Abstract

Elasmobranch stress responses have been recent topics of interest, with research focusing primarily on severe acute stress events, such as wild capture, and quantifiable assessment of acute stress using portable i-STAT blood gas analyzers.^3,6,9 Many shark species are housed in aquarium facilities and likely experience variable degrees of acute stress during common routine procedures. Increasingly, elasmobranchs are featured in touch-based exhibits, yet little work has been done to assess the effects of frequent human interactions, which could constitute a chronic stressor, on these animals. To date, chronic stress in elasmobranchs has been mainly evaluated by measuring tertiary stress responses: decreased growth rates, lower reproductive success and compromised immune function.¹⁰ Six apparently healthy adult white spotted bamboo sharks (Chiloscyllium plasiosum) housed at Mystic Aquarium were transferred from a 66cm deep exhibit tank to a 25 cm deep touch-based exhibit tank with similar water quality. The touch tank is shallow enough to allow the public to touch the sharks during operating hours and features a designated rest area where touching is not permitted. This transfer provided the opportunity to investigate 1) the degree of acute stress involved in a tank transfer procedure and 2) chronic stress induced by a touch-based exhibit, as measured by i-STAT, hematology, and plasma chemistry parameters which are commonly utilized for health monitoring. Blood was collected from each shark on four sampling events: three days before the transfer (T1), during the transfer (T2) and in the touch exhibit 14 days (T3) and 28 days post-transfer (T4). Blood gases, total protein (TP), packed cell volume (PCV) and plasma chemistry panels were performed on each blood sample. Statistical analyses of results included repeated measures ANOVA and Tukey's tests. A more acidotic state was seen during T1 and T2 sampling events, with significantly lower pH and higher PCO₂ and HCO₃, attributable to a more difficult capture procedure in the deeper tank, creating a greater acute stress response. The last two sampling events showed statistically significant patterns of increasing concentrations of blood urea nitrogen (BUN), TP and globulin. The BUN values in the first two events were similar to values seen in clinically normal sharks, whereas the BUN markedly increased above that range in T3 and T4 samples. Subsequent routine sampling on these sharks showed a return to normal BUN values within six months. The TP and globulin remained within clinically normal ranges, but manifested a statistically significant increase in the samples from the touch tank. The significant patterns of increase could be an indication that these sharks experienced chronic stressors from inhabiting the touch-based exhibit. Monitoring for chronic stress could be used to determine whether sharks acclimate over time to such interactions or if they would benefit from larger rest areas or periodic rotations out of a touch exhibit. Further investigation is required to fully determine the role of BUN, TP, and globulins in evaluating chronic stress; however, these diagnostic tests show potential in monitoring impacts of chronic stress in bamboo sharks before development of organism level impacts with tertiary stress responses.¹⁰

Acknowledgements

The authors wish to thank the staff of Mystic Aquarium: Amy DelMonaco and Lisa Mazzaro for clinical laboratory support; Gayle Sirpenski, Claire Erlacher-Reid and Jennifer Flower for data collection and sampling support; Sarah Halbrend, Rebecca Bray, Megan Priede, David Lee and Donald Harrington of the Fish & Invertebrate Department for assistance with this project.

* Presenting author
+ Student presenter

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