Shewanella marisflavi is thought to be responsible for the infection in juvenile sea cucumber (Apostichopus japonicas).A bacteriophage specific to S.marisflavi was isolated from the seafood wholesale market sewage and designated as vB_SmaM_PSM (PSM-1).The phage was classified as a member of the Myoviridae family by negative staining transmission electronic microscopy (TEM).The stability of phage PSM-1 was observed after treatment with different temperature gradients and pH values.The results showed that the lytic activity of phage PSM-1 was optimal at 28 ℃ with a pH of 7.0,and ceased at temperatures higher than 60 ℃.A one-step growth curve analysis of the phage revealed eclipse and latent periods of 20 and 40 min,respectively,with a burst size of 219 PFU per infected cell.The ability of phage PSM-1 to inhibit the growth of S.marisflavi AP629 was tested in vitro using the phage with three MOI (multiplicity of infection) values of 0.1,1 and 10.All treated cultures produced an inhibition of the growth of S.marisflavi AP629 compared with the untreated culture and the treatment group with a MOI of 10 showed highest inhibition effect among the three doses.In an in vivo performance experiment,the sea cucumbers (15-20 g) were randomly assigned to five groups (1 negative control,1 antibiotic treatment group and 3 phage treatment groups) in phage injection trail as well as phage immersion trail.All groups were infected with S.marisflavi strain AP629 (3.3×106 CFU/g,LD50 level) by intraperitoneal injection.After 8 days observation,the survival rates ranged from 40% to 80% in all phage treatment groups while 10% in negative control group.Besides,the optimal therapeutic time points of the two trails were also determined.The results showed that using phage prior to infection could be a good choice to protect sea cucumbers.The overall results of this experiment indicate that using phage may be a feasible biological control agent to control S.marisflavi infection in sea cucumbers.