Abstract

Bamboo sharks are some of the most common elasmobranch species in zoos and aquaria and are frequently sedated for medical exams, treatments, and research. Capture and restraint of elasmobranchs can be a stressful event that can induce fatal lactic acidosis.^1,2 Published sedation and anesthesia protocols commonly utilize immersion anesthetic drugs, such as tricaine methanesulfonate (MS-222), which may not be practical based on size or community tank constraints, or intravenous drugs, which require substantial manual restraint or prior use of an immersion or intramuscular sedative to facilitate intravenous access.^3-8 Intramuscular sedation offers a minimally invasive way to sedate elasmobranchs and can even be performed underwater with a pole syringe in community tanks.^6,9 Many intramuscular drugs may also be reversible, which can decrease recovery time and allow quicker return to a community setting following handling.⁵

The objectives of this study were 1) to assess the efficacy of novel, reversible, intramuscular sedation protocols in bamboo sharks and 2) to assess possible adverse effects associated with sedation in those sharks.

A final study protocol of dexmedetomidine (0.05 mg/kg) and midazolam (2.0 mg/kg) given intramuscularly was chosen based on eight pilot studies investigating different doses and drug combinations. I-STAT blood values were measured for study (n=8) and control (n=2) sharks before sedation and at the time of reversal with atipamezole (0.5 mg/kg IM) and flumazenil (0.05 mg/kg IM), 60 minutes after sedation. Sedated sharks were serially assessed every five minutes for voluntary movement, branchial beats, righting reflex, heart rate, response to external coelom stimulation, response to cloacal stimulation, pelvic fin reflex, response to noxious stimulus, and ability to swim.

All sedated sharks achieved a handleable plane of sedation that would allow for minimally invasive procedures, with significantly decreased response to noxious stimulus, voluntary movement, righting reflex, coelomic response, cloacal response, and ability to swim, which rapidly returned to normal after administration of reversal agents. Branchial beats, but not heart rate, significantly decreased in sedated sharks, to a minimum of 32 branchial beats per minute in one shark. Sedated sharks had a significant increase in lactic acid (4.20 mmol/L vs. <0.37 mmol/L, p=0.0004) and a decrease in blood pH (7.46 vs. 7.28, p=0.0012) compared to pre-sedation levels, but neither required clinical intervention based on predetermined intervention cutoffs.¹⁰ Sharks rapidly regained function after the administration of reversal agents and were clinically normal 30 minutes after reversal. This study demonstrates a novel intramuscular sedation protocol that was effective at inducing a workable plane of sedation for minimally invasive procedures and was rapidly reversible. The protocol did not induce lactic acidosis that necessitated clinical intervention, and sharks were sedated, recovered, and returned to their community tanks without incident.

Acknowledgments

The authors gratefully acknowledge Brittney Goodwin, Emily Smith, Jackie Simson, and Jeffery Nishimura for their help with data collection, Rachel Munson for animal husbandry, and Dr. Phillip Kass for providing statistical advice.

*Presenting author
⁺Student presenter

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