Changes in sex steroid hormone levels reflect the reproductive status of captive female zebra sharks ( Stegostoma fasciatum )

Abstract Captive breedingin aquaria is a useful means for ex situ preservation of threatened elasmobranch species. To promote captive breeding, it is important to determine the female reproductivestatus. However, information regarding reproductivestatus in female elasmobranchs is limited. Here, we used zebra sharks, Stegostomafasciatum , as a model for elasmobranch reproductionin captivity. We investigated the relationships among changes in the sex steroidhormone levels, folliclesize, and egg-laying period to develop indicators for the female reproductivestatus. We confirmed that mature female zebra sharks undergo an annual reproductivecycle. Additionally, we showed that the variations in sex steroidhormone levels correlated with reproductivestatus in mature female zebra sharks. Plasma estradiol-17s (E2) concentrations increased two months before ovarian follicledevelopment and decreased along with follicleregression. Interestingly, E2 levels were inversely correlated with water temperature (R = −0.901). Moreover, high levels of testosterone (T) correlated well with the laying period. These results strongly suggest that E2 is an indicator for ovarian follicledevelopment, and that T is a useful indicator for both the onset and end of the egg-laying period in captivezebra sharks.