The exposed fish ascent to the water-air interface was also an intoxication sign. Moreover, the exposed pacu showed labial prolapsed. In both tests, the DO varied from 4.47±0.35 mg L−1 in control to 1.47±0.37 mg L−1 in TFB treatment (1000.0 mg L−1 ) in tilapia; and in the tests with pacu, from 3.3±0.44 mg L−1 in control to 1.67±0.44 mg L−1 in TFB treatment (1000.0 mg L−1). Teflubenzuron also increased the electrical conductivity of the water, which changed from 0.185±3.21 μS cm−1 in control to 0.241±0.01 μS cm−1 in TFB (1000.0 mg L−1) in the tests with tilapia; and from 0.195±0.01 μS cm–1 in control to 0.262±0.01 μS cm−1in TFB (1000.0 mg L−1)inthe tests with pacu. There was no change in the temperature or pH during the acute exposure to TFB