Viable cell count was used to determine whether Metschnikowia sp.C14 can colonize the intestine of juvenile sea cu-cumber Apostichopus japonicus.Sea cucumber individuals were divided into two groups,which were fed the control diet for 38 days or the C14-supplemented diet at 105 cells g?1 diet for 28 days,then the control diet from day 29 to day 38.The number of C14 cells in the intestine of sea cucumber fed the C14-supplemented diet significantly increased from day 7 to day 28,and decreased from day 29 to day 38.Sea cucumber fed with the diet containing C14 showed a significant increase in trypsin activity and lipase activity from day 21 to day 33 compared with the control.Feeding C14 significantly improved the phagocytic activity and respiratory burst in coelomocytes from day 21 to day 35 and from day 14 to day 38,respectively.In addition,there was an obvious enhancement in ly-sozyme activity (from day 21 to day 38 or day 33),phenoloxidase activity (from day 21 to day 28) and total nitric oxide synthase activity (from day 14 to day 38) in coelomic fluid supatant and/or coelomocyte cell lysate supatant compared with the control.There were significant positive correlations between the number of C14 cells colonizing the intestine and trypsin activity of the intes-tine,lysozyme activity of the coelomic fluid supatant and coelomocyte lysate supatant from sea cucumber.These data sug-gested that the number of C14 cells should be maintained at 105 cfu (colony-forming units) g?1 intestine material for the maximum benefit.