Abstract

The objective of this study was to evaluate the physiologic and analgesic effect of five concentrations of MS-222 (Tricaine-S, Western Chemicals, Inc., Ferndale, WA, USA) on 21 healthy adult koi (Cyprinus carpio). Each fish was exposed to five concentrations of MS-222 (50 ppm, 70 ppm, 110 ppm, 150 ppm, 190 ppm) in a random order on the same anesthetic event. Following an equilibrium period for each concentration of MS-222, vital functions such as heart rate (via Doppler) and opercular rate were recorded. A response to noxious stimuli in the form of pressure applied to the tail and lip was evaluated, and 1 cc venous blood was obtained for determination of biochemical and blood gas values.

A decrease in conscious response to noxious stimulus was inversely correlated to increases of MS-222 concentration, both for the lip and the tail stimulus (p=0.01 and p=1.8e^-5 respectively). Changes in biochemical values were not associated with changes in MS-222 concentration. However, lactate concentration was directly correlated with the length of anesthesia and the number of venipuncture procedures on each fish. Operculation rate decreased with the increase in anesthetic concentration (p=0.0003, r=0.91), while heart rate was not affected. This information may assist in establishing anesthetic protocols using MS-222 in fish and may assist in evaluating the positive effect of different analgesics in conjunction with MS-222.