Pimelodus cavasius Hamilton, 1822 Bagrus cavasius Macrones cavasius Mystus cavasius Mystus (Mystus) cavasius Mystus mukherjii Ganguly & Datta, 1975 The identity of catfishes identified as Mystus cavasius (Hamilton, 1822) (Teleostei: Bagridae), with a description of a new species from Myanmar. Prosanta Chakrabarty Heok Hee Ng Zootaxa 2005 1093 1 24 45FTL Bagridae Mystus CoL Animalia Siluriformes 2 Chordata species cavasius  (Fig. 1)   Pimelodus cavasius Hamilton, 1822: 203, Pl. XI Fig. 67 [type locality: "Fluvio Atterei" (=Atrai River)]  Bagrus cavasiusValenciennes, in Cuvier & Valenciennes, 1840: 409; Jacquemont, 1835-1844: Pl. XIV Fig. 2; Bleeker, 1854: 113.  Macrones cavasius Guenther, 1864: 76 (in part); Day, 1877: 447, Pl. C Fig. 1 (in part); Day, 1889: 155 (in part); Jenkins, 1910: 140.  Mystus cavasiusShaw & Shebbeare, 1937: 91, Fig. 90, Pl. 3 Fig. 3; Chauhan, 1947: 276; Chauhan & Ramakrishna, 1953: 411; Motwani et al., 1962: 21; Bhuiyan, 1964: 63; Singh, 1964: 89; Qureshi, 1965: 42, Fig. 106; Babu Rao & Chattopadhyay, 1969: 887, Pl. 2 Fig. 1; Rahman, 1974: 2, Fig. 1G; Pillai & Yazdani, 1977: 5; Jayaram, 1977: 29, Fig. 21A (in part); Jayaram & Singh, 1977: 262; Jayaram, 1981: 196, Fig. 92A (in part); Shrestha, 1981: 155, Fig. 73; Dutt et al., 1982: 27 (in part); Sharma & Dutt, 1983: 334 (in part); Husain & Tilak, 1984: 275; Sen, 1985: 136, Fig. 74; Edds, 1986a: 5; Edds, 1986b: 17; Sharma & Rajput, 1986: 566; Barman, 1988: 49; Datta Munshi & Srivastava, 1988: 235, Pl. XXIX Fig. 2; Rahman, 1989: 200; Roberts, 1989: 124 (in part); Talwar & Jhingran, 1991: 559, Fig. 184 (in part); Sen, 1992: 180, Fig. 58; Dutta et al., 1993: 25; Roberts, 1994: 248 (in part); Shrestha, 1994: 52, Fig. 79; Sen, 1995: 561, Pl. XXVI Fig. 2; Husain, 1997: 595; Jayaram, 1999: 235, Fig. 118C (in part); Menon, 1999: 200 (in part); Nath & Dey, 2000: 89, Fig. 78, Pl. 2-12; Barman, 2002: 263, Fig. 66; Jayaram & Anuradha Sanyal, 2003: 46, Fig. 5 (in part); Mishra et al., 2003: 26.  Mystus (Mystus) cavasiusJayaram, 1954: 532, Fig. 2 (in part); Motwani & David, 1957: 11; Majumdar, 1958: 368; Srivastava, 1968: 71, Fig. 45; Misra, 1976: 87, Fig. 18 (in part); Gupta, 1985: 17, Pl. IB.  Mystus mukherjii Ganguly & Datta, 1975: 293, Figs. 1-2 (type locality: Subarnarekha River, below waterfalls at Hundru, Ranchi District, Bihar, India).  Material examined.  BMNH1860.3.19.955, 113 mm SL; India(photograph examined).  BMNH1938.2.22.122 (1), 121.8 mm SL;  BMNH1938.2.22.124-128 (5), 57.8-71.5 mm SL; India: Bombay Presidency, Deolali district [=Maharashtra, Nasik district], Darna River.  BMNH1938.2.22.123 (1), 108.9 mm SL; India: Bombay Presidency, Deolali district [=Maharashtra, Nasik district], Unanda River.  CAS94220 (1), 80.7 mm SL; India: Orissa, Rushukulya River near Purushotampur, 15-20 km inland.  CAS50327 (32), 160.5- 67.4 mm SL; Nepal: ChitawanValley, Dudara River, tributary to Rapti River.  OSUS15972 (2), 57.4-68.0 mm SL; Nepal: Sunsari, Sapt Kosi River, bought in market in Itahari.  OSUS17352 (1), 75.2 mm SL; Nepal: Nawalparasi, Narayani River at Taadi Ghat.  OSUS17434 (2), 75.5-77.9 mm SL; Nepal: Nawalparasi/Chitawan, Narayani River below Rapti River confluence.  UMMZ189647 (2), 84.6-88.0 mm SL; India: West Bengal, Santal Parganas, Kanloi River near Kotalpukur Railway Station.  UMMZ208686 (1), 63.7 mm SL; Bangladesh, Sylhet, Surma (Meghna) drainage, Shari River, 6.8 km S of Jaintapur on Sylhet-Shillong highway.  