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Effect of manipulation of dietary rotifer Brachionus plicatilis bacterial flora on the intestinal bacterial flora of Japanese flounder Paralichthys olivaceus larvae was investigated. Manipulation was done by disinfecting rotifer eggs to reduce viable bacterial counts and then by inoculating hatched rotifers with non-sucrose fermenting Vibrio splendidus strain V-15 to make the bacterium dominant in the rotifers. Flounder larvae were fed the manipulated rotifers and intestinal bacterial flora of the fish was monitored. The dominant intestinal bacterial flora of the flounder became Vibrio spp. These results indicate that intestinal bacterial flora of flounder can be artificially controlled by manipulating bacterial flora in diets., 消毒前のワムシ卵および未処理区の孵化ワムシの細菌叢は，共にFlavobacterium属が主体を成していたことから，孵化前後でワムシの菌叢は変化しないことが示された。また，消毒して孵化させた後にV. splendidus V-15株を添加した区のワムシの細菌叢はVibrio属が主体を成していた。これらの結果から，ワムシの細菌叢は制御可能であることが示唆された。次いで，ショ糖分解能のない抗ウイルス活性を有するV. splendidus V-15株優勢ワムシをヒラメに給餌した。ヒラメ腸管内におけるVibrio属細菌のうち，ショ梼非分解薗の割合は未処理区で62%，消毒区で59%，菌添加区で100%となり，ヒラメの腸内細菌叢も制御可能であることが示唆された。

Treatment of supplied water with a high quality ultraviolet (UV) lamp was examined for prevention of scuticociliatosis of farmed juvenile Japanese flounder (Paralichthys olivaceus). In an examination for the ciliate-cidal effect of UV irradiation, scuticociliates showed low susceptibility to UV compared with fish pathogenic viruses or bacteria, the minimal killing dosage being 2.0 × 10^5 μW・sec/cm^2. UV treatment of supplied water to the tank was performed in a flounder farm in southern Hokkaido, where scuticociliatosis frequently occurred. It was revealed that the UV treatment at 3.0 × 10^5 μW・sec/cm^2 was effective to prevent scuticociliatosis.