The aquaculture of the sea cucumber Apostichopus japonicus (Echinodermata, Holothuroidea) has been growing rapidly over recent years in China in response to increasing consumer demand.Indeed,it has become an important sector of the marine industry in Northern China.However,with rapid growth and the use of non-standard practices and culture techniques,epidemic diseases of A. japonicus now pose increasing problems to the industry.Therefore,the healthy aquaculture of A. japonicus is important.For a reasonable evaluation of selenium effect on sea cucumber aquaculture,using laboratory tests to simulate the sodium selenite treatment and virus infection conditions,the detection and observation of the sea cucumber body cavity fluid immune enzyme changes,pathological changes and the relative rate of protection were made.The results showed that:the change of immune enzymes in coelomic fluid of sea cucumbers under simulated sodium selenite treatments and bacteria infected conditions was tested in order to reasonably evaluate the influence of selenium on aquaculture diseases.Results indicated that the activities of superoxide dismutase(SOD),glutathione peroxidase(GPx),lysozyme(LYZ),phenoloxidase(PO)and alkaline phosphatase(ALP)in coelomic fluid rose after sodium selenite treatments were enhanced.However,SOD,GP-X and LYZ activities first ascended and then declined,and PO and ALP activities showed continued rise under additional pathogen injection into sea cucumbers,but the increasing extent of ALP activity was reduced along with increased sodium selenite concentration,and total diseased incidence rose and relative percent survival decreased under the severe sodium selenite treatment.This suggested that applying sodium selenite with moderate concentration could enhance immunity of sea cucumber to bacterial infection,but infecting also aggravated immune damage of sea cucumber by sodium selenite stress.Therefore,the diseases of cultured sea cucumber can be alleviated by optimized use of selenium.