Cnesterodon decemmaculatus juveniles as test organisms in toxicity assessment: cadmium case.

The poeciliid Cnesterodon decemmaculatus is one of the native species of southern South America recently recommended for use as a test species in biomonitoring. Therefore, it is important to characterize its responses to stress conditions caused by pollution. The aim of this work was to determine the toxicity of the reference toxicant cadmium (Cd) and to evaluate the lethality response of juveniles of C. decemmaculatus exposed to an environmental sample with a high degree of pollution (Luján River, Buenos Aires, Argentina). The LC₅₀ values at 24 and 96 h were 6.00 and 2.27 mg Cd/L, respectively. The uptake of Cd was significantly greater in the first 24 h in relation to the total time of exposure in the bioassay. The toxicity of the water was in agreement with the level of contamination. A Cd contaminant pulse exerted an important additive effect on the toxicity of the environmental sample. The results provide information regarding the sensitivity of a native species to be used as a test organism in environmental monitoring.