山东沿海魁蚶繁殖周期与生化成分的周年变化

Gonad development and biochemical composition in the ark shell Scapharca broughtonii from coast of Shandong Peninsula

自2010年10月至2011年9月,对山东省鳌山卫海区魁蚶的繁殖周期、生化成分的季节变化及其与环境因子的关系进行了研究。每月采集样品1次,测定采样点水温和叶绿素a含量,采用组织学方法分析性腺的季节变化,并分别测定外套膜、闭壳肌、性腺—内脏团和足组织的生化成分(糖原、脂肪和蛋白质)含量。结果表明,该海区魁蚶雌雄比例为1∶1,雌雄性腺发育同步,全年只有1个繁殖期;配子发生始于2月,分别有25.0%和53.9%的雌雄个体性腺进入形成期,随水温和叶绿素a含量的升高而发育,6月大部分个体成熟并有部分进入排放期,至8月配子集中排放(雌:58.3%;雄:69.2%)。生化分析显示,脂肪含量在性腺—内脏团中随性腺发育积累储存,产卵后显著降低;所有组织中的糖原含量在3—7月显著高于其它月份,并且性腺中的含量高于其他组织,于5月达最大值64.2%,表明糖原在魁蚶繁殖活动中具有重要作用;蛋白质含量在除闭壳肌外的其他3种组织中出现冬季和产卵盛期两个低谷,暗示蛋白质能够弥补糖原的供能不足,与繁殖活动存在密切联系。

In East-Asian countries, the ark shell Scapharca broughtonii is one of the most commercially important shellfish resources. In China, however, the wild resources of S. broughtonii have experienced a dramatic decline in abundance for the past decades due to overfishing,declining water quality,and loss of habitat. To develop management strategies and optimize the hatchery-based seed production, the reproductive cycle and seasonal variations in biochemical composition of S. broughtonii from the coast of Shandong Peninsula were investigated from October 2010 to September 2011 in relation to environmental factors. The specimens were collected monthly, with temperature and chlorophyll a concentration in seawater column recorded synchronically. Standard histological techniques were used to analyse the gonadal development, and the seasonal cycles of the biochemical composition of separate organs of mantle, adductor muscle, gonad- visceral mass and foot were examined. Histological analysis showed a unimodal gametogenesis cycle with one spawning season （June-August） during the year. The gonads of both sexes showed synchronical development, enhancing the probability of fertilization. The gametogenesis of the ark shell initiated simultaneously with temperature and chlorophyll a concentration ascending. Mean oocyte diameter increased gradually during ovarian maturation,reaching the maximum （41.80 p,m）ahead of spawning. The sex ratio of female to male was approximately 1 ： l ,indicating that there was no difference in the quantities of both sexes inhabiting this area. Although the lipid content in the gonad was relatively low compared with those of protein and carbohydrate,it displayed a seasonal pattern coincident with the gonadal development of the ark shell,showing an evidence that it is a major component of bivalve oocytes. A significant increase in the glycogen content of all tissues during the gametogenesis suggested carbohydrates play the most important role in this species. Except for the adductor muscle, two significant decreases in the protein content were observed during the spawning peak and winter, which implied protein not only supports reproduction, but also meets the energy demand after glycogen was depleted.