Bayarri Maria Jose, Zanuy Silvia, Yilmaz Ozlem, Carrillo Manuel
Department of Fish Physiology and Biotechnology, Instituto de Acuicultura de Torre la Sal, Consejo Superior de Investigaciones Cientificas (CSIC), Castellon, Spain.
Chronobiol Int. 2009 Feb;26(2):184-99. doi: 10.1080/07420520902758311.
The European sea bass is a short-day breeder, a characteristic that is highly valued in aquaculture. A high percentage of males of this species mature precociously before reaching commercial size, resulting in economic losses for fish farmers. We investigated the effects of continuous light (LL) on the circadian variations of several reproductive hormones in males of this species in order to understand how the presumed absence of the melatonin rhythm caused by LL affects their daily profile. The study was conducted during four critical stages of the sea bass reproductive cycle: pre-spermatogenesis (PSpg), spermatogenesis (Spg), spermiation (Spm), and post-spermiation (PSpm). Every 3 h during a complete 24 h cycle, six fish kept under a natural photoperiod (NP), and another six fish kept under LL were anaesthetized, measured, weighed, and bled. The pituitary was removed and frozen at -80 degrees C. The pituitary content of sea bream gonadotrophin-releasing (sbGnRH) and luteinizing hormone (LH), as well as plasma content of LH, testosterone, and 11-ketotestosterone (11-KT) were analyzed by ELISA. The percentage of spermiating males (precocity) per group was determined by periodic abdominal massages of the animals. Our results confirm that LL treatment, maintained from the early stages of development onward, effectively reduces the percentage of precocious male sea bass. As has already been described for caged sea bass, plasma LH showed a clearly marked nocturnal rise near midnight during Spg and Spm during NP, but which was absent under LL. Pituitary sbGnRH and LH content and plasma LH concentration, under both NP and LL, increased during the second half of the reproductive cycle, while sexual steroids were higher at the beginning of the cycle. LL inhibited steroid secretion, especially testosterone secretion, during Spg. In summary, without photoperiod cue, as accomplished by continuous exposure to LL, circadian variations of reproductive hormones appeared altered, causing irregularities in the reproductive process of male sea bass. These findings may have a practical application in aquaculture, namely by applying LL treatment in an effort to reduce the presence of precocious males in a stock.
欧洲海鲈是短日照繁殖鱼类，这一特性在水产养殖中备受重视。该物种中很大比例的雄性在达到商业规格之前就早熟，给养鱼户造成经济损失。我们研究了持续光照（LL）对该物种雄性几种生殖激素昼夜变化的影响，以了解LL导致的褪黑素节律缺失如何影响它们的每日激素水平。该研究在海鲈生殖周期的四个关键阶段进行：精子发生前期（PSpg）、精子发生期（Spg）、排精期（Spm）和排精后期（PSpm）。在一个完整的24小时周期内，每隔3小时，对6条处于自然光照周期（NP）下的鱼和另外6条处于LL下的鱼进行麻醉、测量、称重和采血。取出垂体并在-80摄氏度下冷冻。通过酶联免疫吸附测定法（ELISA）分析垂体中黑鲷促性腺激素释放激素（sbGnRH）和促黄体生成素（LH）的含量，以及血浆中LH、睾酮和11-酮睾酮（11-KT）的含量。通过定期对动物进行腹部按摩来确定每组中排精雄性（早熟）的百分比。我们的结果证实，从发育早期开始维持LL处理，可有效降低早熟雄性海鲈的比例。正如已经描述的网箱养殖海鲈一样，在NP条件下的Spg和Spm期间，血浆LH在午夜前后显示出明显的夜间升高，但在LL条件下则没有。在NP和LL条件下，垂体sbGnRH和LH含量以及血浆LH浓度在生殖周期的后半期均升高，而性类固醇在周期开始时较高。LL在Spg期间抑制类固醇分泌，尤其是睾酮分泌。总之，在持续暴露于LL所实现的无光周期提示的情况下，生殖激素的昼夜变化似乎发生了改变，导致雄性海鲈生殖过程出现异常。这些发现可能在水产养殖中有实际应用，即通过应用LL处理来减少种群中早熟雄性的存在。
