This study investigated the physiological effects of a pesticide based on Bacillus thuringiensis (Dipel-WP ®) added in the water and diet of Piaractus mesopotamicus during 24 and 48 h. It was added 0.13 g of de B. thuringiensis per kg of commercial feed; and for the fish subjected to the biopesticide in the water of the tanks, it was added 0.13 g/l of the biopesticide. Plasma levels of sodium, chloride, potassium, cholesterol, glucose, triglycerides, cortisol, total protein, alanine aminotransferase (AlT), aspartate aminotransferase (AST), hematocrit, hemoglobin, erythrocytes number, mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC), number of thrombocytes and leukocytes were determined. Cortisol, lactate, glucose, total protein, cholesterol, triglycerides, AlT, AST, sodium, potassium, hematocrit, hemoglobin, MCV, number of erythrocytes, leukocytes, lymphocytes, eosinophils and PAS-positive granular leukocytes suffered alterations derived from the addition of B. thuringiensis in water and diet of the fish. The toxicity of the concentrations of biopesticide in short-term exposure in water and diet of the fish led to blood alterations (increase or decrease). Therefore, care must be taken to avoid a possible prolonged contamination in the tanks of fish farming by agricultural pollution based on B. thuringiensis.

The use of biopesticides based on Bacillus thuringiensis (Berliner 1915) in agriculture has been considered harmless for non-target organisms such as fi sh. The present study aimed to investigate the effects of a biopesticide based on B. thuringiensis on the physiology and histology of the liver, kidney and intestine of Arapaima gigas (Schinz, 1822), via exposure to water (0.13 g/L) and in the diet (0.13 g), after 24 and 48 h. Fish subjected to B. thuringiensis in the water of their breeding and feeding tanks exhibited mortality due to changes in erythrogram (hematocrit, hemoglobin, erythrocytes), thrombogram and leucogram blood parameters, and plasma (sodium, chloride, potassium, cholesterol, glucose, triglycerides, cortisol and total proteins) and enzymatic (Aspartate Amino Transferase and Alanine Amino Transferase) biochemistry.Histopathological alterations in the liver and kidney ranged from mild to severe and were characterized by the presence of cytoplasmic vacuolization, nuclear hypertrophy and atrophy, melanomacrophage centers and necrosis, and in the intestine by changes to the number of villi and goblet cells. Therefore, these physiological and histopathological alterations indicate that care should be taken with the dispersion of biopesticides based on agricultural B. thuringiensis in fi sh farming.