Eirmotus octozona Schultz, 1959

Kottelat, Tan Heok Hui Maurice, 2008, Revision Of The Cyprinid Fish Genus Eirmotus, With Description Of Three New Species From Sumatra And Borneo, Raffles Bulletin of Zoology 56 (2), pp. 423-433 : 424-426

Eirmotus octozona Schultz, 1959

( Figs. 3a–b , 7a )

Eirmotus octozona Schultz, 1959: 11 ; Kottelat, 1989: 7; Kottelat et al., 1993: 35 (part).

Material examined. – USNM 177521 , holotype, 32.1 mm SL, Thailand: Bung Borapet (aquarium trade); H. Axelrod, 1957 .

Non-type material: ZRC 8385–8397 , 13 ex. , CMK 17456 , 3 ex. , 28.4–35.6 mm SL, Malaysia: from aquarium fish collectors in Johor; H. K. Lim, 1989 .

Diagnosis. – Eirmotus octozona is distinguished from the other species of Eirmotus by the following unique combination of characters: bar 1 present; a large and distinct black mark just anterior to anus, visible in lateral ( Fig. 7a ) and ventral views; simple dorsal-fin rays black, black pigment patch in some specimens extending onto first branched ray, other rays hyaline or in some specimens with diffused chromatophores on last dorsal-fin ray, adjacent to upper extremity of bar 6 ( Fig. 7a ); serrae on last simple dorsal-fin ray 25-31; pectoral fin with faint black margin along uppermost ray; width of bar 5 equal to 1-1½ lateral row scales; mouth terminal, lower jaw wide, anteriorly rounded.

Description. – See Fig. 3a–b for general body shape and Table 1 for meristics and morphometrics. Size up to 35.6 mm SL. Dorsal fin with 3 simple and 8–9½ branched rays; origin over lateral scale 5–7. Anal fin with 3 simple and 5–6½ branched rays; origin under lateral row scale 10–12. Pelvic fin with 1 simple and 8–9 branched rays; origin under lateral row scale 4–6. Lateral row scales 19–21; predorsal scales 6–7; transverse scales ½6–7½ between dorsal-fin and anal-fin origins, ½3½ on caudal peduncle.

Mouth terminal, upper lip not entirely visible in ventral view; lower jaw relatively wide, rounded anteriorly. No marked angle at articulation of lower jaw.

Colouration. – Preserved: Body yellowish-brown; markings dark brown to black. Bar 3 not reaching ventral midline, or only faint below opercle. One dot along dorsal midline between each bars 3 to 8; most prominent one between bars 5 and 6, at posterior extremity of dorsal-fin base. Bar 4 not reaching ventral mid-line but usually a spot on ventral midline at level of bar. Bar 5 usually not reaching pelvic-fin base, but a mark at base of pectoral fins, on proximal part of fins and between them. A conspicuous spot on ventral midline and extending upwards immediately in front of anus, about halfway between bars 5 and 6, aligned with spot at posterior extremity of dorsal-fin base. One faint dot along ventral midline between each bars 6 to 8. Axial streak distinct between bars 6 and 8. A longitudinal mark present in some specimens along lateral midline between bars 5 and 7, apparently more obvious in smallest specimens.

Fins hyaline. Dorsal fin with simple rays black, pigment patch in some specimens extending onto first branched ray, other rays hyaline or with diffused chromatophores on last one, adjacent to upper extremity of bar 6. Anterior rays of anal fin black at base, continuing bar 6. Base of pelvic-fin rays black.

In life, body translucent, light yellow-brown, marks black.

