Effect of methomyl on sex steroid hormone and vitellogenin levels in serum of male tilapia ( Oreochromis niloticus ) and recovery pattern

Tilapia were exposed to sub‐lethal concentrations of 0, 0.2, 2, 20 or 200 μg/L for 30 days, then transferred to methomyl‐free water for 18 days. E 2 , T, 11‐KTand VTG in serum were examined. There were no significant changes in all the parameters in serum of tilapia exposed to 0.2 μg/L and 2 μg/L methomyl compared to the control. However, 20 μg/L and 200 μg/L have the potential to disrupt the endocrine system of male tilapia, as shown by its ability to increase VTG and E 2 and decrease T and 11‐KT in serum. Thus it would appear the no observed adverse effect level for sexual steroid hormones of methomyl is lower than 2 μg/L. Recovery data showed that the effects produced by 20μg/L were reversible but not at 200μg/L. Furthermore, the sensitivity of above parameters to methomyl followed the order of VTG>E 2 >11‐KT>T>GSI, suggesting VTG being the better biomarkers.