Effects of methamidophos on acetylcholinesterase activity, behavior, and feeding rate of the white shrimp (Litopenaeus vannamei).

The toxicity of methamidophos on the shrimp Litopenaeus vannamei was evaluated using acetylcholinesterase (AChE) activity, behavior, and feeding rate as effect criteria. The biochemical characterization of the soluble cholunesterase (ChE) present in both muscle and eye tissues of L. vannamei was performed in a first phase of the study. In both tissues, almost full inhibition of enzyme activity by eserine sulfate was found, indicating that the measured activity is mainly from ChE and not from other esterases. The highest rate of substrate hydrolysis was found when acetylthiocholine was used as substrate. To evaluate the effects of methamidophos on L. vannamei AChE, behavior, and feeding rate, shrimps were exposed for 24h to several sublethal concentrations of methamidophos. Significant effects of the pesticide on behavior and AChE were found, with behavior being a more sensitive endpoint than AChE inhibition. Feeding rate was not a sensible endpoint under conditions tested.