Ambassis octava sp. nov. (Teleostei: Ambassidae) is described on the basis of eight specimens collected from the west and east coasts of Peninsular Malaysia. The new species closely resembles Ambassis nalua (Hamilton 1822), both species having body about twice as long as deep, continuous lateral line, no nasal spine and two transverse scale rows on cheek. However, the new species is distinguishable from A. nalua by having second anal-fin ray shorter than third one (vs. equal or longer), 15–17 gill rakers on lower limb of first branchial arch (vs. 19–21), more predorsal scale count (13 or 14) (vs. 11 or 12, modally 12), and interopercle lower margin and preorbital ridge smooth (vs. serrate). In addition, A. nalua and the new species are separated by 14.5% mean uncorrected p-distance in the mitochondrial cytochrome oxidase subunit I (COI) gene. The description of A. octava is only the second description of a new species of Ambassis in Southeast Asia in the last 100 years.

Ambassis octava sp。十一月 （Teleostei：Ambassidae）根据从马来西亚半岛西海岸和东海岸收集的八个标本进行描述。这个新物种与Ambassis nalua (Hamilton 1822) 非常相似，这两个物种的身体长度大约是深的两倍，连续的侧线，没有鼻棘，脸颊上有两排横向鳞片。然而，新物种与A. nalua的区别在于第二个臀鳍鳍条短于第三个（相对于等于或更长），第一鳃弓下肢有 15-17 个鳃耙（相对于 19-21），更多的前鳞片计数（13 或 14）（对比 11 或 12，模态 12），鳃间下缘和眶前脊光滑（对比锯齿状）。此外，A. nalua新物种在线粒体细胞色素氧化酶亚基 I (COI) 基因中的平均未校正p距离为 14.5%。A. octava的描述只是近 100 年来东南亚对Ambassis新种的第二次描述。