| In a series of five studies, the effect of the virus Baculovirus penaei, commonly known as BP, on larval and postlarval Pacific white shrimp (Penaeus vannamei) was investigated. In the first study, time required for development of patent BP infections and persistence of those infections was determined. Pre-patent infections were detected in larval shrimp at 12 hours post-inoculation (p.i). Patent infections, characterized by the presence of viral polyhedra, developed in some shrimp 18-24 hours p.i., increased in prevalence to 100% 3 to 17 days p.i. and were not detectable in most shrimp after 30 days p.i. In the second study, the effects of BP on the survival and growth of postlarval shrimp were investigated. An age-dependent pattern of disease was observed in which shrimp initially infected as larvae and young postlarvae experienced higher mortality and reduced growth, compared to older postlarvae and juveniles exposed to the virus. Immediately after a patent infection was established, postlarvae experienced high mortality in response to nutritional stress. In the third study, the biochemical response to starvation in postlarval shrimp was determined to provide a basis of comparison for nutritional and BP-induced stress. Biochemical indices, especially dry weight, RNA:DNA, protein:DNA, spermidine:DNA, spermine:DNA, and two unidentified amines expressed as a ratio to spermine, appear to be useful indicators of severe nutritional stress. In the fourth study, the relationship between BP and energy reserves in larval and postlarval shrimp was investigated. In some cases, patent BP infections were associated with a significant post-infection reduction of triacylglycerol (TAG). Experimental reduction of TAG content immediately prior to viral inoculation delayed the development of a patent infection. High pre-inoculation TAG levels were associated with increased susceptibility to BP infections. In the fifth study, the effect of BP on biochemical indices of growth was investigated. The biochemical response to BP was different from the response to nutritional stress observed earlier. The rapid and significant increases in putrescine levels of inoculated shrimp observed in this study are useful indicators of BP-induced subacute stress. |
