Host selection and notes on the distribution of Chonopeltis australis Boxshall, 1976 in southern Africa

Abstract

The parasite Chonopeltis australis Boxshall, 1976 has been recorded from tributaries of the Orange-Vaal River System. It is host-specific, preferring the cyprinids Labeo capensis (Smith, 1841) and Labeo umbratus (Smith, 1841). Sampling was conducted between spring 2016 and autumn 2019 at various sites on the main stream of the Vaal River. The current study considers current ecological data and compares these to historic data. The species produces a single cohort, with overwintering eggs and adults. The infection of L. capensis peaks in autumn. Parasites aggregate on larger hosts that occur in riverine habitats, but can succeed in shallow impoundments with suitable hard surfaces for egg deposition. This parasite exploits changes in ecological conditions and host biology in order to survive, but will only choose between these two host species where they aggregate on larger hosts. The increased pollution in the Vaal River Barrage and downstream has had an impact on the occurrence of C. australis and it is possibly extirpated in polluted parts of the river.

Keywords: distribution, extirpation, host specificity, riverine, seasonality, Vaal River fish parasite, water quality