Investigating Annual Reproductive Hormone Patterns in Female and Male Cownose Rays
Regular transcutaneous ultrasonography of female cownose stingrays (Rhinoptera bonasus) can accurately define the reproductive status using a previously described 5-stage system. Coupling ultrasonography with plasma hormone concentrations offers the ability to further define the animal's cycle and potentially predict parturition. The latter might help reduce pup mortality. The aim of this study was to correlate the ultrasonographic reproductive staging of individual rays with reproductive hormones concentrations. Blood was drawn monthly for 10 months from 20 captive female and five captive male rays and analyzed for testosterone, androstenedione, estradiol, and progesterone. Each assay was validated for use in this species. The initial 6 months of data demonstrates a directly proportional increase in estradiol with the stage of gestation. There is an increase in both progesterone and testosterone through stage 2 of gestation, followed by a decrease to baseline for the remainder of the pregnancy. No androstenedione patterns were noted in females. Males showed a significant increase in testosterone during the months of May and June, compared to the remainder of the year. The lowest concentration of estradiol in males occurred in June. Reproductive steroid analyses appear to complement ultrasonographic findings and decreases in estradiol in full-term gestation may predict parturition.