Reproductive Parameters and Changes in Blood Levels of Steroid Hormones and Minerals in the Hawksbill Turtle Eretmochelys imbricata in an Aquarium

The hawksbill turtle Eretmochelys imbricata is listed as “critically endangered” on the Red List of International Union for Conservation of Nature; it requires in situ and ex situ conservation. To establish an effective captive breeding technique for the hawksbill turtles, its reproductive parameters and behavior in captivity, and the physiological changes, including hormonal changes, that lead to egg laying must be understood. Here, we observed the mating behavior of male (n=5) and female (n=3) hawksbill turtles (housed in a tank) from 2003 to 2007. We regulated the tank water temperature and daylight hours to simulate their natural environment. We sampled their blood at regular intervals to measure plasma concentrations of minerals and sex hormones. One (No. Ei21) of the female turtles was reproductively more active than others. Further, males mounted it more frequently than others. Subsequently, the female (Ei21) laid eggs twice, on 10 May and 8 July 2003. Females including Ei21 showed annual changes in 17β-estradiol and progesterone (P4) levels, whereas males showed annual changes in testosterone levels. Plasma calcium (Ca) level peaked in only the egg laying turtle (Ei21); however, inorganic phosphorus did not show a sharp increase. In 2005, as in 2003, Ei21 underwent similar physiological changes. We conclude that this phenomenon—of rapid rise in plasma P4, a hormone elevated after ovulation, followed immediately by a rise in plasma Ca level—is likely involved in the eggshell formation after ovulation. In future, we will further investigate these phenomena in hawksbill turtles.