Redescription of Mystus oculatus (Valenciennes, 1840), a senior synonym of Mystus armatus (Day, 1865) (Teleostei: Bagridae)

Mystus oculatus (Valenciennes, 1840) is redescribed based on putative topotypes. It differs from congeners known from the Indian subcontinent in possessing the following combination of characters: live colouration consisting of prominent black blotch at the base of dorsal-fin spine, pale longitudinal stripes above and below lateral line, diffuse humeral blotch and a sub-triangular midpeduncular blotch; cranial fontanel almost reaching base of supraoccipital process; short adipose-fin base not reaching base of last dorsal-fin ray anteriorly; adipose-fin base 15.2–16.8 % SL; caudal peduncle depth 8.5–10.4 % SL; eye diameter 22.2–32.1 % HL and dorsal to adipose distance 17.3–23.4 % SL.

The taxonomic status of Mystus armatus, here considered a junior synonym of Mystus oculatus, is clarified. Five species groups are proposed and defined for South Asian Mystus.