The function of Protozoa and Bacteria Coexisting in the Mas Culture of the Rotifer Brachionus Plicatilis

本研究旨在了解原生动物和细菌在轮虫（Brachionus plicatilis）培养中的作用，作为对影响海洋动物苗种计划生产的大量死亡或停滞生长的研究的一部分。在整个培养过程中，轮虫的氮转化率达到了令人难以置信的53.8-70.8%。此外，在日氮平衡方面，饲喂给动物的氮（1.89 × lo ^<-8>gN/d /轮虫）远小于生长（1.42）和排泄（2.69）的总和。这些结果表明，轮虫摄入了作为食物的藻类或酵母以外的有机物质。利用颗粒计数器进行评价，发现利用轮虫排泄物而增加的细菌和原虫在形成絮凝体后都被摄入，其摄取量与藻类或酵母的摄取量几乎相等。分离到一株对轮虫生长有显著促进作用的菌株，属假单胞菌。在轮虫突然死亡时分离到的菌株Y5对轮虫具有急性毒力，24小时LD_<50>为4-5 Log CFU/ml，可能是轮虫突然大量死亡的致病菌。细菌对轮虫培养过程中能量和物质流动的影响

This study intended to know the function of both protozoa and bacteria in the culture of the rotifer Brachionus plicatilis, as a part of researches on the massmortality or stagnan growth which disturbs the planned production of marine animal seedlingsI. Function of protozoa and bacteria in food webIncredible value of 53.8-70.8% was obtained in nitrogen conversion rate of the rotifer, when calculated on the whole culture period. Moreover, for daily nitrogen balance, the nitrogen fed to the animal(1.89xlO^<-8>gN/day/rotifer)was far less than the total of growth(1.42)and excretion(2.69). Those results suggested that the rotifer ingested organic substances other than algae or yeasts provided as food. Evaluation with Particle Counter revealed that both bacteria and drotozoa increasing by the use of rotifer's excretion were ingested after forming flocs, which was nearly equal to the value for algae or yeasts.The bacterial strain which showed remarkable growth promotion for the rotifer was isolated, and it belonged to Pseudomonas.II. Function of bacteria as a growth-inhibiting factorThe strain Y5 which had been isolated on the occasion of sudden death of the rotifer had acute virulence to the rotifer, and the 24 hrs' LD_<50> was 4-5 Log CFU/ml, which may be a causative organism of the sudden massmortality.III. Function of bacteria on the energy and substance flow in rotifer culture