Preliminary Observations on the Reproductive Physiology of Female Orangemouth Corvina in Captivity

Abstract

AbstractSeasonal changes In oocyte growth and plasma estradiol, testosterone, thyroid hormones and vitellogenin levels were monitored in three captive adult female orangemouth corvina Cynoscion xanthulus subjected to a condensed (8 mo) seasonal cycle of photoperiod and water temperature. Plasma concentrations of estradiol and testosterone began to rise when temperature increased to 28 C and photoperiod to 15 h light (midsummer conditions). This was accompanied by elevated circulating levels of vitellogenin and the appearance of vitellogenic oocytes (diameter > 100 μm). Estradiol concentrations and mean oocyte size increased concurrently during late summer conditions and were maximum during fall conditions, approximately 8 wk after the beginning of ovarian recrudescence. In contrast, plasma levels of thyroid hormones did not show any distinct seasonal changes. Gonadally recrudesced females contained several size classes of vitellogenic oocytes. Injection of these fish with a luteinizing hormone‐releasing hormone analog (LHRHa) caused maturation and spawning of the largest oocytes (mean diameter of follicles × 2500 μm). Another group of vitellogenic oocytes had been recruited into this size class by 2 wk after the end of spawning, which suggests that this species is capable of repeated spawning during the reproductive season. Injection of LHRHa resulted in increased plasma levels of gonadotropin and repeated spawning over several days. LHRHa‐induced final oocyte maturation, ovulation and spawning were preceded by increases in plasma levels of two teleostean maturation‐inducing steroids, 17α,20β, 21‐trihydroxy‐4‐pregnen‐3‐one (20β‐S) and 17α,20β‐dihydroxy‐4‐pregnen‐3‐one (17α,20β‐P4). The results provide preliminary evidence that oocyte growth is stimulated in orangemouth corvina subjected to an abbreviated seasonal cycle in captivity under midsummer photoperiod and temperature conditions and is associated with seasonal increases in plasma estradiol concentrations and vitellogenin production. However, the relative importance of 20β‐S versus 17α, 20β‐P4 in the control of final oocyte maturation in this species could not be determined from the results of the present study.