Taxonomy

Based on the number of vertebrae and its plain colour Pangio longimanus can be assigned to the oblonga-group, as defined by Kottelat and Lim (1993).

Detailed description

1 male (holotype) and 2 females (paratypes) studied.

Pectoral fin of male Pangio longimanus

Ventral view of male Pangio longimanus pectoral fin, showing the hypertrophied and extremely elongated 2nd fin ray. (Image: Ralf Britz, Natural History Museum)

General characteristics:
  • Elongate body, only slightly compressed laterally
  • Mid-body cross section almost circular to slightly oval
  • Body depth 1.4-1.6 times its body width
  • Standard length 9.6-12.6 times its body depth
  • Caudal peduncle moderately laterally compressed, its depth 1.3-2 times its width, its length 1.8-2.5 times its depth, with distinct, but low, dorsal and ventral adipose keels.
  • Mouth: 6 barbels (2 pairs of maxillary and 1 pair of mandibular barbells). Median lobe of lower lip extended into short barbel.
  • Posterior margin of anterior naris developed into a long pointed flap, often referred to as nasal barbel.
  • Bifid spine below eye
  • Eye covered by thick skin
  • Opercular opening restricted to small orifice above pectoral-fin base
  • Caudal fin truncate to slightly emarginated
Lateral and dorsal views of male Pangio longimanus specimen

A male Pangio longimanus eel-loach from Laos. This holotype specimen (ZRC 51933) measures 20.2mm standard length. Top = lateral view, bottom = dorsal view. (Images: Ralf Britz, Natural History Museum)

Vertebrae and ray characteristics:
  • Total vertebrae: 46 or 47
  • Pectoral-fin rays: 7
  • 2nd pectoral ray of male hypertrophied with segments of hemitrichs up to 6 times as wide as those of adjacent rays and extremely elongated, longer than head, with posterior tip folded back, reaching 9th myoseptum (to 6th in female).
  • Posterior end of pelvic girdle at level of 22nd vertebra
  • Anterior base of anal fin only slightly behind vertical through posterior base of dorsal fin
  • Pelvic-fin rays: 6
  • Dorsal-fin rays: 9 or 10, with 2 or 3 unbranched followed by 6 branched rays and last unbranched ray
  • Anal-fin rays: 9, with 3 unbranched followed by 5 branched rays and last unbranched ray
  • Caudal-fin rays: 8+8 or 8+7
  • Dorsal procurrent rays: 3 to 6
  • Ventral procurrent rays: 4 to 6
Lateral and dorsal views of female Pangio longimanus specimen

A female Pangio longimanus eel-loach from Laos. This paratype specimen (CMK 19692) measures 22.9mm standard length. Top = lateral view, bottom = dorsal view. (Images: Ralf Britz, Natural History Museum)

Colour of specimens in alcohol:
  • Background colour yellowish-light brown, with numerous brown chromatophores giving fish a freckled appearance.
  • Chromatophores dense on top and side of head.
  • In area of body between head and a vertical through base of pelvic fin, brown chromatophores extend from dorsal midline, where more densely set, to dorsal half of body. 
  • In abdominal area, chromatophores extend further ventrally, covering upper three quarters of side of body.
  • At level of anus chromatophores reach down to base of anal fin. Further posteriorly chromatophores cover entire caudal peduncle including adipose keels.
  • Brown chromatophores also present along modified pectoral ray of male, at base of pelvic fin in 1 female and male, and lining dorsal, anal and caudal-fin rays in both sexes.
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