Four new species of Rainbowfishes are described from the Arguni region. These species are allied to the species already known from the Bomberai Peninsula and the Bird’s Neck, namely Melanotaenia ammeri, M. irianjaya, M. kokasensis, M. parva and M. angfa. The new species M. urisa is characterised by a thin and elongated body, a long predorsal length, a short preanal length, a long and thin caudal peduncle, short fins and by relatively large eyes. In contrast, M. arguni sp. nov. is distinguished from all of its congeners by small eyes, a thin body, a moderately long predorsal length, a long preanal length, and a short and thin caudal peduncle. Melanotaenia veoliae sp. nov. displays an original pattern of colouration, few cheek scales, a large interorbital width and a long spine length on the anal fin. Melanotaenia wanoma sp. nov. is recognised by an elongated body with a short and thin caudal peduncle, a short predorsal length with a long total dorsal fin, a long preanal length and a prominent margin stripe present on anal and second dorsal fin.