Reproductive status of captive Loggerhead sea turtles based on serum levels of gonadal steroid hormones, corticosterone and thyroxin.

Serum levels of gonadal steroid hormones, corticosterone and thyroxin (T(4)), were monitored monthly in two male and one female captive Loggerhead sea turtles (Caretta caretta) over a period of 12 months in 2004 and 3 months in 2006. Ovary ultrasonography was performed in April and July 2006. The turtles were kept together in an outdoor sea pool in natural temperature and photoperiod conditions from May to November, then in separate indoor pools from December to April. Circulating hormone levels were measured by radioimmunoassay. Oestradiol levels in the female turtle surged significantly in July, as did the progesterone level in September. Total testosterone levels were different in both males, but both peaked in September. The peaks of oestradiol in the female and testosterone in the males did not coincide, both showing delay with respect to the hormone cycle described in free-ranging Loggerhead sea turtles. A seasonal pattern in T(4) levels was not observed. The three captive turtles showed very low corticosterone levels throughout the year, with a September peak coinciding with the peaks of progesterone in females and testosterone in males. The results suggested that conditions of captivity should be as close as possible to natural conditions throughout the entire year since the process of vitellogenesis in this species is protracted. Exposure to natural conditions for only a few months is insufficient to induce reproduction/oviposition.