Organophosphate and carbamate insecticides produce their toxic effects by binding with cholinesterase enzymes, resulting in the inhibition of acetylcholine catabolism.1 Excessive acetylcholine levels cause excessive synaptic neurotransmitter activity.2 In most animal species, whole blood is the preferred sample for evaluation of cholinesterase activity. Previous reports of cholinesterase activity in carp have involved sampling of serum, plasma, brain, liver, muscle, and heart.3-5
Whole blood samples were obtained from 12 healthy koi (Cyprinus carpio). Whole blood cholinesterase activity was measured in all 12 samples. Because one sample was clotted, its analysis was performed primarily on plasma. To evaluate if this may have significantly affected the result, plasma cholinesterase activity was also measured in four additional samples.
The overall average of the whole blood cholinesterases was 0.08 mcmol/ml/min (SD=0.024). With the value from the clotted sample removed, the average becomes 0.075 mcmol/ml/min (SD=0.019). The results for the plasma cholinesterases were not very different, with an average of 0.08 mcmol/ml/min (SD=0.012). Since these reference values are close to the minimum detection limit for the method of analysis used, evaluation of blood samples from koi suspected to be suffering from anticholinesterase toxicity may be difficult.
The authors would like to thank Mr. Larry Christian and Dr. Craig Harms for their assistance with this project.
1. Meerdink GL. 1989. Organophosphorus and carbamate insecticide poisoning in large animals. Veterinary Clinics of North America: Food Animal Practice 5(2):375-389.
2. Osweiler GD. 1996. Organophosphorus and carbamate insecticides. In: Toxicology. Williams & Wilkins, Philadelphia, pp.231-236.
3. Kozlovskaya VI, FL Mayer, OV Menzikova, et al. 1993. Cholinesterases of aquatic animals. Reviews of Environmental Contamination and Toxicology 132:117-142.
4. Keizer J, G D'Agostino, R Nagel, et al. 1995. Enzymological differences of AchE and diazinon hepatic metabolism: correlation of in vitro data with the selective toxicity of diazinon to fish species. The Science of the Total Environment 171:213-220.
5. Szabo A, J Nemcsok B Asztalos, et al. 1992. The effect of pesticides on carp (Cyprinus carpio L). Acetylcholinesterase and its biochemical characterization. Ecotoxicology and Environmental Safety 23:39-45.