Abstract

Anesthetic agents such as tricaine methanesulfonate (MS-222) may facilitate medical procedures and limit potential stress and pain associated with handling in fish and other aquatic species.^1,3 Though jellyfish are commonly maintained in public aquaria and for research, there are very few reports describing anesthetic protocols in this taxa.³ A previous study in a single population of moon jellyfish (Aurelia aurita) showed that 0.3 and 0.6 g/L of MS-222 reduced movement and response to stimuli.² However, there is still limited data on the optimal dose of MS-222 in this and other species of jellyfish.^2,3 The objective of this study was to investigate the effects of MS-222 on movement and response to stimuli in moon jellyfish and flame jellyfish (Rhopilema esculentum).

Moon and flame jellyfish under human care from the Vancouver Aquarium were selected for this prospective, randomized, unblinded, controlled clinical trial. Twelve individuals of each species were separated into two groups of six: control moon jellyfish (AACON), treatment moon jellyfish (AAMS-222), control flame jellyfish (RECON), and treatment flame jellyfish (REMS-222). Based on a pilot study with two additional flame jellyfish, a concentration of 0.3 g/L MS-222 was chosen for the treatment group. Control groups were tested in sea water with no additional additives. A scoring system to observe response to stimuli, body tone, and bell contraction quality was adapted from a previous study and a cutoff defined.² Water temperature and pH were measured, and baseline scores were recorded. Jellyfish were placed in their assigned solution and scored every minute until they reached the cutoff or a maximum of 15 minutes. Bell diameter and response to an injection of saline was recorded. AAMS-222 and REMS-222 were placed in drug-free water and time to recovery (return to baseline scores) was recorded. Due to small sample size, the Wilcoxon rank-sum test was used to compare groups.

Temperature for AAMS-222 (10.8°C) was lower than REMS-222 (24.1°C, p=0.005). pH for AAMS-222 (7.26) was lower than AACON (7.82, p=0.005) and RE-MS-222 (7.30) was lower than RECON (7.89, p=0.005) but was similar between both MS-222 groups (p=0.46). The median time to cutoff was 1.11 minutes for AAMS-222 (6/6) and 9.26 minutes for REMS-222 (4/6). AAMS-222 reached the cutoff faster than RE MS-222 (p=0.01). Time to recovery was similar for all six individuals in both AAMS-222 (5.28 minutes) and REMS-222 (4.65 minutes, p=1.00). Bell diameter for AAMS-222 (8.2 cm) was similar to REMS-222 (6.9 cm, p=0.15). No response to injection was observed in any group, and 6/6 AACON, 6/6 RECON, 0/6 AAMS-222, and 3/6 REMS-222 maintained spontaneous movement. All jellyfish were recovered, and there were no mortalities for one week post trials.

MS-222 at 0.3 g/L reduces spontaneous movement and response to stimuli in moon and flame jellyfish, with more pronounced effects in moon jellyfish. Further research is needed to investigate the effects of species, dose, temperature, pH, and individual variability on drug responses in jellyfish.

Acknowledgements

The authors wish to thank Eric Lee for help with data collection, Braeden Schiltroth, Jenna Macleod, and Danny Kent for animal care and management, and Sion Cahoon, Gabrielle Beer, Natalie Sacks, Alyssa Blew, and the Vancouver Aquarium for providing support throughout the project.

*Presenting author
+Student presenter

Literature Cited

1.  Cooper JE. Anesthesia, analgesia, and euthanasia of invertebrates. ILAR J. 2011;52(2):196–204.

2.  Gorges MA, Martinez KM, Labriola NF, Phillips BE, Christian LS, Chen EP, Posner LP, Lewbart GA, Dombrowski DS. Effects of tricaine methanesulfonate in a managed collection of moon jellyfish (Aurelia aurita). J Zoo Wildl Med. 2022;53(1):100–107.

3.  Stoskopf MK, Freeman KS. Jellyfishes (Ctenophora and Scyphozoa). In: Lewbart GA, ed. Invertebrate Medicine. 3rd ed. Hoboken, NJ: Wiley Blackwell; 2021:33–49.