Previous studies suggested that the coelomic fluid or hemolymph from different aquatic invertebrates had different antibacterial spectrum and capacity,and bacterial disease is one of the primary factors limiting the development of Apostichopus japonicus aquaculture.To control the bacterial disease in A.japonicus with the immunological methods,understanding the antibacterial characteristics of coelomic fluid is necessary.However,the information about the antibacterial characteristics of coelomic fluid is limited in A.japonicus.Besides,the gradient dilution plate count method and turbidimetric method used for antibacterial analysis in previous studies are just suitable for the determination of bacteriolytic activities rather than the antibacterial activities consisting of bacteriolytic activities and bacteriostasic activities,while the method of bacterial growth curve determination,applicable to the determination of antibacterial activities,was not broadly employed.Therefore,in order to study the antibacterial spectrum of coelomic fluid from A.japonicus and the effects of divalent metal ions on the antibacterial activities of coelomic fluid,using the method of bacterial growth curve determination,we determined the effects of coelomocyte lysate supernatant and coelomic fluid supernatant from A.japonicus on the growth of Vibrio harveyi,Vibrio splendidus,Shewanella baltica,Pseudoalteromonas nigrifaciens,Staphyloccocus aureus,Micrococcus lysodeikticus,Streptococcus dysgadysgalactiae, Nocardiopsis sp.,respectively,and then determined the effects of Fe²⁺,Ca²⁺,Cd²⁺,Mg²⁺,Mn²⁺ and Zn²⁺ commonly found in marine environment on the antibacterial activities in A.japonicus coelomic fluid supernatant with M.lysodeikticus as tested bacteria.The results showed that the coelomocyte lysate supernatant had no obvious effects on the growth of all tested bacteria,while the coelomic fluid supernatant only showed strong inhibition on the growth of M.lysodeikticus.In addition,Mg²⁺ and Zn²⁺ increased the inhibition of coelomic fluid supernatant on the growth of M.lysodeikticus,while Fe²⁺,Ca²⁺,Cd²⁺ and Mg²⁺ showed no obvious effects on the antibacterial activities of coelomic fluid supernatant.The results above suggested that A.japonicus coelomic fluid in vitro only had limited-spectrum antibacterial activity,and the immune factors directly related to anti-bacteria were mainly distributed in coelomic fluid supernatant.Besides,these antibacterial factors in coelomic fluid supernatant developed a certain adaptability to the divalent metal ions that are commonly found in marine environment,and at certain concentrations,Mn²⁺ and Zn²⁺ might be beneficial to the promotion of A.japonicus antibacterial capacity.