Lethal concentration of Cu in the neotropical fish Cnesterodon decemmaculatus (Pisces, Cyprinodontiformes)

Copper is a classic limiting factor of fishes, as it is both essential and toxic. In small amounts the element is a vital micronutrient needed for haemoglobin synthesis and a major component of cytochrome oxidase. Indeed, most fishes will selectively accumulate copper from surrounding water independent of actual concentrations. As concentrations exceed metabolic requirements, however, copper becomes injurious to fishes, and ultimately reaches lethal levels if concentrations continue to increase. Most research on fish toxicity was carried out on the holartic fauna, while metal toxicity on neotropical fish remains mainly unreported. Cnesterodon decemmaculatus, a widely distributed endemic small fish of neotropical America, which fulfils requested conditions for toxicity tests, has been used in water quality assays (De la Torre et al. 1997; Garcia et al. 1998), in Zn toxicity tests (Gomez et al. 1998), and to evaluate its resistance to changes in water pH (Gomez and Toresani 1998). The present contribution assesses Cu lethal concentration (LC50) on C. decemmaculatus by means of static acute bioassays in natural water. Obtained results will be used to stablish sublethal concentrations for chronic bioassays.