Acute toxicity of the pesticides, maneb and carbaryl, to juvenile rainbow trout were evaluated under static-renewal test conditions. Actual concentrations of maneb ranged from 0.10 mg/L to 2.00 mg/L and carbaryl ranged from 0.20 mg/L to 3.90 mg/L The concentrations of maneb that killed 50% of the rainbow trout (3.27 +/- 0.9 g) within 24-h (24-h; LC50), 48-h, 72-h and 96-h were 1.19 +/- 0.12, 1.04 +/- 0.11, 0.92 +/- 0.12 and 0.81 +/- 0.14 mg/L (95% confidence limits), respectively. LC50 values of carbaryl for 24-h, 48-h, 72-h and 96-h were 2.52 +/- 0.71, 2.16 +/- 0.63, 1.71 +/- 0.46 and 1.39 +/- 0.15 mg/L, respectively. None of the unexposed control fish died and the first fish died 6h after exposure to maneb (>= 1.30 mg/L), and carbaryl (>= 2.60 mg/L). Lamellar edema, separation of epithelium from lamellae, lamellar fusion, swelling of the epithelial cells and epithelial cell necrosis were observed on maneb and carbaryl exposed fish. Gills also had scattered areas of focal lamellar hyperplasia. Fish exposed to pesticides had inflammation and focal necrosis in liver, trunk kidney and spleen. Maneb and carbaryl had similar histopathological lesions. In order, the most affected organs were gill, trunk kidney and liver. (C) 2010 Elsevier Ltd. All rights reserved.