Vanmanenia orcicampus

Maurice Kottelat, 2017, Vanmanenia orcicampus ı a new species of loach from the Plain of Jarsı Laos (Teleostei: Gastromyzontidae), Ichthyol. Explor. Freshwaters 28 (1), pp. 87-95 : 88-91

Vanmanenia orcicampus ı new species ( Figs. 1-2 )

Holotype. MHNG 2767.094 ı 47.5 mm SL; Laos: Xiangkhouang Province: Nam Ngum at Ban Khangviangı 19°34'47"N 103°17'42"Eı 1138 m asl; M. Kottelatı T. Phommavong & B. L. Amathı 2 March 2012.

Paratypes. CMK 22732 ı 5 ı 20.6-23.2 mm SL; collected with the holotype.

Diagnosis. Vanmanenia orcicampus is distinguished from the other species of the genus by its unique colour patternı made of a midlateral row of six blotchesı anterior two longitudinally elongatedı 3rd to 5th roundishı 6th faintı at posterior extremity of caudal peduncle; a middorsal row of three predorsal and three postdorsal saddlesı 3rd predorsal one extending backwards along dorsalfin base; and vermiculations between saddles and blotches and on lower half of flank. It is further distinguished from congeners in having a slender caudal peduncle whose depth is 1.5 times in its length and 2.5 times in body depth; and 12-14 branched pectoral-fin rays.

a b Description. Based on holotype only. See Figures 1-2 for general appearance and Table 1 for morphometric data of holotype. A moderately elongate Gastromyzontidae with arched dorsal profileı body depth regularly increasing up to slightly in front of dorsal-fin originı decreasing under dorsal-fin base. Behind dorsal finı body depth decreasing regularly to slightly in front of caudal-fin base. Dorsal profile continuous between head and body. Ventral profile slightly convex. Preventral part of belly and lower surface of head flat. Head slightly depressed; body slightly compressed. Interorbital area flat. In lateral viewı eye flushed with dorsal profile of head. Snout rounded. Depth of caudal peduncle 1.5 times in its lengthı tapering posteriorlyı and 2.5 times in body depth. Largest recorded size 47.5 mm SL.

Dorsal fin with 4 unbranched and 7 (2) or 7 1 / 2 (4*) branched rays; distal margin almost straight; 1 st and 2nd branched rays longest. Pectoral fin with 1 unbranched and 12 (2) or 13 (4*) branched rays (including small last rayı unbranched)ı roundedı reaching 3 / 4 of distance to pelvic-fin base. No axillary pectoral lobe. Pelvic fin with 1 unbranched and 8 (4) or 9 (2*) branched rays (including small last rayı unbranched); reaching about ¾ of distance to anus; rounded; origin below base of branched dorsal-fin rays 2-3; axillary lobe presentı freeı extending on 1 st and 2nd branched rays. Anus situated at about 1 / 3 of distance between pelvic-fin base and anal-fin origin. Anal fin with 3 unbranched and 5 1 / 2 (6*) branched rays; distal margin convex. Caudal fin with 7+ 7 (6*) branched rays; about 6 dorsal and about 4 ventral procurrent rays; forkedı lobes roundedı of equal length. Upper 4 and lower 4 principal caudal-fin rays adnate (without membranes) until about first branching point.

Body entirely covered by scalesı except on belly in front of anus. Most scales with an acuminate projection on posterior marginı tip often fleshyı sometimes appearing as ‘soft tubercles’. Lateral line completeı not extending on caudal-fin baseı with 79 pored scales.

Anterior nostril pierced in front side of a pointed flap-like tube. Posterior nostril adjacent to anterior one. Mouth archedı gape about 2 times wider than long ( Fig. 3 b). Two pairs of rostral barbels and one barbel at each corner of mouth. Rostral groove shallow between rostral barbelsı deeper from base of outer rostral barbel backwards; edge of rostral fold with three fleshy lobes between rostral barbels. Lips very finely papillatedı continuous around corner of mouth. Upper lip fleshyı appearing as three transverse layers: two fleshly layers and a narrow intermediate oneı smoothı harderı slightly protrudingı not reaching corner of mouth. Lower lip in three partsı each about of equal lengthı separated by small notches; median part thinı papillated along anterior edge; lateral parts thick and fleshyı with a small projection at midlength; postlabial groove restricted to behind lateral parts. Mouth structure of juvenile ( Fig. 3 a- b) as adultı except that mouth is narrowerı lower jaw exposed. Notches between three parts of lower lip not very marked; lateral parts close togetherı more or less in contact mesiallyı where fleshier and with two short projections and in some individuals forming a ridge with contralateralı wide and thin towards maxillary barbel with a short projection along median edge. Gill opening extending downwards in front and below base of anterior pectoral-fin ray.

Tubercles on all surfaces of headı finer on snout and top of headı larger but smooth on ventral surfaceı large and densely set on opercle. Unculiferous pads (sensu Conway et al. ı 2012): in pectoral finı well developed along anterior edge of unbranched ray and behind unbranched and first seven branched raysı hardly distinct on remaining branched rays; in pelvic finı well developed along anterior edge of unbranched ray and behind unbranched and first three branched rays.

Coloration. After about one month in formalin. Adult: Head and body background colour pale yellowish brownı throatı bellyı lower part of caudal peduncle whitish; except otherwise statedı markings dark brown. Head with a dark blotch in interorbital area and on posterior part of head; snoutı suborbital area and opercle variegated.

Body with three predorsal and three postdorsal saddles; third predorsal saddle extending backwards along (but not touching) dorsal-fin base; saddles restricted to middorsal areaı not extending down side. A midlateral row of six blotchesı anterior two longitudinally elongated; 3rd to 5th roundish; 6th faintı at posterior extremity of caudal peduncle. Vermiculations between rows of saddles and blotches and on lower half of flankı paler brown than saddles and blotches. A blackish band between posterior extremity of second blotchı connecting it with its contralateral across base of dorsal fin.

