Abstract
Tricaine methanesulfonate (MS-222) is an immersion anesthetic commonly used and approved for use in fish.2 MS-222 is reported to be retinotoxic in fish, frogs, and humans; although there is little clinical evidence to support that claim.1,3,4 The purpose of our study was to investigate whether repeated exposure to MS-222 would alter retinal function or induce detectable histologic retinal lesions in koi fish. We hypothesized that koi fish exposed to MS-222 for 20 minutes for 13 days would not have changes in the amplitude of ERG b-waves or histologic changes to their retina.
Eighteen koi fish (Cyprinus carpio) were utilized in the study. Prior to MS-222 exposure, two fish were euthanized, and the eyes were submitted for histology to be used as controls. The remaining fish were anesthetized with MS-222 at concentrations varying from 125–200 ppm for 20 minutes each day for up to 13 consecutive days. On day 1, anesthesia and ERG were performed on both eyes of each fish (n = 16). Following ERG measurement, two more fish were euthanized and eyes submitted for histology. On days 2 through 6, anesthesia was repeated on all fish (n = 14). On day 7, anesthesia and ERG were performed on all fish (n = 14), and histology was submitted for two more fish. On days 8 through 12, anesthesia was repeated on all fish (n = 12). On day 13, anesthesia and ERG were performed on all fish (n = 12) and histology submitted on two more fish. There were 10 fish remaining at the end of the study period.
The fish measured approximately 12 inches in length and weighed approximately 350 g. Mean b-wave amplitudes for each eye on days 1, 7, and 13 were 17.6, 25.3, 16.1 microvolts (OD), and 15.9, 18.2, 15.3 microvolts (OS), respectively. Using a Kruskal-Wallis one-way ANOVA with p value of ≤ 0.05 determining significance, consecutive b-wave amplitudes from the same eye were compared, with no significant differences among days 1, 7, and 13 (OD, p = 0.40; OS, p = 0.84). No histologic changes were identified.
In conclusion, after 13 days of daily exposure to MS-222 for 20 minutes, there were no changes in either ERG b-wave amplitudes or histology. This study suggests that short-term repeated exposure of koi fish to clinically relevant doses of MS-222 should not adversely affect retinal structure or function.
Acknowledgements
The authors wish to thank Dr. Sathya Chinnadurai of University of California, Davis, School of Veterinary Medicine and Shane Christian of North Carolina State University College of Veterinary Medicine for their medical consultation and technical assistance.
References
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