Factors affecting cholinesterase activity in aquatic animals

Abstract

Organophosphorus (OP) insecticides are extensively used to control crop pests, and can enter aquatic systems draining agricultural watersheds. Because OPs are highly toxic to aquatic organisms, monitoring is important, yet difficult due to the low persistence of OPs. Inhibition of activity in cholinesterase (ChE), a group of enzymes targeted by OPs, can be used to monitor exposure to OPs; however, high variability in ChE activity may interfere with the usefulness of this technique. Several potential sources of variation in ChE activity, including water temperature, collection method, and fish sex, were investigated using bluegill collected over two consecutive summers from backwater areas of the upper Mississippi River. No ChE inhibition was found in any of the samples, nor did ChE activity vary significantly by water temperature, collection method, or sex offish. Two methods of euthanasia, spinal cord severing and anesthesia with Finquel©, were compared in bluegill collected from a small lake, to detennine potential effect on cholinesterase activity. The method of euthanasia did not affect ChE activity. Data from bluegill in the euthanasia experiment were pooled with data