Environmental and endocrine regulation of seasonal reproduction in round stingrays (Urobatis halleri)

This study characterizes the seasonal reproductive cycle of round stingrays (Urobatis halleri) in Seal Beach, California. Mature round stingrays were collected monthly by beach seine near the San Gabriel River outfall from August 2004-September 2006, and rays were assessed for gametogenesis and steroid hormone levels.; Male round stingrays exhibit a clear seasonal pattern of gonadosmatic index (GSI), spermatogenesis, and production of testosterone (T) and 11-ketotestosterone (11-kT). Based on GSI, the male reproductive cycle was broken into three distinct phases. The quiescent phase (April-June) was characterized by low GSI, no spermatogenesis and suppressed androgens. The recrudescent phase (July-October) was characterized by a steady increase in GSI, the initiation of spermatogenesis to production of secondary spermatocytes, and increasing plasma levels of T and 11-kT. The degenerative phase (October-March) was characterized by a decrease in GSI, the final production of mature sperm, and further increasing androgen levels which surged in March to 132.05 ng/ml.; Female round stingrays showed no clear seasonal change in GSI ( p = 0.38). Large follicles were present throughout the entire year, while ovulation was observed in June and July both years of the study. Embryonic development continued for approximately 4 months with evidence of parturition observed in October and November. Progesterone levels were elevated in females from Seal Beach May through October.; Round stingrays exhibited strong seasonal sexual segregation in the Seal Beach National Wildlife Refuge (SBNWR). Mature female round stingrays were present in large numbers in the refuge from June to September in 2005 and 2006. Rays were found in high densities in mitigation ponds when temperatures were elevated up to 29°C, and were absent during the winter when water temperatures were reduced to 10.9°C. SBNWR females exhibited progesterone concentrations 3-fold higher than females found at Seal Beach at the same time of year. These studies suggest that female round stingrays enter warm coastal estuaries while pregnant, potentially to increase the rate of gestation; however, this requires further investigation.; This study demonstrates that steroid hormones are useful indicators of reproductive investigations of physiology and ecology in round stingrays. The reproductive physiology of round stingrays at Seal Beach, California and the SBNWR relies on both water temperature and steroid hormone concentrations.