Macrognathus aureus is a member of the M. aculeatus species group. It differs from all other members of this species group by the following combination of characters: rostral tooth plates 8–10, dorsal-fin spines 21–22, and a unique colour pattern consisting of a series of large white rimmed dark-brown to black blotches along the dorsal fin and even larger black blotches along the lateral line, of which some are confluent with the dorsal series. In particular it differs from M. aral, M. lineatomaculatus, M. pentophthalmos, M. siamensis, M. tapirus, and M. aculeatus in having fewer rostral toothplates (8–10 vs 11–55), from M. pavo, M. morehensis, M siamensis, M. meklongensis, and M. pentophthalmos in having a greater number of dorsal-fin spines (21–22 vs 4–18). The only species of the M. aculeatus group with a similar range in the number of rostral tooth-plates and dorsal-fin spines is M. obscurus, from which the new species differs in its colour pattern (large white rimmed dark brown to black blotches along the dorsal fin and the lateral line, of which some are confluent with the dorsal series, vs minute or absent dorsal fin spots and absence of lateral line blotches) (Ref. 84451).