Akysis meridionalis, Ng, Heok Hee & Siebert, Darrell J., 2004

Ng, Heok Hee & Siebert, Darrell J., 2004, A new species of the catfish genus Akysis (Siluriformes: Akysidae) from southern Borneo, Zootaxa 733, pp. 1-8 : 2-6

Akysis meridionalis sp. nov. ( Fig. 1 )

Type material. Holotype: MZB 6102, 31.4 mm SL; Indonesia, Kalimantan Tengah (Borneo); Barito River drainage, Sungai Laung at Dessa Maruwei (0º21.986’S 114º44.103’E); D. J. Siebert, A. Tjakrawidjaja & O. Crimmen, 15­18 July 1992.

Paratype: BMNH 1998.9.30.18, 30.9 mm SL; data as for holotype.

Diagnosis. Akysis meridionalis is distinguished from all congeners by the following combination of characters: upper jaw projects more strongly forward, premaxillary teeth exposed when the mouth is closed; head width 18.2–19.4 % SL, body depth at anus 10.7– 11.5 % SL, depth of caudal peduncle 6.5–6.7 % SL, interorbital distance 32–34 % HL, length of maxillary barbels 104–110 % HL; 5 teeth on posterior edge of pectoral spine, and a colour pattern of a dark background with light patches ( Fig. 1 ).

Description. Head depressed and broad; body moderately compressed and relatively elongate. Mouth conspicuously subterminal; tip of snout noticeably protruding in front of apex of lower jaw ( Fig. 2 a). Dorsal profile rising evenly from tip of snout to origin of dorsal fin, then sloping gently ventrally to end of caudal peduncle. Ventral profile horizontal to origin of anal, then sloping dorsally to end of caudal peduncle. Head covered with small tubercles, body with tubercles arranged in 5–6 longitudinal rows on each side. Relatively large anterior and posterior nostrils, situated closely together and separated only by base of nasal barbel. Cranial fontanel not reaching base of supraoccipital process. Supraoccipital process narrow, its tip tapering and reaching predorsal plate. Premaxillary tooth plates exposed when mouth is closed. Dorsal origin nearer tip of snout than caudal flexure. Pectoral spine stout, with 5 (2) large serrae posteriorly. Anal origin posterior to adipose origin. Depressed dorsal not reaching adipose fin. Caudal fin strongly forked with pointed lobes.

Proportional measurements. In % SL: head length 26.5–29.0, head width 18.2– 19.4, predorsal distance 35.6–38.5, preanal length 62.1–63.4, prepelvic length 44.0–45.2, prepectoral length 25.6–27.4, body depth at anus 10.7–11.5, length of caudal peduncle 21.3–22.0, depth of caudal peduncle 6.5–6.7, pectoral­spine length 14.9–18.2, pectoral­fin length 22.3–25.2, length of dorsal­fin base 10.8–12.0, pelvic­fin length 12.3–13.7, length of anal­fin base 11.7–14.3, caudal­fin length 22.7–25.8, length of adipose­fin base 9.7– 13.1. In % HL: snout length 34–37, interorbital distance 32–34, eye diameter 10, length of nasal barbel 36–40, length of maxillary barbel 104–110, length of inner mandibular barbel 39–46, length of outer mandibular barbel 59–62.

Counts. Branchiostegal rays 7 (2). Gill rakers 1+6 (1). Vertebrae 11+23=34 (1) or 12+22=34 (1). Fin ray counts: dorsal I,4,i (2); pectoral I,6,i (2); pelvic i,5 (2); anal ii,7 (2); caudal 7/8 (2).

Coloration. Dorsal surface and sides of head and body dark brown; anterior and posterior nostrils rimmed with white; a white spot at base of maxillary barbel. Belly, chest and ventral surface of head white. Ventral surface of body posterior to belly white with scattered melanophores. A white spot on side of body between the dorsal and adipose fins; a white saddle mark on caudal peduncle posterior to adipose fin. Basal two­thirds of dorsal fin brown, remaining one­third hyaline. Anal­fin ray hyaline, but with a series of brown spots forming a stripe at about one­third of anal fin height from base. Pectoral and pelvic fins hyaline. Adipose fin with white spot at sub­anterior upper margin. Caudal fin brown with tips of lobes hyaline; a large hyaline spot at base of upper and lower lobe.

