Acute toxicity of selected pesticides to the Pacific blue-eye, Pseudomugilsignifer (Pisces)

Because the larvivorous fish Pseudomugil signifer is native to southeastern Queensland and is abundant in shallow estuarine habitats, intertidal marsh es, wetland habitats, and freshwater streams, it was chosen as an indicator species for toxicologic studies with pesticides. Acute toxicity studies wi th 2 or oganophosphorus pesticides (pirimiphos-methyl and temephos) and 3 a lternate compounds under evaluation for registration in Australia (Bacillus thuringiensis var, israelensis, s-methoprene, and pyriproxyfen), were test ed in 96-h laboratory trials. Pirimiphos-methyl was the most toxic compound , with a median lethal concentration (LC50) of 0.091 ppm (0.3 times the est imated field concentration [EFC] for a 15-cm-deep pool). Temephos had an LC 50 value of 0.594 ppm (9.9 times the EFC). Bacillus thuringiensis var. isra elensis and pyriproxyfen produced LC50 values of 6.1 x 10(11) International Toxic Units (477 times the EFC) and 0.854 ppm (106 times the EFC), respect ively. s-Methoprene was the least toxic compound, with no mortality recorde d at 500 times the EFC.