fa Original article Original article <p dir="ltr" style="text-align: justify;"><strong>Introduction:</strong> White spot syndrome virus (WSSV) is one of the most deadly infectious pathogens of the shrimp culture industry. Neither effective vaccines nor efficient treatments are currently available for this disease. <em>Vibrio</em> species are well known dominant bacterial pathogens in the shrimp ponds. As facultative pathogenic bacteria, it is possible that <em>Vibrio</em> spp. along with WSSV to co-infect the shrimp species such as <a href="https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0ahUKEwi40Mjbg5_LAhUlS5oKHVJ4AJ0QFghPMAg&url=http%3A%2F%2Fwww.dahd.nic.in%2Fsites%2Fdefault%2Ffiles%2Ffresh_inland%2520farms%2520%25207.pdf&usg=AFQjCNGiduXLxFXNIIYyP7AxxMAEgL7rMQ&sig2=elh9qZWyPTLgXk07eO-7Ow&bvm=bv.115339255,d.bGs"><em>Litopenaeus vannamei</em></a>. The aim of this study was to investigate the co-administration of gamma-irradiated <em>Vibrio</em> <em>paraheomolyticus </em>as a kind of probiotic and immune-stimulator with gamma-irradiated and inactivated WSSV as an intramuscular vaccine for protection of <em><a href="https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=9&ved=0ahUKEwi40Mjbg5_LAhUlS5oKHVJ4AJ0QFghPMAg&url=http%3A%2F%2Fwww.dahd.nic.in%2Fsites%2Fdefault%2Ffiles%2Ffresh_inland%2520farms%2520%25207.pdf&usg=AFQjCNGiduXLxFXNIIYyP7AxxMAEgL7rMQ&sig2=elh9qZWyPTLgXk07eO-7Ow&bvm=bv.115339255,d.bGs">L. vannamei</a> </em>against WSSV infection. <strong>Methods:</strong> WSSV was isolated from the infected shrimp samples and multiplied in <em>Astacus leptodactylus </em>crayfish. Titration of WSSV was obtained in post-larvae as 10^5.4LD₅₀/ml. The virus was irradiated where D₁₀ value and optimum dose of gamma ray were calculated to be 2.56 and 15 kGy, respectively. The gamma-irradiated WSSV samples, named GI-WSSV were used as a vaccine to immunize <em>L. vannamei</em> shrimps. The freeze-dried <em>V. paraheomolyticus</em> cultures, inactivated by gamma ray (8 kGy) were named GI-V.P and used as a probiotic. <strong>R</strong><strong>esults: </strong>Protective dose50 was calculated as 5.61 and 7.94 for the shrimp groups which were vaccinated by GI&ndash;WSSV vaccine and GI-WSSV vaccine + GI-V.P, respectively. Calculated RPS values were 73.3%, 86.66% and 26.66% for the GI-WSSV vaccine, GI-WSSV + GI-V.P and isolated probiotic groups, respectively. Significant differences in cumulative mortalities were observed between the vaccination groups and the positive control group &nbsp;&nbsp;&nbsp;(P < 0.05). No significant difference was observed in cumulative mortalities between the two vaccination groups &nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;(P > 0.05). <strong>Conclusion: </strong>GI-WSSV vaccine can induce immune responses in shrimps infected with WSSV and probiotic GI-V.P enhances these responses.</p> White Spot Syndrome Virus (WSSV), Shrimp, Gamma Irradiation, Vibrio paraheomolyticus, Probiotic. 15 20 http://vacres.pasteur.ac.ir/browse.php?a_code=A-10-1-22&slc_lang=fa&sid=1 F Motamedi-Sedeh fmotamedi@nrcam.org Yes Nuclear Science and Technology Research Institute, Tehran, Iran. M Afsharnasab No Iranian Fisheries Science Research Institute, Tehran, Iran. M Heidarieh No Nuclear Science and Technology Research Institute, Tehran, Iran.