Factors affecting brain cholinesterase activity in bluegill (Lepomis macrochirus)

Organophosphorus insecticides (OPs) are widely used to control crop pests, and can enter aquatic systems draining agriculturalwatersheds. Because OPs are highly toxic to aquatic organisms,monitoring is important, yet difficult due to the low persistenceof many OPs. Cholinesterase (ChE) inhibition can be used to monitor organisms' exposure to OPs and carbamates; however, highvariability in ChE activity may interfere with the ability of theassay to detect OP exposure. Several potential sources of variation in ChE activity, including water temperature, storage of samples, euthanasia method, and fish sex and size, were investigated in bluegill (Lepomis macrochirus). ChE activity did not vary significantly with water temperature in the range 20–31 °C, or following short-term storage ofeuthanized bluegill up to 8 h at 4 and 19 °C or long-term storage of brain homogenates up to 389 d at –198 °C. There was no difference in ChE activity by euthanasia method (spinal cord severing or anesthesia with Finquel®), nor by sex of fish. Mean ChE activity variedinversely with fish total length. Of the variables investigated in this study, only size needs to be restricted in fish collectedfor monitoring of OPs.