Whole-blood and plasma cholinesterase levels in normal koi (Cyprinus carpio)

Organophosphate and carbamate insecticides produce their toxic effects by binding with cholinesterase enzymes, resulting in the inhibition of acetylcholine catabolism. Excessive acetylcholine levels cause excessive synaptic neurotransmitter activity. 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. Whole-blood samples were obtained from 12 healthy koi (Cyprinus carpio). Whole-blood cholinesterase activity was measured in all 12 samples. Plasma cholinesterase activity was also measured in 4 samples. The overall average of the whole-blood cholinesterases was 0.08 micromol/ml/minute (SD = 0.024). The results for the plasma cholinesterases were similar, with an average of 0.08 micromol/ml/minute (SD = 0.012). Because these reference values are below the minimum detection limit for the method of analysis used, results from blood samples from koi suspected to be suffering from anticholinesterase toxicosis may be uninterpretable.