Can be diagnosed from its congeners by possessing the following characters: 44 dentary teeth, counted on single ramous only; 43 maxillary teeth; orbit diameter 1.5, relatively small compared to similar-sized individuals; interorbital width 4.1, relatively narrow; parietals with pronounced posterior projections that are pointed and curve slightly toward the midline; caudal fin widely separated from dorsal and anal fins by relatively long caudal peduncle, 9.7; caudal-peduncle length divided by peduncle depth 2.4; 26 anal-fin rays, with distinctly shorter basal length than that of dorsal fin; dorsal and anal fins extremely low in profile (dorsal-fin base divided by longest dorsal-fin ray about 7; longest dorsal-fin ray in anterior third of fin); and first pectoral-fin ray not (or only slightly) enlarged in diameter and with proximal tip similar in form to second and subsequent pectoral-fin rays. Can be further distinguished from Arapaima gigas by having single row of small teeth on dentary (vs. 2-2.5 rows of enlarged teeth in A. gigas ) (Ref. 93668).