fa fish disease fish disease پژوهشي Orginal research papers <p><a name="OLE_LINK25"></a><a name="OLE_LINK3"></a><a name="OLE_LINK16"></a><a name="OLE_LINK13">In this research, White spot syndrome virus (WSSV) with 10^5.4LD₅₀.mL^-1 inactivated with gamma irradiation at a dose rate of 14-15 kGy.sec^-1 was used as a vaccine. Three hundred and sixty shrimp of <em>Litopenaeus vannamei, </em>medium body weight (MBW) 1.0&plusmn;0.17g), were prepared and experimentally exposed. They were distributed among four groups, inclusing vaccinated-virus exposed (T1), vaccinated-nonvirus exposed (T2), virus exposed (Positive control as T3) and non-vaccinated-non-virus exposed (Negative control as T4). The mortality percent of T1 started from day 5 and reached the highest (50%) on day 11 and remained constant until end of the experiment. In T2, no mortality was observed until the 3^rdday and the maximum mortality (20%) was observed on day 9. On the other hand, no remarkable mortality was recorded for T4 unlike T3 in which the mortality started on day 2 and stopped on day 7. The minimum density of hyalinocyte was calculated in T4 but the maximum one was found in T3 (17.77&plusmn;0.33) with no significant differences (<em>p</em><0.05) compared to T2 (16.59&plusmn;0.96). A significant difference (<em>p</em><0.05) was observed between the values of Total Haemocyte Count (THC) before and after exposing to virus in T1. Total Protein Plasma (TPP) decreased to 29.03&plusmn;3.41, while it was higher than 25.96&plusmn;2.75 in T3 after 7 days. Such results might be responsible for developing resistance against WSSV in gamma irradiant vaccine in <em>L. vannamei</em> in comparison to T3 while the cause of mortality in T2 could be due to the lower effectiveness.</a></p> WSSV, Gamma irradiant, Haemolymph parameters, Mortality rate 382 396 http://jifro.ir/browse.php?a_code=A-10-23-10&slc_lang=fa&sid=1 D. Boreyri damonboreyri@yahoo.com 100319475328460038083 100319475328460038083 No M. Afsharnasab 100319475328460038084 100319475328460038084 Yes A.A. Motalebi 100319475328460038085 100319475328460038085 No A. Haghigh 100319475328460038086 100319475328460038086 No