Eirmotus isthmus Tan & Kottelat 2008

Differs from other congeners by having subinferior mouth, with a narrow lower jaw whose tip is angulous in ventral view. Can be further differentiated by the presence of small black mark immediately in front of anus with scattered chromatophores near it, visible in lateral view; lacking or very faintly marked bar 1; simple dorsal-fin rays black, black mark not reaching the first branched ray, rest of fin hyaline; posterior margin of last simple dorsal-fin ray with 22-26 serrae; bars narrow, width of bar 5 equal to ½ or less lateral row scale (Ref. 78741).

Dorsal soft rays (total): 11; Analsoft rays: 8; Vertebrae: 29 - 31

Occurs in lakes and large permanent water bodies in the floodplain. Caught in water column together with Hyalobagrus flavus (Bagridae), Pseudeutropius brachypopterus, P. moolenburghae (Schilbeidae) and Gymnochanda filamentosa (Ambassidae) (Ref. 78741).