Effect of host size on virulence of Taura Virus to the marine shrimp Penaeus vannamei (Crustacea: Penaeidae)

Taura Disease (Taura Syndrome), caused by Taura Virus (Taura Syndrome Virus),is the most important disease of the farmed penaeid shrimp Penaeus vannamei in the Western Hemisphere. One possible tactic to offset Taura Virus-induced mortalities is for culturists to use larger shrimp for stocking ponds. This study consisted of 4 experiments designed to test the hypothesis that P. vannamei becomes more tolerant of Taura Virus infections as it becomes larger. Experiments were done in either 100 l glass aquaria or 4000 l cylindrical fiberglass tanks. All shrimp used in experiments were Specific-Pathogen-Free Penaeus vannamei derived from the United States Marine Shrimp Farming Program Population 1. The Taura Virus in all experiments originated from infected farm-reared shrimp collected during a 1995 Taura Virus outbreak in Texas, USA. Experimental shrimp were inoculated with virus either per os by allowing shrimp to feed on triturated infected shrimp tissue or intramuscularly by injection of a cell-free suspension of infected shrimp tissue into the abdominal musculature. In the 4 experiments 9 to 14 d survival ranged from 0 to nearly 60 %. Analysis of each of the 4 experiments by logistic regression revealed a consistent trend for larger shrimp to be more likely to succumb to infection; however, the effect was only statistically significant in 2 of the 4 experiments. The results of the experiments failed to support the hypothesis that P. vannamei increases its tolerance to Taura Virus as it increases in size from 1 to 30 g.