Photoperiod and water temperature regulation of seasonal reproduction in male round stingrays ( Urobatis halleri)

Abstract

This study characterizes the seasonal reproductive cycle of male 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 seasonal pattern of increased gonadosomatic 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. TUNEL positive staining was only observed in the Sertoli cells of mature spermatocysts during the degenerative testicular phase, suggesting that Sertoli cell death potentially plays a role in testicular degeneration and the regulation of sperm release. GSI, T, and 11-KT were all inversely correlated with daylength, while only T was inversely correlated with temperature. Captive male round stingrays subjected to water temperatures of 25 °C showed a significant decrease in plasma testosterone concentrations, but the same males exposed to ambient water temperatures (18 °–20 °C) exhibited T concentrations observed in wild male round stingrays during the recrudescent phase. Together, these findings suggest that temperature plays an important role in the regulation of testosterone, and may serve as an ultimate cue for reproduction in male round stingrays.