valid.
The identity of Mystus nigriceps Valenciennes has
been the subject of much confusion among ichthyologists
(Ng, 2002). A recent study by Ng (2002) recognized two distinct
species in the material generally identified as M. nigriceps:
one in Java and the other in Sumatra, the Malay Peninsula,
and northern and western Borneo. Ng restricted M. nigriceps
for the Javanese species and described the other as Mystus
castaneus. While comparing M. castaneus and
material identified as M. nigriceps from Java and
the Mahakam River drainage in eastern Borneo, differences
were observed, which suggested that the Mahakam River material
belong to an undescribed species.
MATERIALS AND METHODS
Measurements were made point to point with dial calipers
and data recorded to tenths of a millimeter. Counts and
measurements were made on the left side of specimens whenever
possible. Sub units of the head are presented as proportions
of head length (HL). Head length itself and measurements
of body parts are given as proportions of standard length
(SL). Measurements follow those of Ng and Dodson (1999);
the maximum height of the pectoral spine serrations is measured
following Ng and Tan (1999). Institutional abbreviations
follow Leviton et al. (1985) except for the Zoological Reference
Collection of the Raffles Museum of
Biodiversity Research, National University of Singapore
Mystus impluviatus n. sp. Figures 1, 2A, 3A, 4A,
97049, male, 87.0 mm SL; Borneo: Kalimantan Timur, small
river on road 12.2 km from Sebulu crossroads towards forest
and 59 km from Air Putih crossroads (08169S, 117809E); M.
S. Christensen, H. Christensen, and H. Aschanuddin, 31 July
94621, 2 juveniles, 20.3–22.8 mm SL; Borneo: Kalimantan
Timur, beneath floating water hyacinth island about 6 m2,
flooded swamp forest ca. 6 km SE of Kota Bangun (0°16'S,
116°34'E); M. S. Christensen et al., 1983. CAS 95038,
4 males, 76.2–119.6 mm SL, 1 female 80.8 mm SL; USNM
371267, 1 male, 83.0 mm SL, 1 female, 81.1 mm SL; Borneo:
Kalimantan Timur, remnant pool in swamp forest, approximately
120 m2 along Sungai Kedang Kepala, ca. 15 km NNW of Muara
Kaman (0°9'S, 116°43,E); M. S. Christensen and M.
Schellenberg, November 1982. CAS 95035, 1 male, 98.9 mm
SL; 1 female, 113.0 mm SL; MZB 10703, 1 female, 96.1 mm
SL; Borneo: Kalimantan Timur, Belayan River (0°7'N,
116°22'E); M. S. Christensen et al., 10 August 1982.
CAS 97045, 3 juveniles, 25.7–30.0 mm SL; Borneo: Kalimantan
Timur, from small stream on logging trail going inland from
southern junction of Sebulu, side road to stream approximately
4 km (0°16'S,117°0'E); M.S. Christensen and G.von
Drabich, 31 October 1982.
Fig. 1. Mystus impluviatus, paratype
male, CAS 95035, 98.9 mm SL.
impluviatus differs from both M. castaneus and
M. nigriceps in having a second posterior fontanel
on the supraoccipital (Fig. 2). It further differs from M.
castaneus in having a shallower adipose fin (4.7–6.0%
SL vs 6.1– 7.0), smaller serrations on the posterior edge
of the pectoral spine (maximum height of serrations 3.6–4.8%
of spine length vs 6.9–8.0), and a more deeply forked
caudal fin with a more slender upper lobe (Fig. 3). Mystus impluviatus
further differs from M. nigriceps in having a longer adipose
fin base (31.6–36.1% SL vs 26.3– 31.4), longer second
and third dorsal fin rays, causing the dorsal fin to appear
less rounded, and a brown body with a distinct dark triangular
patch on the base of the caudal peduncle (vs greenish gray body
with a diffuse dark triangular patch on the base of the caudal
2. Schematic illustration
of dorsal views of heads of (A) Mystus impluviatus,
CAS 97049, holotype, 87.0 mm SL; (B) Mystus castaneus
and Mystus nigriceps (M. castaneus, UMMZ 155714,
77.9 mm SL illustrated), showing presence of second posterior
fontanel on supraoccipital in M. impluviatus. Scale
bar represents 10 mm.
depressed; dorsal profile slightly convex and ventral profile
almost straight. Bony elements of dorsal surface of head covered
with thin skin; bones readily visible, ornamented with numerous
fine grooves. Eye ovoid, horizontal axis longest, with free
margin; located entirely in dorsal half of head. Gill openings
wide, extending from posttemporal to beyond isthmus. Gill membranes
free from isthmus, with 9 (n 5 11) or 10 (n 5 4) branchiostegal
rays. First branchial arch with 6 + 14 (n = 4), 5 + 20 (n =
2), 5 + 21 (n = 2), 6 + 19 (n = 1), 6 + 20 (n = 4) or 6 + 21
(n = 2) gill rakers.
