In conclusion, male round stingrays exhibit an obvious annual cycle
in GSI, spermatogenesis and plasma T concentrations. 11-KT showed
increases throughout testes recrudescence and final sperm maturation,
although concentrations did not differ significantly throughout the
seasonal reproductive cycle. While peaks in GSI and spermatogenesis
occur prior to the defined mating period, increases in plasma
testosterone are associated with final sperm maturation and the onset
of copulatory activity. Temperature appears to play an important role in
plasma T regulation, as levels in wild caught male round stingrays were
negatively correlated with water temperature. Plasma T concentrations
in captive male round stingrays were rapidly affected by an increase in
water temperature to summer levels. Data from the present study and
others suggest water temperature may play a critical role in regulating
steroid hormone production, even in individuals from a thermally
variable environment such as that in Seal Beach, CA. Finally, our TUNEL
results suggest that male round stingrays may use apoptosis to regulate
testicular degeneration and homeostasis following seasonal spermatogenesis.
Together, these significant findings warrant further investigations
into the mechanisms regulating seasonal reproduction in round
stingrays and other species of elasmobranchs and teleosts.