Mystus
impluviatus. A New Species of Bagrid Catfish
(Teleostei: Bagridae) from Eastern Borneo
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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
peduncle.
THE genus 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
(ZRC).
DESCRIPTION
Mystus impluviatus n. sp. Figures 1, 2A, 3A, 4A,
and 5A
Holotype.—CAS 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 1982.
Paratypes.—CAS 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. |
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Diagnosis.—Mystus
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 peduncle).
Fig. 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.
Description.—Head 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.
Fig. 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.
 Fig.
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 = 1).
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)
% SL
Head Length |
27.3–29.2 (28.1
± 0.70) |
| Head width |
18.4–20.7 (19.4 ±
0.74) |
| Head depth |
1.60–20.4 (17.6 ±
1.30) |
| Predorsal length |
42.3–47.0 (38.7 ±
0.60) |
| Preanal length |
69.8–73.1 (71.7 ±
1.87) |
| Prepelvic length |
48.8–56.7 (51.4 ±
2.37) |
| Prepectoral length |
23.8-28-9 (26.3 ±
1.60) |
| Body depth at anus |
13.9–22.7 (18.2 ±
3.30) |
Length of caudal peduncle
|
16.6–19.7 (18.2 ±
1.18) |
| Depth of caudal peduncle |
7.7–10.0 (9.1 ±
1.08) |
| Pectoral spine length |
17.7–22.2 (19.5 ±
1.25) |
| Pectoral fin length |
18.8–23.6 (21.7 ±
1.80) |
| Dorsal spine length |
10.5–14.7 (12.4 ±
1.30) |
Length of dorsal fin base
|
14.4–17.2 (16.1 ±
0.92) |
| Pelvic fin length |
16.1–19.0 (17.2 ±
0.90) |
| Length of anal fin base |
9.3–13.5 (12.3 ±
1.09) |
| Caudal fin length |
26.9–34.4 (29.7 ±
2.18) |
| Length of adipose fin base |
31.6–36.1 (34.2 ±
1.46) |
| Maximum height of adipose fin |
4.7–6.0 (5.6 ±
0.34) |
| Post-adipose distance |
12.7–14.4 (13.4 ±
0.51) |
| % HL |
|
Snout length
|
33.0–36.1 (34.9 ±
1.34) |
| Interorbital distance |
33.3–40.0 (36.3 ±
2.21) |
| Eye diameter |
18.9–21.1 (20.9 ±
1.09) |
| Nasal barbel length |
64.9–86.9 (74.2 ±
8.32) |
| Maxillary barbel length |
372.5–424.6 (394.5 ±
21.12) |
| Inner mandibular barbel length |
96.2–121.8 (107.6 ±
8.16) |
| Outer mandibular barbel length |
148.7–191.5 (176.2 ±
11.56) |
Fig. 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 in
apposition.
DISCUSSION
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 fin base).
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.
COMPARATIVE MATERIAL
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, Muara Klingi.
ACKNOWLEDGMENTS
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.
LITERATURE CITED
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———. 2001. Clarias microstomus, a new species
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———. 2002. The identity of Mystus nigriceps (Valenciennes
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———, AND J. J. DODSON. 1999. Morphological and
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———, AND P. K. L. NG. 2001. A revision of the
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———, AND H. H. TAN. 1999. The fishes of the Endau
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FISH DIVISION, MUSEUM OF ZOOLOGY, UNIVERSITY OF MICHIGAN, 1109 GEDDES
AVENUE, ANN ARBOR, MICHIGAN 48109-1079. E-mail: heokheen@umich.edu.
Submitted: 6 Oct. 2002. Accepted: 6 Nov. 2002. Section editor: D.
G. Buth. |
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