TOXICIDAD AGUDA DEL HERBICIDA PARAQUAT EN Oreochromis niloticus (CICHLIDAE) Y Macrobrachium olfersii (PALAEMONIDAE).

Paraquat is an herbicide used in the agricultural industry for weed and undergrowth control, its mode of action is by contact and non-selective. Due to its high-water solubility and low volatility, it represents a potential risk for non-target organisms. Oreochromis niloticustilapia and the prawn Macrobrachium olfersiiare important commercial species for Veracruz´s aquaculture industry. The objective of this study was to determine the Mean Lethal Concentration (LC50) of the herbicide Dasurquat® (active ingredient Paraquat) through an acute toxicity bioassay (96 hours). Juvenile O. niloticus(average weight = 10 mg, total length = 8.75 mm) and juvenileM. olfersiipostlarvae (average weight = 5 mg, total length = 5.72mm) were used as test specimens. Five herbicide concentrations (5, 10, 20, 40 and 80 µl/L for tilapia and 0.1, 0.2, 0.5, 0.7 y 1 µl/L for prawn) were applied. The experimental design considered a negative control, with two replications and two replicates for each treatment. Probit analysis determined that the LC50at 96 hours for O. niloticuswas 17.49 µl L-1, with a lower 95 % confidence limit of 13.75 µl L-1and an upper limit of 22.25 µl L-1, whereas for M. olfersiithe LC50at 96 hours was 0.31 µl L-1, with a lower 95 % confidence limit of 0.26 µl L-1and an upper limit of 0.35 µl L-1. The analysis of variance showed that there was no significant statistical difference (p >0.05) between the replicates of the treatments. It is concluded that it is necessary to continue evaluating its toxicity in aquatic organisms due to the wide use of this herbicide in Veracruz´s agricultural activity, to determine its potential risk to other activities.