UMMZ208750 (10), 59.3-96.5 mm SL; Bangladesh: Sylhet, Surma (Meghna) drainage, Gowain River and Khal at Gowainghat.  UMMZ238800 (5), 130.1-152.4 mm SL; India: West Bengal, market in Calcutta.  UMMZ244745 (2), 97.9-103.9 mm SL; India: West Bengal, Mansai River, 1 km after Amtala on JalpaiguriCoochbehar road, 26°19'30"N 84°14'4"E.  UMMZ244869 (2), 90.1-90.2 mm SL; India: West Bengal, Tista River at Tista Barrage, 26°45'1"N 88°35'11"E.  UMMZ244939 (1), 100.3 mm SL; India: West BengalHooghly River at Kalna, 23°13'30"N 88°22'39"E.  USNM205615 (2 paratypesof M. mukherjii), 76.3-77.3 mm SL; India: Bihar, Ranchi district, Subarnarekha River, below waterfalls at Hundru.  Diagnosis. Mystus cavasiusdiffers from other congeners with a long-based adipose fin (except M. seengteeand M. falcarius) in having a combination of a black spot in front of the dorsal-spine base, a dark humeral mark, a body without distinct midlateral stripes, very long maxillary barbels reaching to caudal-fin base, dorsal spine short and feebly serrate, tall dorsal fin, and 13-22 gill rakers. Mystus cavasiusdiffers from M. seengteein having fewer gill rakers on the first gill arch (13-22 vs. 23-28; Table 1) and a more gently sloping predorsal profile (making an angle of 20-25° with the horizontal vs. 30-35°; Fig. 2), and from M. falcariusin having fewer rakers on the first gill arch (13-22 vs. 22-29; Table 1), a straight or gently concave (vs. markedly concave) dorsoposterior margin of the dorsal fin (Fig. 3), a faint (vs. very prominent) dark spot at the base of the dorsal spine and a ovoid (vs. crescentic) dark humeral mark.  Description. Biometric data are given in Table 2. Head depressed; dorsal profile evenly sloping (at angle of 20-25° to horizontal) and ventral profile almost straight. Bony elements of dorsal surface of head covered with thin skin; bones readily visible, especially on posterior half of neurocranium, and ornamented with numerous fine, radial grooves. Anterior cranial fontanelle extending from behind snout to line through posterior orbital margins, separated from posterior fontanelle by narrow epiphyseal bar. Posterior fontanelle extending to base of supraoccipital spine. Supraoccipital spine elongate, slender and with blunt tip; extending to anterior nuchal plate. Eye ovoid, horizontal axis longest; located entirely in dorsal half of head. Gill openings wide, extending from exposed surface of posttemporal to beyond isthmus at line through mouth corners. Gill membranes free from isthmus. First branchial arch with 13-22 long, slender gill rakers. Mouth subterminal, fleshy upper lip extending anteriorly beyond upper jaw. Oral teeth small and villiform, 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. Barbels in four pairs. Maxillary barbel long and slender, extending to caudal-fin base. Nasal barbel slender, extending to vertical through base of pectoral spine. Inner mandibular-barbel origin close to midline; thicker and longer than nasal barbel and extending to base of posteriormost pectoral-fin ray. Outer mandibular barbel originating posterolateral of inner mandibular barbel, extending to vertical through middle of dorsal-fin base.  Body moderately compressed. 