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Micropanchax johnstoni (Günther, 1894)
by Michael K. Oliver, Ph.D.Johnston's topminnow, Micropanchax johnstoni, is a small (60 mm or 2.3 inches), killifish-like denizen of near-surface waters in Lake Malawi's lakeshore swamps. (A photograph of live individuals by Diane Brown is available at Killi.net here.) It was long known as Aplocheilichthys johnstoni but Micropanchax is now its correct genus. Males attain a larger size than females. Jubb (1967) describes the coloration as "iridescent olive-green with lemon coloured fins and belly. In some specimens the dorsal and caudal fins are edged with black." It occurs throughout "...the warm waters of the whole Zambezi River system, and southwards to the lowveld areas of the Pungwe, Buzi, Sabi, Lundi, and Limpopo rivers" (Jubb, 1967). M. johnstoni is one of two species of Micropanchax now known from the environs of Lake Malawi; the other one, M. katangae, has a distinct black stripe extending from the snout to the caudal fin base.
Jackson (1961: 557) remarked that M. johnstoni had not been seen in Lake Malawi since collections made by Sir Harry H. Johnston (after whom M. johnstoni was named) and Dr. Cuthbert Christy; i.e., since 1925, when the latter made his great collection. In 1968, however, on my first visit to Lake Malawi, I collected a series of M. johnstoni at Monkey Bay in the lake proper, in sheltered waters over a Vallisneria bed beside the Fishery Research Unit jetty. I recorded the local name "Nkongola" being used for this fish at Monkey Bay. Later, in August 1980, colleagues and I collected a total of 22 individuals of M. johnstoni measuring from 10 to 36 mm SL from the submerged parts of two "floating islands" of swamp vegetation (one composed of papyrus, the other of reeds) that had become detached from lakeshore swamps by wind and wave action and were drifting around the southwest arm, south of Thumbi Island West (Oliver & McKaye, 1982).
Johnston's topminnow is a serial spawner which deposits its eggs in aquatic plants. The adults swim and live in the shallows, primarily in the uppermost 10 cm (4 inches) of the water, and feed on daphnia, insect larvae, and other small invertebrates (Steenkamp et al., 2001).
Long considered true killifishes (Cyprinodontidae), this and the other members of the genus Micropanchax are now classified as egglaying members of the generally livebearing family Poeciliidae, based on considerable anatomical evidence from the skeleton (Parenti, 1981).
The above color painting by Dave Voorvelt is copyright © by the South African Institute for Aquatic Biodiversity (formerly known as the J.L.B. Smith Institute of Ichthyology). It is reproduced here from Skelton (1993) with the kind permission of Prof. P.H. Skelton.
The illustration of M. johnstoni below,
drawn by Hilda M. Jubb, is from Jubb (1967) and is used here by gracious
permission of Mr. A. T. Balkema of A. A. Balkema Publishers, Rotterdam.
