Microsynodontis batesii Boulenger, 1903

Heok Hee Ng, 2004, The Microsynodontis (Teleostei: Siluriformes: Mochokidae) of the lower Guinea region, west central Africa, with the description of eight new species., Zootaxa 531, pp. 1-52: 3-9

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Microsynodontis batesii Boulenger, 1903


Microsynodontis batesii Boulenger, 1903  ZBK 

(Fig. 1)

Microsynodontis batesii Boulenger, 1903  ZBK  : 26, Pl. 4 (type locality: Mvile River, south Cameroon); 1905: 50; 1911: 476, Fig. 356; Holly, 1930: 257 (in part); Monod, 1928: 202; Pellegrin, 1929a: 359; 1929b: 452; Howes, 1980: 168.

Material. AMNH 232091 (1), female: 34.6 mm SL; Gabon: Ivindo River drainage, Minkebe gold camp forest, 1°43'38.2"N 12°48'35.8"E. BMNH 1903.7.28.105-110 (6), 3 syntype females: 48.8-58.3 mm SL, 3 syntype males: 75.7-84.7 mm SL; Cameroon: Mvile River. CAS 115547 (1), male: 37.7 mm SL; Cameroon: Mvila River drainage, Menyoo River, Ebolowa, 2°53'N 11°9'E. CAS 147487 (2), unsexed: 18.5 mm SL; Cameroon: Ntem or Campo River drainage, Mfiande and Seng Rivers. CAS 155689 (1), male: 57.8 mm SL; Cameroon: Ntem River drainage, Mboto River at Assok, 74 km SE of Ebolowa, 2°34'N 11°30'E. CAS 155691 (4), 2 females: 52.8-53.4 mm SL; 2 males: 65.5- 66.0 mm SL; Cameroon: Ntem River drainage, Mboto River at Mékomo, 37 km E of Ebolowa, 2°37'N 11°22'E. CU 80445 (1), male: 48.0 mm SL; Gabon: Woleu-Ntem province, “Bouth” creek where it crosses road from Bitam -Minvoul, 2°15'N 11°39'E. CU 80748 (8), males: 20.3-35.4 mm SL; Gabon: Woleu-Ntem province, “Deghe” creek near Auberge d’Ayengbe, 2°17'N 11°33'E. MCZ 32521 (1), female: 59.4 mm SL; Cameroon: Nyong River. MRAC 93-085-P-0279-0280 (2); females, 28.2-42.6 mm SL; Cameroon: Mboro River (tributary of Ntem River) at Akonekyé, 2°28'N 11°10'E. MRAC 93-108-P- 0651-0655 (5), 3 females: 21.5-26.5 mm SL; 2 males: 27.0-29.8 mm SL; Cameroon: Mengounou River, tributary of Mboua River, in Bilizi between Befio and Ekowong, 2°32'N 12°11'E. MRAC 93-108-P-0656 (1), male: 24.9 mm SL; Cameroon: river located 4 km from Akobass in the direction of Bitche, 2°22'N 12°4'E. MRAC 93-108-P-0657 (1), male: 22.8 mm SL; Cameroon: river after Aboulou in the direction of Mebang, 2°19'N 12°4'E. MRAC 93-108-P-0658 (1), male: 21.0 mm SL; Cameroon: Yété River, tributary of Kom River after Mebasa and before Ngoudjieng, 2°29'N 12°13'E. MRAC 93-108-P- 0659 (1), male: 28.2 mm SL; Cameroon: Milolo River, tributary of Kom River between Esaminkou and Andoung, 2°27'N 12°20'E. MRAC 94-028-P-0002 (1), male: 34.4 mm SL; Cameroon: Anga’a River, approximately 10 km from Yaoundé, 3°52'N 11°31'E. MRAC 95-030-P-1443-1448 (6), 1 female: 27.0 mm SL, 5 unsexed: 17.4-21.2 mm SL; Cameroon: first river at confluence at Mvangan, towards Nélefoup, 2°39'N 11°44'E. MRAC 95-030-P-1443-1448 (4), 17.4-27.0 mm SL, Cameroon: Mvong River, tributary of Kong River, 2°48'N 11°39'E. MRAC 95-030-P-1453-1454 (2), 1 male: 26.0 mm SL; 1 unsexed: 17.3 mm SL; Cameroon: Otobewo’o River, tributary of Woo River, between Ekombité and Nkolenyeng, 2°40'N 11°46'E. RMNH 34859 (8), 6 females: 36.1-65.6 mm SL; 2 males: 49.2-74.8 mm SL; Cameroon: Lobé River, waterfalls 9 km S of Kribi.

Diagnosis. Microsynodontis batesii  ZBK  is the largest known species of Microsynodontis  ZBK  , reaching a size of ca. 100 mm SL (the largest specimen among all other congeners is only ca. 65 mm SL). It can be distinguished from all congeners except M. hirsutus  ZBK  , M. laevigatus  ZBK  and M. polli  ZBK  in having a longer adipose fin (34.4-41.6% SL vs. 21.3-34.5). It differs from M. hirsutus  ZBK  in having in having a gently curved (vs. straight) dorsal spine (Fig. 2) and short (vs. long) tubercles on the dorsal and lateral surfaces of the head (Fig. 3), from M. laevigatus  ZBK  in having a serrated (vs. smooth) anterior edge of the pectoral spine (Fig. 4), rounded (vs. truncate) caudal fin (Fig. 9), and more slender caudal peduncle (5.8-9.2% SL vs. 9.3-11.4), and from M. polli  ZBK  (n=9) in having a shorter caudal fin (20.3-27.7% SL vs. 29.6-41.6).