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 21+17=38 (2), 20+19=39 (1), 21+18=39 (5), 22+17=39 (2), 21+19=40 (9), 22+18=40 (10), 21+20=41 (3), 22+19=41 (4), 23+18=41 (1), 21+21=42 (1) or 22+21=43 (1). Dorsal fin with spinelet, spine, and 6 (1) or 7 (38) rays. Origin of dorsal fin anterior to mid-body, about two-fifths of body. Dorsal fin margin straight or slightly concave, with first two fin rays longer than others. Dorsal fin spine moderately long, straight and slender, posterior edge with 3-4 indistinct serrations. Serrations fewer, lower and less distinct in smaller specimens. Anterior nuchal plate acutely triangular. Pectoral fin with stout spine, sharply pointed at tip, and 6 (1), 7 (5), 8 (21), 9 (9) or 10 (3) rays. Anterior spine margin smooth; posterior spine margin with 12-22 serrations along entire length (serrations fewer in smaller specimens). Pectoral fin margin straight anteriorly, convex posteriorly. Postcleithral (humeral) process short and slender, with concave dorsal edge and extending to anterior tip of anterior nuchal plate. Pelvic fin origin at vertical through posterior end of dorsal-fin base, with i,5 (39) 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 short genital papilla reaching to base of first anal-fin ray. Adipose fin with very long base and deeply incised posterior portion, spanning almost all of postdorsal distance. Anal fin origin located at approximately middle third of adipose fin, fin with iv,6 (7), iv,7 (20), iv,8 (10) or iv,9 (2) rays and curved posterior margin. Caudal peduncle moderately deep. Caudal fin deeply forked, with i,6,6,i (1), i,6,7,i (6), i,6,8,i (2), i,7,7,i (18) or i,7,8,i (12) principal rays; upper lobe slender and lanceolate, lower lobe pointed. Procurrent rays extending only slightly anterior to fin base. Coloration. In 70% ethanol: dorsal surface of head and body uniform brownish gray in some individuals, silvery white in others. Dark spots in front of base of dorsal spine and on humeral region, faint in some specimens. Some individuals with distinct dark stripe along lateral line, consisting of densely aggregated melanophores and with pale stripe without melanophores immediately above. Ventral surfaces of head and body dirty white; adipose fin brownish gray. All fins hyaline, with melanophores on fin membranes on some individuals, usually more densely aggregated along margins with fin rays. Dorsal half of barbels gray dorsally, gradually turning to dirty white on ventral half and tips.  Distribution. Known from the Ganges, Brahmaputra, Mahanadi, Subarnarekhar and Godavari river drainages in northern India, Nepal and Bangladesh (Fig. 4). Records of M. cavasiusfrom the Indus River drainage further to the west presumably refer to this species, but no material for verification was available to us.  Habitat and biology. Mystus cavasiusis known from a wide variety of habitats, including both fast- and slow-flowing rivers and streams (Nath & Dey, 2000), where it reportedly feeds on invertebrates and, to a smaller extent, smaller fishes (Bhatt, 1971). In the Ganges, this species spawns in August and September (Bhatt, 1971). 923892679 Bangladesh 923892687 India Ranchi District, Bihar 923892668 India 923892680 India Bombay Presidency, Deolali District [=maharashtra, Nasik District] 923892673 India Bombay Presidency, Deolali District [=maharashtra, Nasik District] 923892678 India Bombay Presidency, Deolali District [=maharashtra, Nasik District] 923892677 India Orissa 923892669 Nepal Chitawan 923892671 Nepal Sunsari 923892670 Nepal Nawalparasi 923892681 Nepal Nawalparasi / Chitawan 923892672 India West Bengal 923892686 Bangladesh Sylhet 923892684 Bangladesh Sylhet 923892676 India West Bengal 923892683 India West Bengal 923892685 India West Bengal 923892690 India West Bengal 923892691 India Bihar, Ranchi District