Mouth subterminal, fleshy upper lip extending anteriorly beyond
upper jaw. Oral teeth small and viliform, in irregular rows
on all tooth-bearing surfaces. Premaxillary tooth band rounded,
of equal width throughout. Dentary tooth band much narrower
than premaxillary tooth band at symphysis, tapering laterally.
Vomerine tooth band unpaired, continuous across midline; smoothly
arched along anterior margin, tapering laterally to point extending
posteriorly well past level of premaxillary band; band width
narrower than premaxillary band at midline, widening laterally
and then tapering to a sharp point posterolaterally.
3. Schematic illustration
of caudal fins of (A) Mystus impluviatus, CAS 95038,
paratype, 83.0 mm SL; (B) Mystus castaneus, UMMZ 155714,
77.9 mm SL. Scale bar represents 5 mm.
4. Map showing distribution of Mystus castaneus,
Mystus impluviatus and Mystus nigriceps (c). Base
map courtesy of W. J. Rainboth.
Barbels in four pairs. Maxillary barbel long and slender, extending
beyond caudal fin. Nasal barbel slender, extending to halfway
between posterior orbital margin and dorsalmost extent of gill
opening. Inner mandibular-barbel origin close to midline; barbel
thicker and longer than nasal barbel and extending just beyond
base of last pectoral fin ray. Outer mandibular barbel originates
posterolateral of inner mandibular barbel, extending to base
of first pelvic fin ray.
Body slightly compressed, becoming more so toward caudal peduncle.
Dorsal profile rising evenly but not steeply from tip of snout
to origin of dorsal fin and sloping gently ventrally from origin
of dorsal fin to end of caudal peduncle. Ventral profile slightly
convex to anal fin base, then sloping slightly dorsally to end
of caudal peduncle.
Skin smooth. Lateral line complete and midlateral in position.
Vertebrae 20 + 17 = 37 (n = 10), 21 + 16 = 37 (n = 1), 20 +
18 = 38 (n = 2), 21 + 17 = 38 (n = 1), or 20 + 19 = 39 (n =
Dorsal fin with spinelet, spine, and 6 (n = 2) or 7 (n = 13)
rays. Origin of dorsal fin slightly anterior to midline. Dorsal
fin margin convex, usually with anterior branch of fin rays
longer than other branches. Dorsal fin spine short, straight
and slender, posterior edge with low irregular serrations.
Pectoral fin with stout spine, sharply pointed at tip, and 8
(n = 4), 9 (n = 2) or 9,i (n = 9)
rays. Anterior spine margin smooth; posterior spine margin with
10–12 small serrations along entire length. Pectoral fin
margin straight anteriorly, convex posteriorly.
Pelvic fin origin at vertical through posterior end of dorsal-fin
base, with i,5 (n = 15) rays and slightly convex margin; tip
of adpressed fin not reaching anal fin origin. Anus and urogenital
openings located at vertical through middle of adpressed pelvic
fin. Males with a long, slender genital papilla extending to
base of second anal fin ray.
Adipose fin with convex margin for entire length; anterior end
reaching to base of last dorsal fin ray. Anal fin base ventral
to posterior half of adipose fin, with iv,7 (n = 2), iv,8 (n
= 9) or iv,9 (n = 4) rays and curved posterior margin.
Caudal peduncle moderately slender. Caudal fin deeply forked,
with i,7,7,i (n = 2) or i,7,8,i (n = 13) principal rays; upper
lobe slender and lanceolate, lower lobe pointed. Procurrent
rays extend only slightly anterior to fin base. Morphometric
data as in Table 1.