Dorsal fin hyalineı with two irregular rows of spotsı most located on rays and membranes between branches at level of 1 st and 2nd branching points (and at similar position on last unbranched ray). Caudal fin hyalineı with three vertical rows of spotsı first one near base of raysı second and third one on rays and membranes between branches near branching points; spots on first row appearing as a blotch on lower and upper most rays (not separated by membranes at this position). Anal fin hyalineı with an elongated mark on raysı mainly near branching points. Pelvic fin hyalineı with two irregular rows of spotsı one in proximal position on posterior raysı one on rays and membranes between branches near branching points. Pectoral fin hyalineı with three irregular rows of spotsı one in proximal position on posterior raysı one on rays and membranes between branches near branching points of all rays (faint on posterior rays)ı and one in similar position but absent on posterior rays.

Juveniles: Body background colour yellowish whiteı marking dark brown. Four juveniles ( Fig. 2 a) with three large blotches along lateral lineı connected by a broad band over lateral line. First blotch connected with contralateral across back by a band of paler brown pigmentsı in position of second saddle in adult. Second and third blotches connected with contralaterals across back by band of similar pigmentsı in positionı respectivelyı of blackish band across dorsal-fin base and of 5th saddle in adult. Blotches and transverse bands resulting in four elliptic pale areas (anterior one not sharply contrasted)ı with a patch of pale brown pigments in centre of eachı in position of 1stı 3rdı 4th and 6th saddles in adult. A conspicuous black blotch on proximal 1 / 3 of dorsal fin.

In largest juvenile ( Fig. 2 b; only 3 mm longer than smallest)ı pattern still distinctı but blotches smallerı restricted to along lateral line and forming a very irregular stripe. Blotch on caudal fin fainter.

Distribution and habitat. Vanmanenia orcicampus has been collected only once in the upper Nam Ngum at the northern edge of the Plain of Jars. The Nam Ngum crosses the western part of the plain before descending westwards through 110-km long gorges until the Nam Ngum 2 reservoir and then to the Mekong. It was not present in the other 44 sites sampled in the Nam Ngum watershed downstream of the plain. The plain is also drained to the south by the Nam Ngiep (another Mekong tributary) and the Nam Neunı which flows to Vietnam (as Song Lam) and reaches the Gulf of Tonkin. It is possibly present in the Nam Ngiep and Nam Neun on the plain but sites with an appropriate topography could not be sampled. It was not present at 33 sites in the Nam Ngiep watershed (a Mekong tributary) and 11 sites in the Nam Neun drainage (which flows directly to the Gulf of Tonkin) downstream of the plain.

At the type localityı the Nam Ngum was a sluggish stream in an open agricultural area ( Fig. 4 ). The bottom was made of sand to cobbleı at places covered by mud. The current was slow. This is unlikely to be the original habitatı which was probably pebble to stone bottom. The juveniles were caught among gravel and pebble. The adult was obtained among bamboos used to build a weir. The other species present were a mix of species usually found in streams with fast current and clear water ( Devario cf. laoensis ı Poropuntius angustus ı Scaphiodonichthys acanthopterus ı Schistura defectiva ı S. quaesita ı Rhinogobius milleri ) and species typical of sluggish waters and swamps ( Puntius brevis ı Systomus jacobusboehlkei ı Channa gachua ı Macropodus opercularis ).

Etymology. From the Latin nouns orca (jar; dative plural: orcis) and campus (plainı field)ı literally the plain with the jarsı reference to the type locality on the Plain of Jars. A compound noun in apposition.

Figures

Fig. 1. Vanmanenia orcicampus ı MHNG 2767.094 ı holotypeı 47.5 mm SL; Laos: Nam Ngum on Plain of Jars.

Fig. 2. Vanmanenia orcicampus ı CMK 22732 ı paratypes; Laos: Nam Ngum on Plain of Jars; aı 20.6 mm SL (reversed); and bı 23.2 mm SL.

Fig. 3. Vanmanenia orcicampus ı mouth. aı CMK 22732 ı 20.6 mm SL; bı CMK 22732 ı 22.1 mm SL; and cı MHNG 2767.094 ı holotypeı 47.5 mm SL.

Fig. 4. Nam Ngum at Ban Khangviangı Xiangkhouang Provinceı Laos; type locality of Vanmanenia orcicampus. Juveniles were found among the pebbles and cobble in the foreground rightı adult among the bamboos of the weir.

Tables

Table 1. Morphometric data of holotype of Vanmanenia orcicampus.

Standard length (mm)	47.5
Total length (mm)	61.3
In percent of standard length
Total length	129.2
Head length (dorsal)	23.5
Head length (lateral)	23.3
Predorsal length	49.0
Prepelvic length	50.9
Pre-anus length	61.8
Pre-anal length	79.1
Head depth	13.3
Body depth at dorsal-fin origin	20.6
Depth of caudal peduncle	8.3
Length of caudal peduncle	12.8
Head width	17.8
Body width at dorsal-fin origin	16.8
Snout length	11.5
Eye diameter	5.0
Interorbital width	7.8
Mouth width	4.5
Length of dorsal fin	23.0
Length of upper caudal-fin lobe	28.7
Length of median caudal-fin rays	23.5
Length of lower caudal-fin lobe	27.4
Length of anal fin	18.8
Length of pelvic fin	23.5
Length of pectoral fin	27.2
Distance between pelvic-fin bases	5.2
In percent of lateral head length
Snout length	49
Eye diameter	21
Interorbital width	34
Mouth width	49