石磺繁殖生物学的实验研究

Experimental study on the reproductive biology of Onchidium sp.

用实验室小型试验、贝类育苗场生产性试验和自然群体实地观察的方法，结合养殖池塘内石磺（Onchidium sp．）繁殖习性跟踪观察，2年内研究了沪浙地区石磺的繁殖季节，繁殖方式，繁殖力，受精卵的发育孵化，水温和盐度对胚胎发育的影响，胚胎停止发育现象，幼虫发育及变态前形态变化，对石磺繁殖生物学作了比较系统的实验研究。结果显示石磺雌雄同体，雄性先熟，异体交配，体长5cm体重10g以上的个体为繁殖的主要群体，其生物学最小型为体长3．1cm和体重3．5g；交配期多在气温22℃以上的5月中下旬至9月下旬，6-8月为繁殖盛期。产卵前经过5-10h的求爱和1-5h的交配过程，交配后15d左右产出受精卵，多在大潮日至小潮日期间3～5d内的晚间产卵；繁殖期具有6个明显的产卵高峰。卵群表面积15-30cm^2，每平方厘米卵群含卵子2650±300个，每个卵群含卵子4．4-8．0万粒。水里与潮湿环境中卵群孵化率没有明显差异；26-35℃的水温下，卵群孵化时间10-14d，水温23℃以下石磺胚胎出现停止发育的现象。适合卵群孵化的海水盐度为6～20，孵化出膜2-3d后的面盘幼虫开始摄食单胞藻。自由生活面盘幼虫经23d培育后出现明显的革质膜；变态后的幼体可能存在不断蜕去革质膜的过程，面盘幼虫的变态过程和变态条件仍有待研究。

The reproductive biology of marine pulmonate Onchidium sp., such as the copulation and spawning season, reproductive mode, fecundity, hatching and development of fertilized eggs, the effects of water temperature and salinity on embryonic development, the diapanse of embryonic development, larval development and pre-metamophosis etc., were systematically investigated through either laboratory experiment, or field observation in both mollusk hatchery and culturee ponds from 2004 to 2005. The results indicated that the marine pulmonate Onchidium sp., was protandrons hemaphrodite, and copulated with one another although the animal was often a functional male before the female organs developed. The main reproductive stocks were those of over 10 g in body weight while the smallest individual was the one with 3.1 cm long and 3.5 g in body weight. The reproductive season was usually during a period from the mid May to late September with the water temperature above 22 ℃. The period from June to August was the mating fastigium. The fertilized eggs were laid out in 15 days after courtship and mating, which usually occuffed at night in 3 to 5 days during a high tide to low tide. There were often 6 obvious peaks of egg laying. Each egg mass usually contained 44 000 to 80 000 zygotes with a surface area of 15 to 30 cm^2. The hatching rate of the egg mass were insignificantly different no matter the egg mass were kept in water or in the moist air. It would take 10 to 14 days for hatching under the temperature between 26 ℃ and 35 ℃. The embryo ceased development under 23 ℃. The suitable salinities for embryonic development were between 6 ppt and 20 ppt. The veliger began to feed on microalgae 2- 3 days after hatching. The free swimming veliger developed its periostracum of the body after a 23 day pelagic period. There might exist a process for the post-metamorphic larvae to periodically shed a cuticlelike structure from the dorsal body surface. More work still needs to be done to ascertain the condition and process of metamorphosis for pelagic veliger.