Abstract

Growing interest in the field of elasmobranch reproduction has been fueled by the dire conservation status of numerous species in this taxon and the desire to shift away from wild capture of elasmobranchs for zoological populations. Relatively little is known about elasmobranch reproductive physiology compared to other species.^1-5 An increased understanding of their reproduction would improve the success of captive breeding programs and may aid in in situ conservation efforts.

In this study, the reproductive status of seven adult female white-spotted bamboo sharks (Chiloscyllium plagiosum), a non-endangered, oviparous species, was monitored using ultrasound and blood analysis (plasma biochemistry [total solids, triglyceride, iron, calcium] and steroid hormones [progesterone, testosterone and estradiol]) over four months. Females were divided into two groups: those that displayed active folliculogenesis and oviposition (n = 4) and those that did not (n = 3).

The first group was monitored by ultrasound three times per week, in addition to weekly blood analysis. The latter group was monitored via weekly ultrasound examinations and blood analysis every two weeks. Steroid hormone radioimmunoassays were validated for the species and run for each sample. For statistical analyses, blood data were categorized into three groups as follows: no follicular activity (INACTIVE, n = 22), follicles present (ACTIVE-OVARY, n = 35), and eggs present within the oviduct with or without ovarian follicles (ACTIVE-OVIDUCT, n = 14). Of the parameters analyzed, concentrations of total solids, triglyceride, calcium, progesterone, and testosterone differed (p < 0.05) among groups (mixed model repeated measures ANOVA analysis). Concentration of total solids was higher (p < 0.05) for INACTIVE (7.55 ± 0.24 g/dL) and ACTIVE-OVIDUCT (7.46 ± 0.26 g/dL) than ACTIVE-OVARY (7.11 ± 0.24 g/dL). Triglyceride concentration for the reproductively active sharks, ACTIVE-OVARY (82.90 ± 8.66 mg/dL) and ACTIVE-OVIDUCT (90.55 ± 9.66 mg/dL), was higher (p < 0.05) than the reproductively quiescent sharks in the INACTIVE group (61.95 ± 8.91 mg/dL). Calcium values were higher (p < 0.05) for ACTIVE-OVIDUCT (16.04 ± 0.21 mg/dL) than ACTIVE-OVARY (15.66 ± 0.24 mg/dL), but neither group differed from INACTIVE (16.19 ± 0.35 mg/dL; p > 0.05). Progesterone concentrations were lower (p < 0.05) for INACTIVE (mean 0.08 ng/mL, 95% CI [0.06, 0.10]) than ACTIVE-OVARY (mean 0.14 ng/mL, 95% CI [0.11, 0.18]), but both groups were similar (p > 0.05) to ACTIVE-OVIDUCT (mean 0.11 ng/mL, 95% CI [0.08, 0.17)]. There was no significant difference (p > 0.05) in testosterone concentrations between INACTIVE (mean 0.50 ng/mL, 95% CI [-0.26, 1.26]) and ACTIVE-OVARY (mean 1.76 ng/mL, 95% CI [1.06, 2.46]), but both differed (p < 0.05) from ACTIVE-OVIDUCT (mean 2.98 ng/mL, 95% CI [2.10, 3.86]). Plasma estradiol levels showed no significant difference (p > 0.05) between the subgroups. Ultrasound data was collected in a standardized manner to visualize reproductive structures consistently between individuals. The average follicle size was 1.47 ± 0.38 x 1.80 ± 0.44 cm, and the estimated average interval between seven successive ovipositions was 9.14 ± 3.99 days.

Using the described diagnostic techniques, reproductive status in white-spotted bamboo sharks can be routinely monitored in captivity, and findings have implications for improving the success of captive breeding efforts in other elasmobranch species.

Acknowledgements

Thank you to the entire aquarium staff at SeaWorld San Diego, as this project would not have been possible without their tireless efforts. Many thanks go to the veterinary internship mentors at the National Marine Mammal Foundation and U.S. Navy Marine Mammal Program, specifically Drs. Jenny Meegan and Forrest Gomez, in addition to the mentors at SeaWorld San Diego, Drs. Todd Schmitt and Hendrik Nollens. Invaluable guidance and support were also provided by Drs. Justine O'Brien and Todd Robeck. Thank you to the National Marine Mammal Foundation, SeaWorld San Diego, and the SeaWorld and Busch Gardens Reproductive Research Center, for financial and technical support for this endeavor.

* Presenting author
⁺ Student presenter

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