Serum concentrations of steroid hormones during reproduction in the Atlantic stingray, Dasyatis sabina

The Atlantic stingray, Dasyatis sabina, has a well-defined annual reproductive cycle in Florida. We collected adult specimens over 12 months and evaluated reproductive parameters and serum levels of five steroid hormones, 17 beta-estradiol (E-2), progesterone (P-4), testosterone (T), dihydrotestosterone (DHT), and corticosterone (CS). Female E-2 peaked twice, once in mid-March to early April in association with ovulation and again in mid-June to mid-July in association with the enlargement of a second group of ovarian follicles. Female P-4 peaked in early March and early April, coincident with the peak in E-2. Female DHT was variable but exhibited a pattern not clearly associated with known events in the reproductive cycle. Female T and CS levels did not vary significantly through time. In males, T DHT, anti CS increased progressively through winter and spring, peaking in March when females were ovulating and when copulation probably took place. DHT concentrations were usually at least twice T levels. These three hormones peaked long after the November/December peak in gonadosomatic index. E-2 was measurable in males and was highest during the period of testicular development. Male P-4 varied in a pattern not clearly associated with known reproductive events.