Diagnostic description

Here are the technical details taken from the paper in which Macrognathus pavo was described.

Diagnosis

A member of the Macrognathus aculeatus species group.

Differs from all other Asian mastacembelids by the presence of only 4-6 dorsal-fin spines (vs 11-42). It differs further from all other species of the M. aculeatus group by the presence of only 6-8 rostral tooth plates (vs. 9 in M. meklongensis - 55 in M. tapirus) and details of the colour pattern.

Description
  • Body elongate, oval in cross section, but strongly laterally compressed in its caudal area
  • Depth 9.0-10.4 times in SL and body width 1.7-2.2 times in its depth
  • Head pointed with median fleshy rostral tentacle projecting from upper jaw
  • Tentacle with anterior naris at end of nasal tube originating at its subdistal tip
  • Rim of anterior naris with six fimbriae; lips fleshy
  • Jaws with numerous small, pointed teeth
  • Gill membrane connected to isthmus
  • Opercular opening large ventrally but extending dorsally only to level of horizontal through upper third of pectoral-fin base
  • Preopercular region without any spines
  • Minute scales on body, opercular area and cheek
  • A narrow band extending from above eye to posterior naris, and on base of rostral tentacle

 

  • Pectoral-fin rays 21-22. Dorsal fin with 4-6 spines and 53-55 rays. Anal fin with 3 spines and 47-51 rays. Caudal-fin rays 16-18. Dorsal, caudal, and anal fins separated, but contiguous. Pterygiophore of first dorsal fin spine inserted behind 25th- to 27th neural spine, pterygiophore of last dorsal-fin spine inserted behind 31th to 32th neural spine. First anal-fin pterygiophore inserted behind haemal spine of 31nd to 32th vertebra.
  • Anal-fin spines covered and concealed by thick skin, second spine longest. Penultimate dorsal-fin spine longest, followed by shorter last spine, completely concealed by thick skin, difficult to detect.
  • Lateral line extending from shoulder girdle in a longitudinal line, higher on body in abdominal region descending to middle of body in caudal region and ending some distance in front of caudal fin. Vertebrae: 31-32 + 41-44 = 73-76.
Colour in alcohol
  • Head and body with black stripe extending from in front of eye to horizintal through middle of anal fin base
  • Bordered dorsally by narrow, whitish to lighter brown longitudinal line from in front of eye to anterior third of caudal area
  • Upper half of side of body with light brown longitudinal band from eye to base of caudal fin
  • Middle of dorsum light brown bordered laterally by a paired dark brown to black line with irregular edge, extended posteriorly as a series of small black spots along dorsal-fin base
  • Ventral half of body lighter brown and set off distinctly against whitish ventrum
  • A series of 16 to 20 prominent small black spots along base of dorsal fin, and a series of 6 to 8 tiny black spots along posterior third of anal-fin base
  • Soft dorsal and anal fins whitish with brown oblique lines of pigment following fin rays and tiny spots in dorsal third of fin
  • Caudal fin also with brown pigment lines following fin rays and peppering of tiny black spots. Pectoral fin uniformly whitish without any marks
Colour in life

Head and body with the same markings as described above but with the posterior third of the body, and the dorsal, anal and caudal fins tinged with red.