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Rotenone, a commonly-used piscicide, interferes with the cellular respiration of aquatic vertebrates and invertebrates by preventing the uptake of oxygen. While dose-response relationships have been developed for fish, there are limited comparative data available on aquatic insects that respire either with tracheal gills or with a plastron – a thin layer of air trapped by hairs on the exterior of the body. This study assesses the temperature-dependent toxicity of rotenone to gill-respiring aquatic insects, family Coenagrionidae, and plastron-respiring aquatic insects, family Corixidae, at concentrations that are lethal to Mozambique tilapiaOreochromis mossambicus. Both groups of insects were found to be differentially susceptible to rotenone, with survival decreasing as functions of both increased concentration and temperature. The dose-response relationship of Mozambique tilapia was found to be similar to that of other fishes, with 100% mortality achieved at 0.025 mg l-1at both 20 °C and 28 °C. At this concentration, mortality in gill-respiring insects after 48 h was 10% at 20 °C and 28% at 28 °C, which was higher than that of plastron-respiring insects, being 2% and 7% at the same temperatures. At higher concentrations (0.05–0.10 mg l-1), however, mortality of both gill- (>50%) and plastron-respiring (>10%) insects became substantial. [ABSTRACT FROM PUBLISHER]

Most endemic freshwater fish species of the Cape Floristic Region are listed as threatened, due mainly to the impacts of invasive alien fish species. The piscicide rotenone has been identified as a potential tool to aid the conservation of indigenous species through the removal of invasive fish. Rotenone was used in the Rondegat River, Cederberg, where smallmouth bassMicropterus dolomieuhad extirpated the indigenous fish. An initial rotenone treatment in March 2012 was followed by another in March 2013. Due to concerns following the first treatment about possible build-up of rotenone between treatment stations, the second treatment included monitoring of rotenone concentrations during the treatment. Measured concentrations were consistently below the selected treatment concentration of 37.5 µg l−1and dropped to below the tested effective piscicidal concentration of 12.5 µg l−1at some sampling points. There was no build-up of rotenone within the treatment zones, but rotenone took longer than expected to clear out of the treatment area. The rotenone was effectively neutralised when the neutralisation station was operational, but was still detectable after neutralisation was terminated. [ABSTRACT FROM AUTHOR]