Effect of organophosphorus pesticide Chlorpyrifos on thyroid hormone changes in grass carp (Ctenopharyngodon idellus)

Chlorpyrifos is one of the strong organophosphate pesticides that use very much and lead poisoning, disruptor in immune and physiology systems and live activities of aquatic organisms. Therefore, its effects can use as the biological indicator in a determination of pollutants. In this study, the effect of different concentrations of Chlorpyrifos (5, 10, 20, 30 and 40 mg/L) were investigated on thyroid hormones of grass carp (Ctenopharyngodon idellus) during 14 days. Blood sampling performed in 12, 24 and 96h and also 7 and 14 days after the exposure. The concentrations of serum thyroid hormone were determined using Radioimmunoassay method. Results showed the significant decrement in the serum T3 and increment of the serum T4 in the treated fishes in comparison to the control groups. In addition, the decrement in ratio T3/T4 was observed (P