2-Phenoxyethanol (2-PE) and Tricaine Methanesulfonate (MS-222) Immersion Anesthesia of American Horseshoe Crabs (Limulus polyphemus)
Abstract
Despite extensive literature examining American horseshoe crab physiology, there are comparatively few publications addressing their medical care.1-9 Establishing anesthesia protocols for horseshoe crabs is integral to limiting the potential stress and pain associated with invasive procedures, and for advancing euthanasia techniques. The objective of this study was to compare the effects of two immersion anesthetics, tricaine methanesulfonate (MS-222) at 1 g/L (buffered with sodium carbonate) and 2-phenoxyethanol (2-PE) at 2 mL/L, on horseshoe crabs. Twenty horseshoe crabs were assigned to one of two anesthetic treatment groups and individually anesthetized in natural sea water. Water quality, cardiac contractility, and hemolymph gas analyses were measured prior to anesthesia and at 30 minutes. Animals were monitored via heart rate, gilling rate, and sedation score every 5 minutes until recovered. Trans-carapacial ultrasonography was used to obtain heart rate, gilling rate, and percent fractional shortening. Light or surgical anesthesia was produced in 10/10 animals in the 2-PE group and 8/10 animals in the MS-222 group. There was no significant difference in sedation scores, induction (median 15 minutes) or recovery time (median 20.5 minutes). Gilling rate and cardiac contractility decreased during anesthesia, whereas heart rate did not. Hemolymph pH and pO2 were not different among treatment groups or time points. Invasive blood pressure obtained via cardiac catheterization in two animals was markedly decreased during surgical anesthesia. In conclusion, 2-PE and MS-222 provided effective anesthesia with clinically useful induction and recovery times. 2-PE provided a subjectively more reliable and smoother anesthesia compared to MS-222.
Acknowledgements
The authors thank Josh Summers for his assistance obtaining animals for this study, and Chloe Mickles, Claire Pelletier, Heather Broadhurst, and Sheldon Perry for their invaluable technical support.
* Presenting author
+ Student presenter
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