TABLE 1. MORPHOMETRIC DATA FOR
Mystus impluviatus (n = 10). Range
(mean ± SD)
||18.4–20.7 (19.4 ±
||1.60–20.4 (17.6 ±
||42.3–47.0 (38.7 ±
||69.8–73.1 (71.7 ±
||48.8–56.7 (51.4 ±
||23.8-28-9 (26.3 ±
|Body depth at anus
||13.9–22.7 (18.2 ±
|Length of caudal peduncle
|16.6–19.7 (18.2 ±
|Depth of caudal peduncle
|| 7.7–10.0 (9.1 ±
|Pectoral spine length
||17.7–22.2 (19.5 ±
|Pectoral fin length
||18.8–23.6 (21.7 ±
|Dorsal spine length
||10.5–14.7 (12.4 ±
|Length of dorsal fin base
|14.4–17.2 (16.1 ±
|Pelvic fin length
||16.1–19.0 (17.2 ±
|Length of anal fin base
|| 9.3–13.5 (12.3 ±
|Caudal fin length
||26.9–34.4 (29.7 ±
|Length of adipose fin base
||31.6–36.1 (34.2 ±
|Maximum height of adipose fin
|| 4.7–6.0 (5.6 ±
||12.7–14.4 (13.4 ±
|33.0–36.1 (34.9 ±
||33.3–40.0 (36.3 ±
||18.9–21.1 (20.9 ±
|Nasal barbel length
||64.9–86.9 (74.2 ±
|Maxillary barbel length
||372.5–424.6 (394.5 ±
|Inner mandibular barbel length
||96.2–121.8 (107.6 ±
|Outer mandibular barbel length
||148.7–191.5 (176.2 ±
5. (A) Maximum height of the adipose fin (%SL)
plotted against SL (mm) for Mystus castaneus and Mystus
impluviatus; (B) Length of the adipose fin base (%SL) plotted
against SL (mm) for M. impluviatus and Mystus nigriceps.
Color in alcohol.—Dorsal
surface of head and body uniform medium brown, with a very faint
dark gray humeral spot and a distinct oval or triangular dark
gray spot on base of caudal peduncle.Ventral surfaces of head
and body dirty white; adipose fin and fin rays of all fins brown;
interradial membranes of all fins with scattered melanophores.
Dorsal half of barbels brown at base, gradually turning to dark
yellow on ventral half and tips.
Distribution.—Known from the Mahakam
River drainage in eastern Borneo (Fig. 4).
Etymology.—From the Latin impluvium,
which refers to a skylight; in allusion to the second posterior
fontanel on the supraoccipital of this species. Used as a noun
The identity of M. nigriceps has been problematic (for
a detailed discussion, see Ng, 2002), particularly so for the
material from the Mahakam River. It has been variously identified
as M. nigriceps by Christensen (1992) and as M.
cf. cavasius by Kottelat (1994). Mystus impluviatus,
M. castaneus, and M. nigriceps can be distinguished
from all other Southeast Asian Mystus in having a moderately
long adipose fin (29–37% SL) and an oval or triangular
dark gray patch on the base of the caudal peduncle (all other
Southeast Asian Mystus lack markings on the base of
the caudal peduncle, except for M. bimaculatus Volz,
1904, which has a black vertical bar with a white vertical bar
immediately anterior to it at the base of the caudal peduncle).
The difference in the height of the adipose fin between M.
castaneus and M. impluviatus cannot be explained
by ontogenetic change alone, as a plot of the maximum height
of the adipose fin against SL (Fig. 5a) shows. A plot of the
length of the adipose fin base against SL (Fig. 5b) also shows
that ontogeny alone cannot explain the differences observed
between M. nigriceps and M. impluviatus. Lines
drawn through the plot of all data from both species as a single
series have very low r2-values (0.0002 for the maximum height
of the adipose fin and 0.0296 for the length of the adipose
Mystus impluviatus appears to be endemic to the Mahakam
River drainage (or, at least, to eastern Borneo). This is not
surprising, given that the Mahakam River was isolated from the
other main Southeast Asian river drainages throughout the low
sea level periods of the Pleistocene (Voris, 2000). Although
the endemism of the Mahakam fish fauna is currently thought
to be low (about 9%; Kottelat, 1994), recent studies have identified
at least three more endemic species of catfishes (e.g., Ng,
2000, 2001; Ng and Ng, 2001). Therefore, the fish fauna of the
Mahakam River deserves further study as it is likely that there
are more endemic species in the river system.
Mystus nigriceps: RMNH 2948, holotype, 119.3 mm SL;
RMNH 3009, 199, 99.4 mm SL; Java. RMNH 15857, 105.3 mm SL; Java:
Batavia (neotype of Bagrus micracanthus). MNHN 4369,
71.5 mm SL; Java (paralectotype of Bagrus keletius;
photograph examined). CMK 9214, 7 ex., 63.9– 77.0 mm SL;
Java: Java Timur, Kali Brantas basin, canal at Nggareman (Kecamatan
Patianrowo, Kabupaten Kertosono) (7°34'S, 112°5'E).
CMK 9231, 8 ex., 57.0–84.4 mm SL; Java: Java Timur, Kali
Brantas basin, channelized stream through drained (formerly
swampy) area at Campurdarat, S of Tulungagung (8°10'S, 111°20'E).
