Effect of rotenone on gill-respiring and plastron-respiring insects
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 plastronrespiring aquatic insects, family Corixidae, at concentrations that are lethal to Mozambique tilapia Oreochromis 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−1 at 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.
Keywords: dose-response curves, invasive fish, Oreochromis mossambicus, piscicide