Distribution. – Schultz (1959) originally described E. octozona on the basis of aquarium specimens reportedly collected in Bung Borapet, a lake in an extensive swampy area about 300 km north of Bangkok, Thailand. The species has not been collected again in Thailand, despite the central plain of Thailand and especially Bung Borapet having been quite well sampled (e.g., Kaw-anantakul et al., 2003). Although it cannot be excluded that the species and/or its habitat have been overlooked, or that it became extirpated since, this locality seems erroneous ( Kottelat, 1982). We have examined specimens labelled as obtained by the aquarium trade in Johor, for which we could not obtain accurate locality data but which seem effectively to have been collected in western Malaysia; this could suggest that, if the types have really been obtained in Thailand, the type locality is more likely in peninsular Thailand. The absence of other records for the species is possibly due to lack of sampling in the correct habitat, or the destruction of the suitable habitat.

In 2006, we obtained information from an aquarium fish collector in Johor that the species was earlier collected in peat swamp forests of the area of Ayer Hitam. We had not asked about the presence of the species, but he spontaneously described a number of species previously collected for the aquarium trade in this area and which have not been collected since, despite numerous efforts. These species also included Gymnochanda filamentosa ( Ambassidae ), another species described from the Malay Peninsula but for which there is no precise locality data. Our search in that area did not yield any Eirmotus specimen. The peat swamp forests of this area have been severely impacted and are now much reduced in extant and in the diversity of existing microhabitats.

Comparative notes. – Eirmotus octozona is distinguished from E. isthmus by the following characters: a larger and more distinct black mark just anterior to anus (vs. small and diffused chromatophores); more serrae along posterior edge of last simple dorsal ray (25–31, vs. 22–26); higher mode of lateral scales (21 vs. 19); broader bars (width of bar 5 equal to 1–1½ lateral row scales, vs. ½ or less); shorter head (length 27.8–29.4 % SL, vs. 29.1–31.4); stouter caudal peduncle (depth 12.5–14.8 % SL, vs. 11.0–12.7); mouth terminal, lower jaw wide, anteriorly rounded (vs. subinferior, upper lip entirely distinct in ventral view, lower jaw pointed anteriorly).

Eirmotus octozona is distinguished from E. furvus in having: less distinct black mark on posterior tip of dorsal fin and rest of dorsal fin hyaline (vs. more distinct black mark and diffused chromatophores scattered on all rays); anterior rays of anal fin black at base (vs. simple rays entirely black, in adults); more serrae on last simple dorsal ray (25–31, vs. 17–21); bars narrower (width of bar 5 equal to 1–1½ lateral row scales, vs. 1½–2); shorter head (length 27.8–29.4 % SL, vs. 29.5–32.8); slightly greater prepelvic length (45.0–51.1 % SL, vs. 43.7–45.7).

Eirmotus octozona is distinguished from E. insignis in having: anterior part of simple dorsal rays pigmented black along their entire length (vs. pigmentation restricted to anterior two rays and proximal quarter of third simple ray); less distinct black mark at posterior tip of dorsal fin and rest of dorsal fin hyaline (vs. black mark distinct and a dense patch of chromatophores at about 2/3 of each ray); more serrae on last simple dorsal ray (25–31, vs. 16–21); smaller predorsal length (48.5–51.2 % SL, vs. 51.6–53.7; 66.8–70.9 % BL, vs. 76.4–78.8); smaller head length (27.8–29.4 % SL, vs. 32.3–33.5; 37.8–40.6 % BL, vs. 47.4–50.0; 54.7–60.2 % predorsal length, vs. 60.2–64.9); and greater interorbital width (26–33 % HL, vs. 22–25).

Figures

Fig. 3. Eirmotus octozona: a, USNM 177521, holotype, 32.1 mm SL, Thailand: Bung Borapet (?); b, ZRC 8385, 33.1 mm SL, Malaysia: Johor (?).

Fig. 7. Flank of Eirmotus species, showing dorsal fin and pre-anus patterns in: a, E. octozona, ZRC 8385, 35.6 mm SL; b, E. isthmus, ZRC 50992, 32.0 mm SL; c, E. furvus, ZRC 39152, 27.3 mm SL; and d, E. insignis, ZRC 38786, 23.2 mm SL.