Rita macracanthus, Heok Hee Ng, 2004

Heok Hee Ng, 2004, Rita macracanthus, a new riverine catfish (Teleostei: Bagridae) from South Asia., Zootaxa 568, pp. 1-12 : 2-8

Rita macracanthus sp. nov.

(Fig. 1)

Pimeladus [sic] rita (non Hamilton, 1822) - McClelland, 1842: 575.

Rita buchanani (non Bleeker, 1853) - Day, 1877: 454, Pl. 103 Fig. 1, Pl. 104 Fig. 2 (in part); Day, 1880: 231; Day, 1889: 165, Fig. 60 (in part).

Rita rita (non Hamilton, 1822) - Zugmayer, 1913: 24; Khan, 1934: 661; Ahmad, 1943: 326; Sufi, 1957: 221; Qureshi, 1965: 43, Fig. 109 (in part); Jayaram, 1966: 440 (in part); Islam and Siddiqi, 1971: 38; Mirza, 1972: 179; Husain, 1973: 321; Mirza, 1973: 254; Mirza and Kashmiri, 1973: 180; Ahmad and Khan, 1974: 126; Mirza, 1974: 79; Mirza and Ahmad, 1974: 101; Ahmad et al., 1976: 243; Misra, 1976: 118, Fig. 22 (in part); Mirza, 1976: 117; Jayaram, 1977: 40 (in part); Coad, 1981: 15; Mirza and Omer, 1984: 87; Butt, 1986: 30; Mirza and Ahmad, 1987: 261; Qureshi et al., 1988: 184; Khan et al., 1991: 24; Talwar and Jhingran, 1991: 578, Fig. 192 (in part); Mirza and Jan, 1993: 20; Afzal et al., 1995: 137; Mirza and Bhatti, 1995: 27; Iqbal et al., 1997: 56; Jayaram, 1999: 227 (in part); Mirza, 2000: 356; Mirza and Alam, 2002: 33; Mirza, 2003: 17.

Type material. Holotype: UMMZ 237502 , 262.8 mm SL, male; Pakistan: Indus River at Attock ; L. Roe, 1988.

Paratypes: MCZ 22186 , 2 ex., 228.7 mm SL, female, 271.1 mm SL, male; Pakistan: Punjab, Chenab River ; M. M. Carleton, 1872. RMNH 8795 , female, 243.7 mm SL; Pakistan: Lahore ; F. Day, date unknown.

Diagnosis. Rita macracanthus differs from R. chrysea , R. gogra and R. kuturnee in having relatively small eyes (6.9-8.7% HL vs. 14.3-29.2) set further apart (interorbital distance 39.4-44.1% HL vs. 28.7-37.9). It further differs from R. gogra in having the dorsal surface of the head between the eyes and supraoccipital covered with thin skin (vs. a thick layer of muscle), from R. kuturnee in having moderately elongate vomerine tooth patches with rounded, peg-like teeth (vs. very narrow patches with villiform teeth), from R. chrysea in having a granulated anterior margin of the dorsal spine (vs. middle third with large serrations) and from R. sacerdotum in having a long dorsal spine that reaches to the middle of the adipose fin (vs. short spine not reaching the origin of the adipose fin). Rita macracanthus can also be distinguished from both R. chrysea and R. sacerdotum in having the vomerine teeth in two distinct lateral patches (vs. a single median patch).

Rita macracanthus resembles R. rita very closely, but can be distinguished from it in having, in specimens greater than 100 mm SL, a longer dorsal (reaching to middle of adipose-fin base when appressed vs. to origin of adipose-fin base; 37.2-45.5% SL vs. 25.6- 41.7) spine, a longer pectoral spine [reaching to three-quarters (vs. to less than half) the distance between tip of cleithral process and pelvic-fin origin; 28.7-30.0% SL vs. 22.1- 25.5], a more slender caudal peduncle (7.6-8.4% SL vs. 8.2-10.7), and a shorter premaxillary tooth band in which the maximum width is 4.8-6.4 (vs. 3.1-4.5) times its maximum length (Fig. 2).

Description. Morphometric data as given in Table 1. Head slightly depressed; dorsal profile slightly convex posteriorly and ventral profile almost straight. Bony elements of dorsal surface of head covered with thin skin; bones readily visible, ornamented with numerous small tubercles. Eye ovoid, horizontal axis longest; located entirely in dorsal half of head. Orbit with free margin. Gill openings wide, extending from posttemporal to beyond isthmus. Gill membranes free from isthmus, with 6 branchiostegal rays. First branchial arch with 4+9 gill rakers.

Mouth subterminal, fleshy upper lip extending anteriorly beyond upper jaw. Oral teeth small, of two kinds, in irregular rows on all tooth-bearing surfaces. Premaxillary tooth band rounded, of equal width throughout, with villiform teeth. Dentary tooth band much narrower than premaxillary tooth band at symphysis, becoming slightly wider before tapering again posterolaterally; teeth on anterior quarter villiform; those on posterior three-quarters bluntly rounded, peg-like. Vomerine tooth patches somewhat elliptical, paired, along lateral margins of palate; teeth on first to sixth anteriormost rows somewhat villiform, those on rest of tooth patch bluntly rounded, peg-like.

