Abstract
Koi carp are commonly anesthetized with tricaine methanesulfonate (MS-222), a local anesthetic with an unknown mechanism of action as a general anesthetic. MS-222 must be reconstituted and buffered before administration, so it would be useful to identify an alternative anesthetic for fish whose mechanism of action is known, does not require reconstitution, and is already at a physiologic pH. The purpose of this study was to determine the efficacy of propofol, a GABA agonist, as an immersion anesthetic agent in koi carp. Ten adult koi weighing between 230 to 459 gm were used in a crossover study. Koi were exposed to each of four concentrations of propofol (1, 2.5, 5, and 10 mg/L) with a 1 week washout period between trials. In a fifth trial, koi were anesthetized with 5 mg/L propofol and maintained with 3 mg/L for 20 minutes using a recirculating system. Induction and recovery times were recorded. Heart rate and opercular rate were recorded following induction in all koi and after 20 minutes of anesthesia in those kept anesthetized on the recirculation system. In the 5th trial, biochemical parameters were assessed immediately after induction and following 20 minutes of anesthesia. Response to pain was assessed by reaction to a needle insertion into muscle. Potential differences between groups were tested with a Friedman analysis. At 1 mg/L, koi were deeply sedated but never anesthetized. At propofol concentrations of 2.5, 5, and 10 mg/L, median induction time was 13.4, 3.6, and 2.3 minutes, respectively. Induction time of koi receiving the greatest dose was significantly shorter than those receiving the lowest dose (p < 0.0001). Median recovery time was not different between the doses (p = 0.40) and in groups immersed in 2.5, 5, and 10 mg/L was 10.4, 9.1, and 15.0 minutes, respectively. At 2.5, 5 and 10 mg/L, median heart rate was 64, 30 and 22, respectively. Koi receiving the lowest dose had a higher HR compared with koi receiving the highest dose (p = 0.006). Median opercular rate following induction was not different between the groups (p = 0.07) in koi immersed in 2.5, 5, and 10 mg/L was 56, 66 and 54, respectively. Responses to a needle insertion at 2.5, 5, and 10 mg/L were 1/10, 2/10 and 0/10, respectively. Following induction and after 20 minutes of anesthesia, blood pH was 7.28 and 7.35 respectively, and lactate was 3.98 and 2.58 mmol/L, respectively. One koi in the fifth trial never completely recovered from anesthesia and was subsequently euthanized. Propofol at 2.5 mg/L or greater was successful in producing anesthesia in koi.
Acknowledgements
This research was supported by the George H. Hitchings New Investigator Award in Health Research.
* Presenting author