The Folidol 600® 96 h LC50 to O. niloticus, of 2.7 mg L−1, was lower than that of Mystus cavasius (5.9 mg L−1) [31]), Brycon cephalus [6], and the mosquito fish, Gambusia affins (8.4 mg L−1) [32]. The LC(50) 50–96 h of methyl parathion was 3.97 mg L−1 for larvae and 9.89 mg L−1 for juvenile Piaractus mesopotamicus [33]. Behavioral changes caused by methyl parathion were reported for B. cephalus [6] and Rhandia quelen [34], mostly related to erratic swimming and hyperexcitation in the latter.