MZB 10032, 2 ex., 78.1–79.5 mm SL; Java: Java Timur, Kabupaten
Bojonegoro, Kecamatan Bojonegoro, Desa Bojonegoro, Bengawan
Solo. MZB 10056, 10 ex., 56.1–86.1 mm SL; Java: Java Timur,
Brantas River, Lengkong Dam at Mojokerto. MZB 10066, 4 ex.,
77.6–110.5 mm SL; Java: Ciujung River, Kecamatan Pamarayan
Serang. ZRC 43878, 4 ex., 67.5–81.0 mm SL; Java: Java
Tengah, Citalahab next to rice field, probably draining into
Citanduy about 20 km to Banjar.
Mystus castaneus: ZRC 41848, holotype, 121.4 mm SL;
Borneo: Sarawak, Serian market, from Sungai Sadong. ZRC 28176,
1 paratype, 77.6 mm SL; Malaysia: Johor, Kota Tinggi, Sungai
Mupor. ZRC 39419, 3 paratypes, 124.0–134.5 mm SL; Sarawk:
Serian market. ZRC 40487, 8 paratypes, 86.5–114.1 mm SL;
Borneo: Brunei, Tutong district, Sungai Merimbun, outflow from
Tasik Merimbun draining into Sungai Tutong. ZRC 40490, 6 paratypes,
92.7–143.8 mm SL; Borneo: Sarawak, Serian market. UMMZ
155689, 1 ex., 101.9 mm SL; UMMZ 155713, 1 ex., 58.7 mm SL;
UMMZ 155714, 6 ex., 38.8– 87.8 mm SL; Sumatra: Musi River,
I am grateful to D. Catania (CAS), M. Kottelat (CMK), I. Rachmatika,
and R. Hadiaty (MZB); M. van Oijen (RMNH), D. Nelson (UMMZ),
and K. Lim (ZRC) for access to material under their care, and
to W. Rainboth for permission to use the map of Southeast Asia.
This work was funded by support from the Rackham School of Graduate
Studies of the University of Michigan.
CHRISTENSEN, M. S. 1992. Investigations on the ecology and fish
fauna of the Mahakam river in east Kalimantan (Borneo), Indonesia.
Int. Rev. Ges. Hydrobiol. 77:593–608.
FOWLER, H. W. 1928. Further notes and descriptions of Bombay
shore fishes. J. Bombay Nat. Hist. Soc. 33:100–119.
KOTTELAT, M. 1994. The fishes of the Mahakam River, east Borneo:
an example of the limitations of zoogeographic analyses and
the need for extensive fish surveys in Indonesia. Trop. Biodiv.
LEVITON, A. E., R. H. GIBBS, JR., E. HEAL AND C. E. DAWSON.
1985. Standards in herpetology and ichthyology.
Part I. Standard symbolic codes for institutional resource collections
in herpetology and ichthyology. Copeia 1985:802–832.
MO, T.-P. 1991. Anatomy and systematics of Bagridae (Teleostei)
and siluroid phylogeny. Theses Zool. 17: 1–216.
NG, H. H. 2000. Bagrichthys vaillantii (Popta, 1906), a valid
species of bagrid catfish from eastern Borneo (Teleostei: Siluriformes).
Zool. Med. 73:327–332.
———. 2001. Clarias microstomus, a new species
of clariid catfish from eastern Borneo (Teleostei: Siluriformes).
Zool. Stud. 40:158–162.
———. 2002. The identity of Mystus nigriceps
(Valenciennes in Cuvier & Valenciennes, 1840), with the
description of a new bagrid catfish (Teleostei: Siluriformes)
from Southeast Asia. Raffles Bull. Zool 50:161–168.
———, AND J. J. DODSON. 1999. Morphological
and genetic descriptions of a new species of catfish,
Hemibagrus chrysops, from Sarawak, East Malaysia, with an assessment
of phylogenetic relationships (Teleostei: Bagridae). Ibid. 47:45–57.
———, AND P. K. L. NG. 2001. A revision of
the akysid catfish genus Acrochordonichthys Bleeker. J. Fish
———, AND H. H. TAN. 1999. The fishes of the
Endau drainage, Peninsular Malaysia with descriptions of two
new species of catfishes (Teleostei: Akysidae, Bagridae). Zool.
VORIS, H. K. 2000. Maps of Pleistocene sea levels in Southeast
Asia: shorelines, river systems and time durations. J. Biogeog.
FISH DIVISION, MUSEUM OF ZOOLOGY, UNIVERSITY OF MICHIGAN, 1109
GEDDES AVENUE, ANN ARBOR, MICHIGAN 48109-1079. E-mail: [email protected]
Submitted: 6 Oct. 2002. Accepted: 6 Nov. 2002. Section editor:
D. G. Buth.