Sensitivities of mosquitofish and black mudfish to a piscicide: Could rotenone be used to control mosquitofish in New Zealand wetlands?

Abstract

The comparative sensitivities of mosquitofish (Gambusia affinis) and black mudfish (Neochanna diversus) to the piscicide rotenone were investigated to determine whether it is feasible to use rotenone to control mosquitofish in wetlands inhabited by mudfish. Mosquitofish were exposed to four nominal rotenone concentrations (56, 79, 112, 158 μg.L‐1) and the time taken for 50% (ET50) and 90% (ET90) of individuals to gasp at the water surface was recorded. Fish were removed from the rotenone at this stage and placed in rotenone‐free water to recover. Mudfish were exposed to a single nominal rotenone concentration (100 μg.L‐1), and removed when hanging at the surface and gulping air. The response time of mosquitofish decreased with concentration. Mean ET50 values were 158 and 26 min for 56 and 158 μg.L‐1 rotenone, respectively. Mean ET90 values were 246 and 36 min, respectively. Mudfish were approximately twice as sensitive as mosquitofish to 100 μg.L‐1 rotenone. All mudfish recovered following exposure to rotenone. The management implications of the findings are discussed. We suggest that if rotenone were to be used to control mosquitofish in wetlands, it could be applied in summer to remnant standing water as repeated doses of 100-200 μg.L‐1. © 2000 Taylor and Francis Group, LLC.