Developmental stages of kuruma shrimp, Penaeus japonicus Bate, susceptible to baculoviral mid‐gut gland necrosis (BMN) virus

The stages of kuruma shrimp susceptible to BMNV were determined by water‐borne infection at the fertilized egg, nauplius, zoea, mysis, and 2‐day (P‐2), 4‐day (P‐4), 6‐day (P‐6), 8‐day (P‐8) and 10‐day‐old (P‐10) post‐larval stages. Susceptibility to infection tended to decrease with advancing stages of development from zoea to P‐10. The stages from zoea to P‐4 were very susceptible, with much higher mortality and lower growth rates in virus inoculated animals compared to controls. P‐6 shrimp were also highly susceptible with all inoculated animals becoming infected with the virus. However, this group grew only slightly less well than controls and no mortality was observed. P‐8 and P‐10 post‐larvae were refractory to the disease showing no mortality and no loss of growth, even though some were slightly infected with the virus. Fertilized eggs and nauplii did not become infected with the virus using water‐borne inoculation.