Studies on the obstracting mechanism of Protozoa in Mass Culture of Food Organisms and its Control

1. 海洋轮虫轮状臂轮虫群体养殖的原生动物区系演替：纤毛虫（Ciliates）、长尾虫（Euplotes vannus）和乌氏线虫（Uronema sp.）在正常饲料水平的1/2 ~ 2/1范围内占优势。原生动物在食物网中的作用：分离并人工培养了大型纤毛虫E.vannus作为与海洋轮虫竞争的代表性原生动物。接种到轮虫培养物中，繁殖超过1000个/ml会阻碍轮虫的生长。利用^<15>N示踪剂进行实验，推测轮虫培养中纤毛虫占优势的机理如下：(1)在轮虫培养后期，由于轮虫过度取食而产生的死藻和附菌藻可以被纤毛虫喂养，但不能利用活藻。(2)在原木期，轮虫粪便是纤毛虫极好的食物，产量充足。然而，轮虫的贪食却与之竞争。(3)在固定阶段，轮虫的活动减少，因为有机物积累过多，细菌繁殖旺盛，纤毛虫“乐在其中”。建立了轮虫池中出现的杀轮虫的群体培养技术。对轮虫24h的ld_ <50>仅为10^4 ~ 10^5个细胞/ml。经TEM等检测，鉴定为海洋Oxnerella。这是对海洋轮虫致命的原生动物的首次记录。Sephadex柱提取的MeOH提取物的特定组分具有较强的致死率。采用高效液相色谱法测定了轮虫养殖水体中4种抗生素的残留量。两年实验的结果发表了。

1. Succession of protozoal fauna in mass culture of the marine rotifer Brachionus rotundiformis : Ciliates, Euplotes vannus and Uronema sp. were dominant in food rations from 1/2 to 2/1 of normal level.2. Function of Protozoa in food web :The larger ciliates E.vannus was isolated and artificially cultured as the representative protozoon which competes with the marine rotifer. The propagation exceeding 1000 cells/ml obstracted the growth of the rotifer when inoculated into rotifer cultures. The mechamism that the ciliate dominates in rotifer culture was postulated from experiments using ^<15>N tracer as follows.(1) In lag phase of rotifer culture, the ciliate can fed those dead and bacteria-attached algae which exist as the result of excessive feeding for the rotifer, though the ciliates can not utilize live algea. (2) In log phase, rotifer faeces, which are excellent food for the ciliate, produced enough. Scatrophagy of the rotifer, however, competes it. (3) In stationary phase, rotifer activity comes to decrease because of too much accumulation of organic substances, which makes bacteria production vigorously and the ciliate "enjoy" it.3. Killing protozoa isolated from a mass culture tankA mass culture technique of the killing Heliozoa which appeared in a rotifer tank was established. The 24hrs'LD_<50> was only 10^4-10^5 cells/ml to the rotifer. From inspections using TEM etc, it was identified as Oxnerella maritima. It is the first record of lethal Protozoa to marine rotifer. A specific fraction of MeOH extract by the Sephadex colum had strong lethality.4. The probability of Protozoa-control by antibioticsThe remaining of four antibiotics in rotifer culturing water was examined by HPLC.5. PublicationThe results of two years'experiment are published.