Description. Biometric and meristic data as in Table 1. Body compressed. Predorsal profile gently convex; postdorsal body sloping gently ventrally. Preanal profile horizontal. Anus and urogenital openings located at vertical through middle of pelvic fin. Skin smooth. Lateral line complete and midlateral.

Head depressed and broad, broadly rounded when viewed laterally and with rounded snout margin when viewed from above. Gill openings narrow, extending from immediately ventral to posttemporal to immediately ventral to base of pectoral spine. Gill membranes united to, and attached across, isthmus. Bony elements of dorsal surface of head covered with thin skin. Nuchal shield large and terminating posteriorly with two rounded processes on each side. Supracleithral process thin and extending just short of vertical through posteriormost tip of nuchal shield.

Barbels in three pairs. Maxillary barbel long and slender, extending to just beyond base of last pectoral-fin ray. Inner mandibular-barbel origin close to midline, extending to base of pectoral spine and with 2 short, thin branches on anterior half and 3-5 long, thin branches on posterior half. Outer mandibular barbel originates posterolateral of inner mandibular barbel, extending to middle of pectoral-fin base and with 3-5 long, thin branches.

Eye ovoid, horizontal axis longest; located entirely in dorsal half of head. Orbit without free margin.

Mouth inferior and crescent-shaped; lips plicate. Oral teeth in rows on all tooth-bearing surfaces. Premaxillae narrow, with narrow ventral shelf and partially exposed when mouth closed. Primary teeth 10-15, conical and separated from secondary teeth by distinct gap. Secondary teeth 40-85, acutely pointed and recurved; disposed in 3-4 rows. Tertiary teeth 17-29, elongate, villiform and extending over full width of premaxillae. Dentary teeth 17-28, acutely pointed, strongly recurved and broader than secondary teeth; disposed in one or two transverse bands.

Dorsal fin located at anterior third of body, with convex margin and II,6 (39) or II,7 (3) rays. Dorsal-fin spine long, stout and slightly curved; smooth on both anterior and posterior margins. Adipose fin long, extending for most of postdorsal distance; margin slightly convex for entire length and posterior end deeply incised. Caudal fin rounded, with i,6,5,i (26) or i,6,6,i (16) principal rays. Procurrent rays symmetrical and extend only slightly anterior to fin base. Anal-fin base located ventral to posterior half of adipose fin. Anal fin with iv,7 (30); iv,8 (9); iv,9 (2) or iv,10 (1) rays and convex margin. Pelvic-fin origin at vertical ventral to posterior end of dorsal-fin base. Pelvic fin with i,6 (42) rays and slightly convex margin; tip of appressed fin not reaching anal-fin origin. Pectoral fin with I,5,i (13); I,6 (28) or I,6,i (1) rays; spine slightly curved and stout (Fig. 4f). Anterior spine margin with 22-33 small serrations along entire length of spine; serrations antrorse (distally directed) on distal two-thirds and anteriorly directed on proximal third. Posterior spine margin with 6-14 strong serrations along entire length. Pectoral-fin margin convex posteriorly. Vertebrae 13+22=35 (6); 11+25=36 (1); 12+24=36 (4); 13+23=36 (3); 14+22=36 (2); 12+25=37 (5); 13+24=37 (4); 12+26=38 (2); 13+25=38 (7) or 14+23=37 (1).

Males with numerous tubercles on sides of head on region extending from snout to preopercle, and long genital papilla situated immediately posterior to anus. Females with fewer tubercles on sides of head, and with smaller, distally flattened genital papilla.

Coloration. In 70% ethanol (adults larger than ca. 35 mm SL): dorsal and lateral surfaces and of head and body medium brown, fading to cream or light grayish brown on ventral third of body, belly (with large faint brown spots), and ventral surface of head (Fig. 1a). Snout with a series of cream spots delineating anterior and posterior nares, sometimes coalescing to form cream band running from anterior orbital margin to tip of snout. Cheek region with one or two cream spots immediately ventral to orbit. Cream band encircling nape at supraoccipital. Dorsal third of body with series of four cream vertical bar-shaped marks extending beyond lateral midline of body: first at middle of dorsal-fin base, second at adipose-fin origin, third at middle of adipose-fin base and last on caudal peduncle immediately posterior to adipose fin, sometimes encircling caudal peduncle as cream band. Ventral third of flanks with a longitudinal series of five to seven cream spots or vertical bar-shaped marks. Dorsal-, pectoral-, pelvic- and anal-fin rays with brown spots arranged in two or three bands. Caudal-fin rays with brown spots arranged in four bands and hyaline interradial membranes. Live coloration similar, with the addition of a faint dark reticulate pattern overlying the body (Fig. 1b).

Coloration of juveniles (smaller than ca. 35 mm SL) similar, except for more prominent brown spotting on ventral surfaces, and larger cream markings that sometimes assume more vermiform shapes, partially coalescing to form reticulate pattern (Fig. 1c). Pectoral fins hyaline, with scattered brown spots. Dorsal, anal and caudal fin with brown spots arranged in transverse bands.

Distribution. Known from the Ntem River drainage in southern Cameroon and northern Gabon, as well as the Campo, Ivindo, Lobé, Nyong and Sanaga River drainages in southern and central Cameroon (Fig. 5).

Remarks. Although M. batesii  ZBK  appears to have a much wider distribution compared to all other Microsynodontis  ZBK  from lower Guinea (Figs. 5, 7 & 13), it is possible that more than one species is involved in what is recognized as M. batesii  ZBK  here. In particular, the populations from the northernmost extent of its distribution (i.e. from the Nyong and Sanaga River drainages) should be further studied to verify their conspecificity with the material from southern Cameroon and northern Gabon, but the paucity of relevant material available for study does not allow for more a more conclusive test of this hypothesis.