Barbels in three pairs. Maxillary barbel short and slender, not extending beyond opercle. Nasal barbel slender, extending to halfway between its base and anterior margin of orbit. Mandibular-barbel origin close to midline; barbel thicker and longer than nasal barbel, extending to three-quarters of distance between its base and base of pectoral spine.

Body slightly compressed, becoming more so towards 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 horizontal to anal-fin base, then sloping gently dorsally from there to end of caudal peduncle. Skin smooth. Lateral line complete and midlateral in position. Anterior and cephalic canal pores ramifying in asymmetric pattern in humeral region and dorsal surface of head respectively. Vertebrae 14+20=34, 15+19=34 or 16+19=35 (holotype: 14+20=34).

Dorsal fin located above middle of body; origin nearer tip of snout than caudal flexure; with 6 rays. Dorsal-fin margin convex, usually with anterior branch of fin-rays longer than other branches.. Dorsal-fin spine long, straight and robust; spine extending to middle of adipose fin (distal tip of spine damaged in holotype). Anterior margin of spine produced into sharp keel; lateral and posterior surfaces smooth.

Pectoral fin with stout spine, sharply pointed at tip, and 9 or 10 (holotype: 9) rays. Anterior spine margin with 32-42 strong serrations along entire length; posterior spine margin with 28-31 strong serrations along entire length (spine is broken near the base in holotype). Pectoral-fin margin straight anteriorly, convex posteriorly.

Pelvic-fin origin at vertical through posterior end of dorsal-fin base. Pelvic fin with i,7 rays and slightly convex margin; tip of appressed fin not reaching anal-fin origin. Anus and urogenital openings located at vertical through middle of appressed pelvic fin.

Adipose fin with convex margin for entire length; posterior end deeply incised. Analfin base ventral to posterior half of adipose fin. Fin with iv,8-10 (holotype: iv,9) rays and slightly curved margin.

Caudal peduncle moderately slender. Caudal fin deeply forked, with i,7,7,i or i,7,8,i (holotype: i,7,8,i) principal rays; upper and lower lobes pointed (caudal fin damaged in holotype). Procurrent rays symmetrical, extending only slightly anterior to fin base.

Coloration. In 70% alcohol: brown on dorsal region and upper half of flank, gradually fading to dark yellow on lower two-thirds of flank and ventral region. Base of dorsal fin brown, base of pectoral, pelvic and anal fins dark yellow, other parts of all fins yellow. Proximal quarter of barbels brown, distal three-quarters dirty white.

Distribution. Known from the Indus River drainage in Afghanistan, Pakistan and northwestern India.

Etymology. From the Greek makros, meaning long, and akantha, meaning thorn, in reference to the relatively long dorsal and pectoral spines of this species. Used as a noun.

Biology. According to Khan (1934), R. macracanthus (as R. rita ) feeds on invertebrates and small fishes. Males have branched and comb-like testes and in the Jhelum River (a tributary of the Indus River), breeding season lasts from June to the end of July, during which the fish migrates to colder waters in shoals.

Discussion

Rita macracanthus and R. rita are very similar-looking species (both species would key out as R. rita using Ferraris, 1999), so the possibility that the differences outlined in this study are solely due to ontogeny must be ruled out. A bivariate analysis (ANCOVA) of the pectoral-spine length, dorsal-spine length and caudal peduncle depth against SL (Fig. 3) shows that the differences are not solely ontogenetic, as the regression lines are significantly different (P<0.00001, P=0.03706 and P=0.01658 respectively).

The shapes of the tooth plates in catfishes are known to undergo ontogenetic changes, especially those on the palate. In R. rita , as in many other catfishes, the palatal tooth plates tend to fuse along their medial margins in large specimens, giving the appearance of one large median tooth plate. However, the premaxillary tooth plate appears to undergo little ontogenetic change in shape. It was not possible to measure the premaxillary toothplates of all of the specimens of R. rita and R. macracanthus in this study without seriously damaging them (due to the condition they were preserved in), but those for which accurate measurements were possible support the utility of the premaxillary tooth plate morphology as a diagnostic character for the two species; the relationship between the premaxillary width:length ratio against size (SL) is significantly different for the two species (t=2.573, P=0.0422; Fig. 4).

The fauna of the Indus River drainage is poorly studied. It is likely that many of the freshwater fish species currently thought to occur in both the Indus and Ganges River drainages are separate (one Indus and one Gangetic) species, as noted in Sperata by Mirza (2003). Prior to the collision of the Indian subcontinent with Asia, the paleo-Indus River was more west-flowing and formed part of a larger twin river system (much like that of the Ganges-Brahmaputra system today) with the west-flowing paleo-Ganges on the southern edge of the Asian continent. The collision of India and the subsequent tectonic uplift caused both the Indus to become more south-flowing, and the Ganges to switch from a west- to an east-lowing river system, linking with the Brahmaputra River in the process (Qayyum et al., 1997). The possibility of this being the vicariant event that led to the allopatric speciation of R. macracanthus and R. rita should be further investigated.