Effects of paraquat on mortality and cardiorespiratory function of catfish fry Plecostomus commersoni.

The effects of a paraquat commercial herbicide formulation on an early stage of the development of Plecostomus commersoni were evaluated. Mortality, opercular ventilation rate, cardiac contraction rate and body length and weight were examined every 12 hr. The effects of the paraquat formulation on the morphology of the branchial epithelium were also examined by light microscopy. The assayed paraquat formulation significantly affected cardiac contraction and opercular ventilation. Ecotoxicologically, this could represent an important deleterious effect for early development of the catfish. Mortality data may not be sufficient for an appropriate evaluation of secondary environmental hazards associated with the application of paraquat formulation because: a) The LC-50 values for Plecostomus commersoni fry were higher than the recommended individual application rate of paraquat for aquatic weed control (0.1-2.0 mg/L). b) The estimated maximum acceptable toxicant concentration (MATC) resulted in a concentration similar to the application rate when calculated from acute toxicity tests. When the MATC was estimated from opercular ventilation or cardiac contraction rates, it was lower and fell within the recommended single application rate.