Abstract

Shark sedation and anesthesia is complicated by many factors, both intrinsic and extrinsic to the animal. Response to a drug often varies both between and within species. Determination of what drug or drug cocktail should be used depends on the level and duration of sedation or anesthesia desired, method and feasibility of delivery of the drug and ability to safely support and monitor the animal through recovery. Immersion and injection are the typical methods of delivery of anesthetics in elasmobranchs. Immersion is often not feasible due to the volume of drug needed and the exposure of other animals. Injection may be challenging in large systems or in tanks with potentially dangerous inhabitants. The Georgia Aquarium maintains numerous large, potentially dangerous elasmobranchs in a high volume exhibit. Safely catching, restraining or transporting these animals can be very challenging without means of chemical immobilization, thus warranting further investigation of various sedatives and anesthetics. Bonnethead sharks were chosen as a model for pilot trials. An initial goal of the pilot studies was to find a sedative or anesthetic that could be delivered orally. A secondary goal was to find a safe drug or cocktail that could be delivered orally or injectably with predictable results. Trials were carried out with azaperone, haloperidol, chloral hydrate, midazolam, propofol, acepromazine and ketamine. All were dosed intravascularly via the first dorsal sinus initially to determine an efficacious dose before administering intramuscularly (IM) or orally (PO). Delivery via the dorsal sinus was chosen as opposed to the caudal vein based on accessibility in larger species. Azaperone caused moderate to marked sedation with moderately predictable recoveries when delivered intrasinusal (IS) at 10 to 12 mg/kg. Haloperidol produced moderate sedation, but with some disorientation and injection site reactions when delivered IS at 10 mg/kg. Chloral hydrate produced sedation in some animals when dosed IS at 70 to 80 mg/kg but results were not predictable and tissue reactions were noted. Midazolam produced mild sedation with intermittent excitability when delivered IS at 5 to 8 mg/kg. Propofol was only administered IS at 4 to 5 mg/kg and produced predictable periods of anesthesia with smooth recovery. No sedation occurred when acepromazine was dosed IS up to 4 mg/kg. No sedation occurred when azaperone was dosed IM or PO, but minor tissue reactions occurred at IM injection sites. No sedation occurred when haloperidol or chloral hydrate were dosed orally; neither were administered IM due to tissue reactions noted when dosed IS. No sedation occurred with midazolam dosed to 5 mg/kg IM. Acepromazine was not administered IM or PO due to lack of efficacy IS. Ketamine, known to induce anesthesia in sharks when delivered IM, was dosed up to 30 mg/kg PO in squid with no measurable response. Additional trials and further investigation are planned in the future with bonnethead sharks and other elasmobranch species.

Acknowledgements

The authors wish to thank the members of the Georgia Aquarium veterinary and husbandry staff and the Dolphin Conservation Field Station staff that built research systems, cared for the sharks, ordered and organized supplies and assisted with drug trials. Special thanks to Drs. Mike Walsh, Andy Stamper and Ilze Berzins for advice and support. Funding for these studies was provided by the Georgia Aquarium Research and Conservation Fund.