In acute toxicity tests based on the loss of positive rheotaxis, the relationship between exposure time and bis (tri-n-butyltin) oxide concentration was determined for Sulmo gairdneri and TiZapia rendalli. This relationship may be represented by two superimposed rectangular hyperbolas (X-a) ( Y-b) =c corresponding to two poisoning mechanisms.The 24-h ECSo is 30-8 pg/1 for trout and 53.2 Fg/l for T. rendalli. A histopathological study on S. gairdneri shows concentrations from 5.85 to 0.0117 mg TBTO/l resulted in damage to the gill epithelium. At low concentrations a degeneration of the cornea and damage to the epithelial cells of bile ducts were also observed. Prior to a loss of positive rheotaxis and with concentrations from 0.023 to 1.17 mg/l, the packed cell volume, the haemoglobin concentration and erythrocyte count increased. Determination of the mean cell volume showed swelling took place at 1.17 mg/l but shrinkage was observed at 0.053 mg/l. These results indicate that TBTO interfered with the process of respiration.A ' safe level ' (0.1 pg/l) is proposed for schistosomiasis control.

No abstract