The catfish, Clarias gariepinus, was exposed to different acute concentrations (5-10 mg/l) of diazinon and the
Lc50 value was recorded as high as 7.3 mg/l for 96 hours. The fishes exposed to three sub-lethal levels of diazinon
(0.73, 1.095 and 1.46 mg/l) for 30 days showed that the pesticide induces changes in different blood parameters. Number
of red blood cells (RBC), haemoglobin level and haematocrit values were elevated whereas white blood cells (WBC)
count was reduced. Various blood indices like mean corpuscular volume (MCV), mean corpuscular haemoglobine
(MCH) and mean corpuscular haemoglobine concentration (MCHC) vary insignificantly in the fish treated with diazinon.
Glucose level and activity level of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) was increased
in Clarias gariepinus exposed to diazinon. Protein level in plasma of fish treated with pesticide was changed but the
change was insignificant. Histological changes in the liver, gills and kidney of fishes exposed to diazinon were apparent
when compared to control. Hepatocytes necrosis and bleeding were more distinct in the fishes exposed to pesticide.
Glomerulus hypertrophy and bleeding in kidneys; and fusion and degeneration of secondary lamellae and epithelial
hyperplasia in gills were also observed in the exposed fish.
Keywords: acute toxicity, histological changes, blood profile, diazinon, Clarias gariepinus.