Abstract
From September 2008 through June 2011, seven swell sharks (Cephaloscyllium ventriosum) were housed in various indoor systems at the California Science Center. Factors in their environment (e.g., depth, cohabitants, temperature, salinity, etc.) varied slightly from system to system. They ate well, maintained weight, and mated. In June 2011, these sharks, two males and five females, were moved to an outdoor system that was a 20-foot-diameter, round, 5.5-foot-deep tank with a shade structure designed to block 70% of incoming sunlight. Four weeks after being moved outdoors, two of the swell sharks presented with multiple small areas of depigmentation on the dorsum of the body. Concurrently, all seven swell sharks stopped eating. Eight weeks after being moved outdoors, dorsal erosions started to develop at sites of depigmentation in all seven sharks. Affected skin of two sharks was biopsied, aerobic bacterial cultures of the affected skin were submitted, and the sharks were brought indoors and treated with antibiotics. No growth occurred on cultures. Histopathology revealed multifocal epidermal and dermal necrosis, pigmentary incontinence, hypopigmentation, erosion and ulceration; in ulcerated regions, there was mild bacterial colonization and moderate inflammation. Following antibiotic therapy and removal of UV exposure, swell sharks started eating over the next 2–4 weeks and cutaneous lesions gradually healed over a period of 1–3 months.
After lesions resolved, the sharks were transferred to their intended permanent housing in April 2012: a 24-foot-deep, 180,000 gallon, mixed species, kelp tank, with natural sunlight exposure. As the daylight lengthened and potential UV exposure increased, the swell sharks were monitored for cutaneous lesions. In August, some swell sharks developed depigmentation, and all were moved indoors due to the concern for UV-induced cutaneous lesions. The swell sharks were moved back outside in December when daylight hours decreased. The swell sharks were managed for 3 years by seasonal movement between outdoor and indoor tanks based on the development of cutaneous lesions and the potential for UV exposure, which included both seasonal UV exposure changes and relative cover in the tank (e.g., kelp and algae). If lesions were recognized early, they healed rapidly and without treatment as soon as the animals were brought indoors. This schedule resulted in approximately 4–6 months per year off exhibit in indoor tanks. Eventually the swell sharks were transferred to a facility with more appropriate housing where sun/UV exposure issues were not a factor.
Ultraviolet radiation induces direct DNA damage, and can result in cellular necrosis in areas of exposure.4 UV-induced solar dermatitis is well documented in teleosts, but there is little published literature concerning analogous conditions in elasmobranchs.4 Histologically, teleost solar dermatitis causes epidermal necrosis and ulceration, fewer mucous cells, and changes in pigmentation; similar changes were seen in these swell sharks.1,2,3 Secondary infections can occur in ulcerated regions, and was a mild component in these elasmobranch cases.2,4 UV-induced solar dermatitis should be considered as a possible differential for elasmobranchs with onset of dorsally-oriented cutaneous lesions corresponding to UV exposure.
Acknowledgements
The authors wish to thank Cathy Minogue of Northwest ZooPath for collating materials for this project. The authors thank the staff of the California Science Center for assistance in housing and caring for the affected sharks.
* Presenting author
Literature Cited
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