Movement response of Orange-Vaal largemouth yellowfish (Labeobarbus kimberleyensis) to water quality and habitat features in the Vaal River,South Africa

Many threatened fish species that utilize riverine habitats are faced with habitat degradation and subsequent deterioration in their ecological surroundings. Habitat degradation is a consequence of water quality parameters associated with anthropogenic activities including mining, industrial, agricultural and urban activities. We examined how the movement behaviour of radio-tracked Orange-Vaal largemouth yellowfish (Labeobarbus kimberleyensis) responded to a suite of water quality chemical parameters and habitat features in the Vaal River, South Africa. We found that the probability of their movement increased with a decrease in water clarity, presence of emergent and overhanging marginal vegetation and fast flowing rapids. High mobility in conditions of low water clarity was probably related to low prey capture success of this piscivorous fish. High movement of largemouth yellowfish in emergent and overhanging marginal vegetation areas and rapid habitat biotopes were attributed to accessibility of prey within these important cover features. When water quality parameters were considered, the probability of largemouth yellowfish movement increased with increasing levels of dissolved chloride (Cl) and silicon (Si), whereas movement decreased with high phosphate (PO₄) concentrations and increased with alkalinity levels in the river. High nutrient levels associated with eutrophication caused reductions in the movement of largemouth yellowfish. The association of increased movement of largemouth yellowfish with increasing Cl and Si is indicative of degraded habitat condition in the Vaal River system. Our study showed the importance of monitoring fish behavioural movement patterns to multiple environmental parameters, as these fish are important ecological indicators when appropriate conservation and management plans of freshwater ecosystems are required.