Original description as Chromis johnstoni:
- Günther, Albert C. L. G. 1893. "Second report on the reptiles, batrachians, and fishes transmitted by Mr. H. H. Johnston, C. B., from British Central Africa". Proceedings of the Zoological Society of London. (4); pp. 616-628 (crc00060)
- Haplochromis sexfasciatus Regan, 1922, with type locality at Lake Malawi. Determiner: Trewavas, 1935
Conservation: Placidochromis johnstoni is evaluated by the international union for the conservation of nature in the iucn red list of threatened species as (LC) least concern (2018).