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 g/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 g/L and 2 g/L methomyl compared to the control. However, 20 g/L and 200 g/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 g/L. Recovery data showed that the effects produced by 20g/L were reversible but not at 200g/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.