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

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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