Danio annulosus can be diagnosed from other congeners, except D. assamila, D. dangila, D. catenatus, D. concatenatus, and D. sysphigmatus, by produced first ray in pectoral and pelvic fins, large cleithral spot, and pattern of dark rings enclosing light interspaces on the side. It differs from these species by slightly horizontally extended cleithral spot (vs. vertically extended in D. dangila, round in the other species), anterior interstripe Ia usually present (vs. absent in D. dangila and D. catenatus), rings in series along side elongate, width of each dark ring of about same as diameter of light centre or wider (vs. elongate, with narrower dark ring in D. sysphigmatus, round or slightly elongate and with dark ring about as wide as light centre in other species), ring pattern usually not extending onto caudal peduncle (vs. present on part of caudal peduncle in D. dangila, D. catenatus and D. concatenatus), 34- 35 lateral-line scales (vs. 35-38 in D. sysphigmatus), pectoral fin barely or not reaching to base of pelvic fin, unbranched leading ray only slightly longer than remaining rays (vs. leading ray prominently elongated, reaching to base of unbranched pelvic-fin ray or beyond), pelvic fin without produced unbranched ray, not reaching to vent (vs. with unbranched ray distinctly longer than the rest, and reaching to vent or bases of anterior anal-fin rays) (Ref. 104133).