Distribution. Presently known only from the Barito River drainage of southern Borneo.

Etymology. From the Latin meridionalis , meaning southern, in reference to the known distribution of this species (southern Borneo); used as a noun in apposition.

Ng & Kottelat (1998) recognised two species groups within Akysis . Members of the A. pseudobagarius species group can be identified by a conspicuously subterminal mouth, relatively large and closely set narial openings, and deeply forked caudal fin. The snout clearly overhangs the lower jaw in this group and the projection of the snout beyond the apex of the lower jaw is supported by bones of the upper jaw. With a conspicuously subterminal mouth, large anterior and posterior narial openings separated only by the base of the nasal barbel, relatively elongate body and strongly forked caudal fin, A. meridionalis clearly belongs to the A. pseudobagarius species group as defined by Ng & Kottelat (1998).

Akysis meridionalis shares the southern part of the geographic range of Akysis with the following members of the pseudobagaruis ­group: A. pseudobagarius Roberts, 1989 ; A. alfredi Ng & Kottelat, 1998 ; A. baramensis Fowler, 1905 ; A. fuscus Ng & Kottelat, 1998 ; and A. macronema Bleeker, 1860 . Differences between it and the other southern members of the A. pseudobagarius species group are summarised in Table 1 . Akysis meridionalis resembles A. pseudobagarius in overall physiogamy but can be distinguished from it by fewer serrae on the inner edge of the pectoral spine (5 vs. 8–9; Roberts, 1989), depth of caudal peduncle (6.5–6.7 %SL vs. 3.5–5.5) and a wider head (18.2–19.4 %SL vs. 16.6– 17.8) with more widely set eyes (interorbital distance 32–34 %HL vs. 20–32). The snout of A. meridionalis is much more produced than that of A. baramensis ( Fig. 2 ). The largely exposed­when­mouth­is­closed premaxillary tooth plates of A. meridionalis separate it from A. alfredi (partially exposed; contra Ng & Kottelat, 1998), A. fuscus (not exposed, Ng & Kottelat, 1996), and A. macronema (not exposed, Tan & Ng, 2000); it can be further distinguished from A. alfredi and A. fuscus by a narrower head (18.2–19.4 %SL vs. 20.3–25.0 21.1–26.2 respectivelly). Akysis meridionalis also has a wider head (18.2–19.4 %SL vs. 20.3–21.0) than A. macronema .

The colour pattern of A. meridionalis is unique among southern memberts of the A. pseudobagarius species group but can be characterised as intermediate between that found in A. baramensis and A. fuscus , both of which are dark brown without any light patches or bands, and that found in A. alfredi , A. macronema , and A. pseudobagraius , all of which have a light background with dark brown patches or bands. Akysis meridionalis has a dark brown background colouration with white patches, the reverse of the colour pattern known for A. alfredi , A. macronema , and A. pseudobagarius .

Figures

FIGURE 1. Akysis meridionalis, MZB 6102, holotype, 31.4 mm SL; Borneo: Barito River basin. Dorsal, lateral and ventral views.

FIGURE 2. Ventral view of head of: a. A. meridionalis, MZB 6102, holotype, 31.4 mm SL; b. A. baramensis, ANSP 88950, paratype, 36.3 mm SL.

Tables

TABLE 1. Tabulation of diagnostic features distinguishing A. meridionalis from southern members of the A. pseudobagarius species group. Head width, body depth at anus, and caudal peduncle depth are % SL; interorbital distance and maxillary barbel length are % HL.

	N; size range (mm)	Head width	Interorbital distance	Maxillary barbel length	Body depth at anus
A. meridionalis	2; 30.9–31.4	18.2–19.4	32–34	104–110	10.7–11.5
A. pseudobagarius	4; 21.4–48.2	16.6–17.8	20–32	71–100	9.3–11.1
A. alfredi	26; 23.5–30.0	20.3–25.0	34–39	122–144	11.3–14.7
A. fuscus	13; 22.2–28.8	21.1–26.2	31–42	121–146	11.3–16.1
A. baramensis	10; 30.2–39.4	17.6–20.1	29–36	58–104	9.8–11.3
A. macronema	5; 30.9–31.4	20.3–21.0	32–38	110–137	8.3–13.0